* [PATCH v11 02/14] arm64: barrier: Support smp_cond_load_relaxed_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
Support waiting in smp_cond_load_relaxed_timeout() via
__cmpwait_relaxed(). To ensure that we wake from waiting in
WFE periodically and don't block forever if there are no stores
to ptr, this path is only used when the event-stream is enabled.
Note that when using __cmpwait_relaxed() we ignore the timeout
value, allowing an overshoot by up to the event-stream period.
And, in the unlikely event that the event-stream is unavailable,
fallback to spin-waiting.
Also set SMP_TIMEOUT_POLL_COUNT to 1 so we do the time-check in
each iteration of smp_cond_load_relaxed_timeout().
And finally define ARCH_HAS_CPU_RELAX to indicate that we have
an optimized implementation of cpu_poll_relax().
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Suggested-by: Will Deacon <will@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
arch/arm64/Kconfig | 3 +++
arch/arm64/include/asm/barrier.h | 21 +++++++++++++++++++++
2 files changed, 24 insertions(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9ea19b74b6c3..e3ce08276e9b 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1628,6 +1628,9 @@ config ARCH_SUPPORTS_CRASH_DUMP
config ARCH_DEFAULT_CRASH_DUMP
def_bool y
+config ARCH_HAS_CPU_RELAX
+ def_bool y
+
config ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
def_bool CRASH_RESERVE
diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 9495c4441a46..6190e178db51 100644
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -12,6 +12,7 @@
#include <linux/kasan-checks.h>
#include <asm/alternative-macros.h>
+#include <asm/vdso/processor.h>
#define __nops(n) ".rept " #n "\nnop\n.endr\n"
#define nops(n) asm volatile(__nops(n))
@@ -219,6 +220,26 @@ do { \
(typeof(*ptr))VAL; \
})
+/* Re-declared here to avoid include dependency. */
+extern bool arch_timer_evtstrm_available(void);
+
+/*
+ * In the common case, cpu_poll_relax() sits waiting in __cmpwait_relaxed()
+ * for the ptr value to change.
+ *
+ * Since this period is reasonably long, choose SMP_TIMEOUT_POLL_COUNT
+ * to be 1, so smp_cond_load_{relaxed,acquire}_timeout() does a
+ * time-check in each iteration.
+ */
+#define SMP_TIMEOUT_POLL_COUNT 1
+
+#define cpu_poll_relax(ptr, val, timeout_ns) do { \
+ if (arch_timer_evtstrm_available()) \
+ __cmpwait_relaxed(ptr, val); \
+ else \
+ cpu_relax(); \
+} while (0)
+
#include <asm-generic/barrier.h>
#endif /* __ASSEMBLER__ */
--
2.31.1
^ permalink raw reply related
* [PATCH v11 14/14] kunit: add tests for smp_cond_load_relaxed_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
Add a success and failure case for smp_cond_load_relaxed_timeout().
Both test cases wait on some state in smp_cond_load_relaxed_timeout().
In the success case we spawn a kthread that pokes the bit.
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
lib/Kconfig.debug | 10 +++
lib/tests/Makefile | 1 +
lib/tests/barrier-timeout-test.c | 125 +++++++++++++++++++++++++++++++
3 files changed, 136 insertions(+)
create mode 100644 lib/tests/barrier-timeout-test.c
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 93f356d2b3d9..dcd2d60a9391 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2398,6 +2398,16 @@ config FPROBE_SANITY_TEST
Say N if you are unsure.
+config BARRIER_TIMEOUT_TEST
+ tristate "KUnit tests for smp_cond_load_relaxed_timeout()"
+ depends on KUNIT
+ default KUNIT_ALL_TESTS
+ help
+ Builds KUnit tests that validate wake-up and timeout handling paths
+ in smp_cond_load_relaxed_timeout().
+
+ Say N if you are unsure.
+
config BACKTRACE_SELF_TEST
tristate "Self test for the backtrace code"
depends on DEBUG_KERNEL
diff --git a/lib/tests/Makefile b/lib/tests/Makefile
index 05f74edbc62b..3504d677b7b8 100644
--- a/lib/tests/Makefile
+++ b/lib/tests/Makefile
@@ -20,6 +20,7 @@ CFLAGS_fortify_kunit.o += $(DISABLE_STRUCTLEAK_PLUGIN)
obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_kunit.o
CFLAGS_test_fprobe.o += $(CC_FLAGS_FTRACE)
obj-$(CONFIG_FPROBE_SANITY_TEST) += test_fprobe.o
+obj-$(CONFIG_BARRIER_TIMEOUT_TEST) += barrier-timeout-test.o
obj-$(CONFIG_GLOB_KUNIT_TEST) += glob_kunit.o
obj-$(CONFIG_HASHTABLE_KUNIT_TEST) += hashtable_test.o
obj-$(CONFIG_HASH_KUNIT_TEST) += test_hash.o
diff --git a/lib/tests/barrier-timeout-test.c b/lib/tests/barrier-timeout-test.c
new file mode 100644
index 000000000000..d72200daa0f2
--- /dev/null
+++ b/lib/tests/barrier-timeout-test.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests exercising smp_cond_load_relaxed_timeout().
+ *
+ * Copyright (c) 2026, Oracle Corp.
+ * Author: Ankur Arora <ankur.a.arora@oracle.com>
+ */
+
+#include <linux/bitops.h>
+#include <linux/types.h>
+#include <linux/sched/clock.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <asm/barrier.h>
+#include <kunit/test.h>
+#include <kunit/visibility.h>
+
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
+
+struct clock_state {
+ s64 start_time;
+ s64 end_time;
+};
+
+#define TIMEOUT_MSEC 2
+#define TEST_FLAG_VAL BIT(2)
+static unsigned int flag;
+
+static s64 basic_clock(struct clock_state *clk)
+{
+ clk->end_time = local_clock();
+ return clk->end_time;
+}
+
+static void update_flags(void)
+{
+ WRITE_ONCE(flag, TEST_FLAG_VAL);
+}
+
+static s64 mock_clock(struct clock_state *clk)
+{
+ s64 clk_mid = clk->start_time + (TIMEOUT_MSEC * NSEC_PER_MSEC)/2;
+
+ clk->end_time = local_clock();
+ if (clk->end_time >= clk_mid)
+ update_flags();
+ return clk->end_time;
+}
+
+typedef s64 (*clkfn_t)(struct clock_state *);
+
+static void test_smp_cond_relaxed_timeout(struct kunit *test,
+ clkfn_t clock, bool succeeds)
+{
+ struct clock_state clk = {
+ .start_time = local_clock(),
+ .end_time = local_clock(),
+ };
+ s64 runtime, timeout_ns = TIMEOUT_MSEC * NSEC_PER_MSEC;
+ unsigned int result;
+
+ result = smp_cond_load_relaxed_timeout(&flag,
+ (VAL & TEST_FLAG_VAL),
+ clock(&clk),
+ timeout_ns);
+
+ runtime = clk.end_time - clk.start_time;
+ KUNIT_EXPECT_EQ(test, (bool)(result & TEST_FLAG_VAL), succeeds);
+ KUNIT_EXPECT_EQ(test, runtime <= timeout_ns, succeeds);
+}
+
+static int smp_cond_threadfn(void *data)
+{
+ udelay(TIMEOUT_MSEC * USEC_PER_MSEC / 4);
+
+ /*
+ * Update flags after a delay to give smp_cond_relaxed_timeout()
+ * time to get started.
+ */
+ update_flags();
+ return 0;
+}
+
+static void smp_cond_relaxed_timeout_succeeds(struct kunit *test)
+{
+ struct task_struct *task;
+
+ flag = 0;
+
+ task = kthread_run(smp_cond_threadfn, &flag, "smp_cond_thread");
+
+ KUNIT_ASSERT_NOT_ERR_OR_NULL(test, task);
+ test_smp_cond_relaxed_timeout(test, &basic_clock, true);
+
+ kthread_stop(task);
+}
+
+static void smp_cond_relaxed_timeout_mocked(struct kunit *test)
+{
+ flag = 0;
+ test_smp_cond_relaxed_timeout(test, &mock_clock, true);
+}
+
+static void smp_cond_relaxed_timeout_expires(struct kunit *test)
+{
+ flag = 0;
+ test_smp_cond_relaxed_timeout(test, &basic_clock, false);
+}
+
+static struct kunit_case barrier_timeout_test_cases[] = {
+ KUNIT_CASE(smp_cond_relaxed_timeout_mocked),
+ KUNIT_CASE(smp_cond_relaxed_timeout_succeeds),
+ KUNIT_CASE(smp_cond_relaxed_timeout_expires),
+ {}
+};
+
+static struct kunit_suite barrier_timeout_test_suite = {
+ .name = "smp-cond-load-relaxed-timeout",
+ .test_cases = barrier_timeout_test_cases,
+};
+
+kunit_test_suite(barrier_timeout_test_suite);
+
+MODULE_DESCRIPTION("KUnit tests for smp_cond_load_relaxed_timeout()");
+MODULE_LICENSE("GPL");
--
2.31.1
^ permalink raw reply related
* [PATCH v11 13/14] kunit: enable testing smp_cond_load_relaxed_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
This enables the barrier tests to be built as a module.
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
arch/arm64/lib/delay.c | 2 ++
drivers/clocksource/arm_arch_timer.c | 2 ++
2 files changed, 4 insertions(+)
diff --git a/arch/arm64/lib/delay.c b/arch/arm64/lib/delay.c
index c660a7ea26dd..dfb102ce3009 100644
--- a/arch/arm64/lib/delay.c
+++ b/arch/arm64/lib/delay.c
@@ -12,6 +12,7 @@
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/timex.h>
+#include <kunit/visibility.h>
#include <asm/delay-const.h>
#include <clocksource/arm_arch_timer.h>
@@ -30,6 +31,7 @@ u64 notrace __delay_cycles(void)
guard(preempt_notrace)();
return __arch_counter_get_cntvct_stable();
}
+EXPORT_SYMBOL_IF_KUNIT(__delay_cycles);
void __delay(unsigned long cycles)
{
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 90aeff44a276..1de63e1a2cd2 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -28,6 +28,7 @@
#include <linux/acpi.h>
#include <linux/arm-smccc.h>
#include <linux/ptp_kvm.h>
+#include <kunit/visibility.h>
#include <asm/arch_timer.h>
#include <asm/virt.h>
@@ -896,6 +897,7 @@ bool arch_timer_evtstrm_available(void)
*/
return cpumask_test_cpu(raw_smp_processor_id(), &evtstrm_available);
}
+EXPORT_SYMBOL_IF_KUNIT(arch_timer_evtstrm_available);
static struct arch_timer_kvm_info arch_timer_kvm_info;
--
2.31.1
^ permalink raw reply related
* [PATCH v11 12/14] cpuidle/poll_state: Wait for need-resched via tif_need_resched_relaxed_wait()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
The inner loop in poll_idle() polls over the thread_info flags,
waiting to see if the thread has TIF_NEED_RESCHED set. The loop
exits once the condition is met, or if the poll time limit has
been exceeded.
To minimize the number of instructions executed in each iteration,
the time check is rate-limited. In addition, each loop iteration
executes cpu_relax() which on certain platforms provides a hint to
the pipeline that the loop busy-waits, allowing the processor to
reduce power consumption.
Switch over to tif_need_resched_relaxed_wait() instead, since that
provides exactly that.
However, since we want to minimize power consumption in idle, building
of cpuidle/poll_state.c continues to depend on CONFIG_ARCH_HAS_CPU_RELAX
as that serves as an indicator that the platform supports an optimized
version of tif_need_resched_relaxed_wait() (via
smp_cond_load_acquire_timeout()).
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-pm@vger.kernel.org
Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
drivers/cpuidle/poll_state.c | 21 +--------------------
1 file changed, 1 insertion(+), 20 deletions(-)
diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index c7524e4c522a..7443b3e971ba 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -6,41 +6,22 @@
#include <linux/cpuidle.h>
#include <linux/export.h>
#include <linux/irqflags.h>
-#include <linux/sched.h>
-#include <linux/sched/clock.h>
#include <linux/sched/idle.h>
#include <linux/sprintf.h>
#include <linux/types.h>
-#define POLL_IDLE_RELAX_COUNT 200
-
static int __cpuidle poll_idle(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int index)
{
- u64 time_start;
-
- time_start = local_clock_noinstr();
-
dev->poll_time_limit = false;
raw_local_irq_enable();
if (!current_set_polling_and_test()) {
- unsigned int loop_count = 0;
u64 limit;
limit = cpuidle_poll_time(drv, dev);
- while (!need_resched()) {
- cpu_relax();
- if (loop_count++ < POLL_IDLE_RELAX_COUNT)
- continue;
-
- loop_count = 0;
- if (local_clock_noinstr() - time_start > limit) {
- dev->poll_time_limit = true;
- break;
- }
- }
+ dev->poll_time_limit = !tif_need_resched_relaxed_wait(limit);
}
raw_local_irq_disable();
--
2.31.1
^ permalink raw reply related
* [PATCH v11 10/14] bpf/rqspinlock: Use smp_cond_load_acquire_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
Switch out the conditional load interfaces used by rqspinlock
to smp_cond_read_acquire_timeout() and its wrapper,
atomic_cond_read_acquire_timeout().
Both these handle the timeout and amortize as needed, so use the
non-amortized RES_CHECK_TIMEOUT.
RES_CHECK_TIMEOUT does double duty here -- presenting the current
clock value, the timeout/deadlock error from clock_deadlock() to
the cond-load and, returning the error value via ret.
For correctness, we need to ensure that the error case of the
cond-load interface always agrees with that in clock_deadlock().
For the most part, this is fine because there's no independent clock,
or double reads from the clock in cond-load -- either of which could
lead to its internal state going out of sync from that of
clock_deadlock().
There is, however, an edge case where clock_deadlock() checks for:
if (time > ts->timeout_end)
return -ETIMEDOUT;
while smp_cond_load_acquire_timeout() checks for:
__time_now = (time_expr_ns);
if (__time_now <= 0 || __time_now >= __time_end) {
VAL = READ_ONCE(*__PTR);
break;
}
This runs into a problem when (__time_now == __time_end) since
clock_deadlock() does not treat it as a timeout condition but
the second clause in the conditional above does.
So, add an equality check in clock_deadlock().
Finally, redefine SMP_TIMEOUT_POLL_COUNT to be 16k to be similar to
the spin-count used in the amortized version. We only do this for
non-arm64 as that uses a waiting implementation.
Cc: bpf@vger.kernel.org
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
kernel/bpf/rqspinlock.c | 40 +++++++++++++++++++++++-----------------
1 file changed, 23 insertions(+), 17 deletions(-)
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 0ec17ebb67c1..e5e27266b813 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -215,7 +215,7 @@ static noinline s64 clock_deadlock(rqspinlock_t *lock, u32 mask,
}
time = ktime_get_mono_fast_ns();
- if (time > ts->timeout_end)
+ if (time >= ts->timeout_end)
return -ETIMEDOUT;
/*
@@ -235,11 +235,10 @@ static noinline s64 clock_deadlock(rqspinlock_t *lock, u32 mask,
}
/*
- * Do not amortize with spins when res_smp_cond_load_acquire is defined,
- * as the macro does internal amortization for us.
+ * Spin amortized version of RES_CHECK_TIMEOUT. Used when busy-waiting in
+ * atomic_try_cmpxchg().
*/
-#ifndef res_smp_cond_load_acquire
-#define RES_CHECK_TIMEOUT(ts, ret, mask) \
+#define RES_CHECK_TIMEOUT_AMORTIZED(ts, ret, mask) \
({ \
s64 __timeval_err = 0; \
if (!(ts).spin++) \
@@ -247,7 +246,7 @@ static noinline s64 clock_deadlock(rqspinlock_t *lock, u32 mask,
(ret) = __timeval_err < 0 ? __timeval_err : 0; \
__timeval_err; \
})
-#else
+
#define RES_CHECK_TIMEOUT(ts, ret, mask) \
({ \
s64 __timeval_err; \
@@ -255,7 +254,6 @@ static noinline s64 clock_deadlock(rqspinlock_t *lock, u32 mask,
(ret) = __timeval_err < 0 ? __timeval_err : 0; \
__timeval_err; \
})
-#endif
/*
* Initialize the 'spin' member.
@@ -269,6 +267,17 @@ static noinline s64 clock_deadlock(rqspinlock_t *lock, u32 mask,
*/
#define RES_RESET_TIMEOUT(ts, _duration) ({ (ts).timeout_end = 0; (ts).duration = _duration; })
+/*
+ * Limit how often we invoke clock_deadlock() while spin-waiting in
+ * smp_cond_load_acquire_timeout() or atomic_cond_read_acquire_timeout().
+ *
+ * We only override the default value not superceding ARM64's override.
+ */
+#ifndef CONFIG_ARM64
+#undef SMP_TIMEOUT_POLL_COUNT
+#define SMP_TIMEOUT_POLL_COUNT (16*1024)
+#endif
+
/*
* Provide a test-and-set fallback for cases when queued spin lock support is
* absent from the architecture.
@@ -296,7 +305,7 @@ int __lockfunc resilient_tas_spin_lock(rqspinlock_t *lock)
val = atomic_read(&lock->val);
if (val || !atomic_try_cmpxchg(&lock->val, &val, 1)) {
- if (RES_CHECK_TIMEOUT(ts, ret, ~0u) < 0)
+ if (RES_CHECK_TIMEOUT_AMORTIZED(ts, ret, ~0u) < 0)
goto out;
cpu_relax();
goto retry;
@@ -319,12 +328,6 @@ EXPORT_SYMBOL_GPL(resilient_tas_spin_lock);
*/
static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
-#ifndef res_smp_cond_load_acquire
-#define res_smp_cond_load_acquire(v, c) smp_cond_load_acquire(v, c)
-#endif
-
-#define res_atomic_cond_read_acquire(v, c) res_smp_cond_load_acquire(&(v)->counter, (c))
-
/**
* resilient_queued_spin_lock_slowpath - acquire the queued spinlock
* @lock: Pointer to queued spinlock structure
@@ -421,7 +424,9 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
*/
if (val & _Q_LOCKED_MASK) {
RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT);
- res_smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_MASK) < 0);
+ smp_cond_load_acquire_timeout(&lock->locked, !VAL,
+ RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_MASK),
+ ts.duration);
}
if (ret) {
@@ -582,8 +587,9 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
* us.
*/
RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT * 2);
- val = res_atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK) ||
- RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_PENDING_MASK) < 0);
+ val = atomic_cond_read_acquire_timeout(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK),
+ RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_PENDING_MASK),
+ ts.duration);
/* Disable queue destruction when we detect deadlocks. */
if (ret == -EDEADLK) {
--
2.31.1
^ permalink raw reply related
* [PATCH v11 08/14] locking/atomic: scripts: build atomic_long_cond_read_*_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora, Boqun Feng
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
Add the atomic long wrappers for the cond-load timeout interfaces.
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
include/linux/atomic/atomic-long.h | 18 +++++++++++-------
scripts/atomic/gen-atomic-long.sh | 16 ++++++++++------
2 files changed, 21 insertions(+), 13 deletions(-)
diff --git a/include/linux/atomic/atomic-long.h b/include/linux/atomic/atomic-long.h
index 6a4e47d2db35..553b6b0e0258 100644
--- a/include/linux/atomic/atomic-long.h
+++ b/include/linux/atomic/atomic-long.h
@@ -11,14 +11,18 @@
#ifdef CONFIG_64BIT
typedef atomic64_t atomic_long_t;
-#define ATOMIC_LONG_INIT(i) ATOMIC64_INIT(i)
-#define atomic_long_cond_read_acquire atomic64_cond_read_acquire
-#define atomic_long_cond_read_relaxed atomic64_cond_read_relaxed
+#define ATOMIC_LONG_INIT(i) ATOMIC64_INIT(i)
+#define atomic_long_cond_read_acquire atomic64_cond_read_acquire
+#define atomic_long_cond_read_relaxed atomic64_cond_read_relaxed
+#define atomic_long_cond_read_acquire_timeout atomic64_cond_read_acquire_timeout
+#define atomic_long_cond_read_relaxed_timeout atomic64_cond_read_relaxed_timeout
#else
typedef atomic_t atomic_long_t;
-#define ATOMIC_LONG_INIT(i) ATOMIC_INIT(i)
-#define atomic_long_cond_read_acquire atomic_cond_read_acquire
-#define atomic_long_cond_read_relaxed atomic_cond_read_relaxed
+#define ATOMIC_LONG_INIT(i) ATOMIC_INIT(i)
+#define atomic_long_cond_read_acquire atomic_cond_read_acquire
+#define atomic_long_cond_read_relaxed atomic_cond_read_relaxed
+#define atomic_long_cond_read_acquire_timeout atomic_cond_read_acquire_timeout
+#define atomic_long_cond_read_relaxed_timeout atomic_cond_read_relaxed_timeout
#endif
/**
@@ -1809,4 +1813,4 @@ raw_atomic_long_dec_if_positive(atomic_long_t *v)
}
#endif /* _LINUX_ATOMIC_LONG_H */
-// 4b882bf19018602c10816c52f8b4ae280adc887b
+// 79c1f4acb5774376ceed559843d5d9ed1348df99
diff --git a/scripts/atomic/gen-atomic-long.sh b/scripts/atomic/gen-atomic-long.sh
index 9826be3ba986..874643dc74bd 100755
--- a/scripts/atomic/gen-atomic-long.sh
+++ b/scripts/atomic/gen-atomic-long.sh
@@ -79,14 +79,18 @@ cat << EOF
#ifdef CONFIG_64BIT
typedef atomic64_t atomic_long_t;
-#define ATOMIC_LONG_INIT(i) ATOMIC64_INIT(i)
-#define atomic_long_cond_read_acquire atomic64_cond_read_acquire
-#define atomic_long_cond_read_relaxed atomic64_cond_read_relaxed
+#define ATOMIC_LONG_INIT(i) ATOMIC64_INIT(i)
+#define atomic_long_cond_read_acquire atomic64_cond_read_acquire
+#define atomic_long_cond_read_relaxed atomic64_cond_read_relaxed
+#define atomic_long_cond_read_acquire_timeout atomic64_cond_read_acquire_timeout
+#define atomic_long_cond_read_relaxed_timeout atomic64_cond_read_relaxed_timeout
#else
typedef atomic_t atomic_long_t;
-#define ATOMIC_LONG_INIT(i) ATOMIC_INIT(i)
-#define atomic_long_cond_read_acquire atomic_cond_read_acquire
-#define atomic_long_cond_read_relaxed atomic_cond_read_relaxed
+#define ATOMIC_LONG_INIT(i) ATOMIC_INIT(i)
+#define atomic_long_cond_read_acquire atomic_cond_read_acquire
+#define atomic_long_cond_read_relaxed atomic_cond_read_relaxed
+#define atomic_long_cond_read_acquire_timeout atomic_cond_read_acquire_timeout
+#define atomic_long_cond_read_relaxed_timeout atomic_cond_read_relaxed_timeout
#endif
EOF
--
2.31.1
^ permalink raw reply related
* [PATCH v11 07/14] atomic: Add atomic_cond_read_*_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora, Boqun Feng
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
Add atomic load wrappers, atomic_cond_read_*_timeout() and
atomic64_cond_read_*_timeout() for the cond-load timeout interfaces.
Also add a short description for the atomic_cond_read_{relaxed,acquire}(),
and the atomic_cond_read_{relaxed,acquire}_timeout() interfaces.
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
Documentation/atomic_t.txt | 14 +++++++++-----
include/linux/atomic.h | 10 ++++++++++
2 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
index bee3b1bca9a7..0e53f6ccb558 100644
--- a/Documentation/atomic_t.txt
+++ b/Documentation/atomic_t.txt
@@ -16,6 +16,10 @@ Non-RMW ops:
atomic_read(), atomic_set()
atomic_read_acquire(), atomic_set_release()
+Non-RMW, non-atomic_t ops:
+
+ atomic_cond_read_{relaxed,acquire}()
+ atomic_cond_read_{relaxed,acquire}_timeout()
RMW atomic operations:
@@ -79,11 +83,11 @@ SEMANTICS
Non-RMW ops:
-The non-RMW ops are (typically) regular LOADs and STOREs and are canonically
-implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and
-smp_store_release() respectively. Therefore, if you find yourself only using
-the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all
-and are doing it wrong.
+The non-RMW ops are (typically) regular, or conditional LOADs and STOREs and
+are canonically implemented using READ_ONCE(), WRITE_ONCE(),
+smp_load_acquire() and smp_store_release() respectively. Therefore, if you
+find yourself only using the Non-RMW operations of atomic_t, you do not in
+fact need atomic_t at all and are doing it wrong.
A note for the implementation of atomic_set{}() is that it must not break the
atomicity of the RMW ops. That is:
diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index 8dd57c3a99e9..5bcb86e07784 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -31,6 +31,16 @@
#define atomic64_cond_read_acquire(v, c) smp_cond_load_acquire(&(v)->counter, (c))
#define atomic64_cond_read_relaxed(v, c) smp_cond_load_relaxed(&(v)->counter, (c))
+#define atomic_cond_read_acquire_timeout(v, c, e, t) \
+ smp_cond_load_acquire_timeout(&(v)->counter, (c), (e), (t))
+#define atomic_cond_read_relaxed_timeout(v, c, e, t) \
+ smp_cond_load_relaxed_timeout(&(v)->counter, (c), (e), (t))
+
+#define atomic64_cond_read_acquire_timeout(v, c, e, t) \
+ smp_cond_load_acquire_timeout(&(v)->counter, (c), (e), (t))
+#define atomic64_cond_read_relaxed_timeout(v, c, e, t) \
+ smp_cond_load_relaxed_timeout(&(v)->counter, (c), (e), (t))
+
/*
* The idea here is to build acquire/release variants by adding explicit
* barriers on top of the relaxed variant. In the case where the relaxed
--
2.31.1
^ permalink raw reply related
* [PATCH v11 05/14] arm64: rqspinlock: Remove private copy of smp_cond_load_acquire_timewait()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
In preparation for defining smp_cond_load_acquire_timeout(), remove
the private copy. Lacking this, the rqspinlock code falls back to using
smp_cond_load_acquire().
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: bpf@vger.kernel.org
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Haris Okanovic <harisokn@amazon.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
arch/arm64/include/asm/rqspinlock.h | 85 -----------------------------
1 file changed, 85 deletions(-)
diff --git a/arch/arm64/include/asm/rqspinlock.h b/arch/arm64/include/asm/rqspinlock.h
index 9ea0a74e5892..a385603436e9 100644
--- a/arch/arm64/include/asm/rqspinlock.h
+++ b/arch/arm64/include/asm/rqspinlock.h
@@ -3,91 +3,6 @@
#define _ASM_RQSPINLOCK_H
#include <asm/barrier.h>
-
-/*
- * Hardcode res_smp_cond_load_acquire implementations for arm64 to a custom
- * version based on [0]. In rqspinlock code, our conditional expression involves
- * checking the value _and_ additionally a timeout. However, on arm64, the
- * WFE-based implementation may never spin again if no stores occur to the
- * locked byte in the lock word. As such, we may be stuck forever if
- * event-stream based unblocking is not available on the platform for WFE spin
- * loops (arch_timer_evtstrm_available).
- *
- * Once support for smp_cond_load_acquire_timewait [0] lands, we can drop this
- * copy-paste.
- *
- * While we rely on the implementation to amortize the cost of sampling
- * cond_expr for us, it will not happen when event stream support is
- * unavailable, time_expr check is amortized. This is not the common case, and
- * it would be difficult to fit our logic in the time_expr_ns >= time_limit_ns
- * comparison, hence just let it be. In case of event-stream, the loop is woken
- * up at microsecond granularity.
- *
- * [0]: https://lore.kernel.org/lkml/20250203214911.898276-1-ankur.a.arora@oracle.com
- */
-
-#ifndef smp_cond_load_acquire_timewait
-
-#define smp_cond_time_check_count 200
-
-#define __smp_cond_load_relaxed_spinwait(ptr, cond_expr, time_expr_ns, \
- time_limit_ns) ({ \
- typeof(ptr) __PTR = (ptr); \
- __unqual_scalar_typeof(*ptr) VAL; \
- unsigned int __count = 0; \
- for (;;) { \
- VAL = READ_ONCE(*__PTR); \
- if (cond_expr) \
- break; \
- cpu_relax(); \
- if (__count++ < smp_cond_time_check_count) \
- continue; \
- if ((time_expr_ns) >= (time_limit_ns)) \
- break; \
- __count = 0; \
- } \
- (typeof(*ptr))VAL; \
-})
-
-#define __smp_cond_load_acquire_timewait(ptr, cond_expr, \
- time_expr_ns, time_limit_ns) \
-({ \
- typeof(ptr) __PTR = (ptr); \
- __unqual_scalar_typeof(*ptr) VAL; \
- for (;;) { \
- VAL = smp_load_acquire(__PTR); \
- if (cond_expr) \
- break; \
- __cmpwait_relaxed(__PTR, VAL); \
- if ((time_expr_ns) >= (time_limit_ns)) \
- break; \
- } \
- (typeof(*ptr))VAL; \
-})
-
-#define smp_cond_load_acquire_timewait(ptr, cond_expr, \
- time_expr_ns, time_limit_ns) \
-({ \
- __unqual_scalar_typeof(*ptr) _val; \
- int __wfe = arch_timer_evtstrm_available(); \
- \
- if (likely(__wfe)) { \
- _val = __smp_cond_load_acquire_timewait(ptr, cond_expr, \
- time_expr_ns, \
- time_limit_ns); \
- } else { \
- _val = __smp_cond_load_relaxed_spinwait(ptr, cond_expr, \
- time_expr_ns, \
- time_limit_ns); \
- smp_acquire__after_ctrl_dep(); \
- } \
- (typeof(*ptr))_val; \
-})
-
-#endif
-
-#define res_smp_cond_load_acquire(v, c) smp_cond_load_acquire_timewait(v, c, 0, 1)
-
#include <asm-generic/rqspinlock.h>
#endif /* _ASM_RQSPINLOCK_H */
--
2.31.1
^ permalink raw reply related
* [PATCH v11 06/14] asm-generic: barrier: Add smp_cond_load_acquire_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
Add the acquire variant of smp_cond_load_relaxed_timeout(). This
reuses the relaxed variant, with additional LOAD->LOAD ordering.
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-arch@vger.kernel.org
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Haris Okanovic <harisokn@amazon.com>
Tested-by: Haris Okanovic <harisokn@amazon.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
include/asm-generic/barrier.h | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index e5a6a1c04649..68d9e7108f4a 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -342,6 +342,32 @@ do { \
})
#endif
+/**
+ * smp_cond_load_acquire_timeout() - (Spin) wait for cond with ACQUIRE ordering
+ * until a timeout expires.
+ * @ptr: pointer to the variable to wait on.
+ * @cond_expr: boolean expression to wait for.
+ * @time_expr_ns: monotonic expression that evaluates to time in ns or,
+ * on failure, returns a negative value.
+ * @timeout_ns: timeout value in ns
+ * (Both of the above are assumed to be compatible with s64.)
+ *
+ * Equivalent to using smp_cond_load_acquire() on the condition variable with
+ * a timeout.
+ */
+#ifndef smp_cond_load_acquire_timeout
+#define smp_cond_load_acquire_timeout(ptr, cond_expr, \
+ time_expr_ns, timeout_ns) \
+({ \
+ __unqual_scalar_typeof(*ptr) _val; \
+ _val = smp_cond_load_relaxed_timeout(ptr, cond_expr, \
+ time_expr_ns, \
+ timeout_ns); \
+ smp_acquire__after_ctrl_dep(); \
+ (typeof(*ptr))_val; \
+})
+#endif
+
/*
* pmem_wmb() ensures that all stores for which the modification
* are written to persistent storage by preceding instructions have
--
2.31.1
^ permalink raw reply related
* [PATCH v11 04/14] arm64: support WFET in smp_cond_load_relaxed_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
To handle WFET use __cmpwait_timeout() similarly to __cmpwait(). These
call out to the respective __cmpwait_case_timeout_##sz(),
__cmpwait_case_##sz() functions.
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
arch/arm64/include/asm/barrier.h | 8 +++--
arch/arm64/include/asm/cmpxchg.h | 62 +++++++++++++++++++++++++-------
2 files changed, 55 insertions(+), 15 deletions(-)
diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 6190e178db51..fbd71cd4ef4e 100644
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -224,8 +224,8 @@ do { \
extern bool arch_timer_evtstrm_available(void);
/*
- * In the common case, cpu_poll_relax() sits waiting in __cmpwait_relaxed()
- * for the ptr value to change.
+ * In the common case, cpu_poll_relax() sits waiting in __cmpwait_relaxed()/
+ * __cmpwait_relaxed_timeout() for the ptr value to change.
*
* Since this period is reasonably long, choose SMP_TIMEOUT_POLL_COUNT
* to be 1, so smp_cond_load_{relaxed,acquire}_timeout() does a
@@ -234,7 +234,9 @@ extern bool arch_timer_evtstrm_available(void);
#define SMP_TIMEOUT_POLL_COUNT 1
#define cpu_poll_relax(ptr, val, timeout_ns) do { \
- if (arch_timer_evtstrm_available()) \
+ if (alternative_has_cap_unlikely(ARM64_HAS_WFXT)) \
+ __cmpwait_relaxed_timeout(ptr, val, timeout_ns); \
+ else if (arch_timer_evtstrm_available()) \
__cmpwait_relaxed(ptr, val); \
else \
cpu_relax(); \
diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h
index 6cf3cd6873f5..9e4cdc9e41d1 100644
--- a/arch/arm64/include/asm/cmpxchg.h
+++ b/arch/arm64/include/asm/cmpxchg.h
@@ -12,6 +12,7 @@
#include <asm/barrier.h>
#include <asm/lse.h>
+#include <asm/delay-const.h>
/*
* We need separate acquire parameters for ll/sc and lse, since the full
@@ -212,7 +213,8 @@ __CMPXCHG_GEN(_mb)
#define __CMPWAIT_CASE(w, sfx, sz) \
static inline void __cmpwait_case_##sz(volatile void *ptr, \
- unsigned long val) \
+ unsigned long val, \
+ u64 __maybe_unused timeout_ns) \
{ \
unsigned long tmp; \
\
@@ -235,20 +237,52 @@ __CMPWAIT_CASE( , , 64);
#undef __CMPWAIT_CASE
-#define __CMPWAIT_GEN(sfx) \
-static __always_inline void __cmpwait##sfx(volatile void *ptr, \
- unsigned long val, \
- int size) \
+#define __CMPWAIT_TIMEOUT_CASE(w, sfx, sz) \
+static inline void __cmpwait_case_timeout_##sz(volatile void *ptr, \
+ unsigned long val, \
+ u64 timeout_ns) \
+{ \
+ unsigned long tmp; \
+ u64 ecycles = __delay_cycles() + \
+ NSECS_TO_CYCLES(timeout_ns); \
+ asm volatile( \
+ " sevl\n" \
+ " wfe\n" \
+ " ldxr" #sfx "\t%" #w "[tmp], %[v]\n" \
+ " eor %" #w "[tmp], %" #w "[tmp], %" #w "[val]\n" \
+ " cbnz %" #w "[tmp], 2f\n" \
+ " msr s0_3_c1_c0_0, %[ecycles]\n" \
+ "2:" \
+ : [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr) \
+ : [val] "r" (val), [ecycles] "r" (ecycles)); \
+}
+
+__CMPWAIT_TIMEOUT_CASE(w, b, 8);
+__CMPWAIT_TIMEOUT_CASE(w, h, 16);
+__CMPWAIT_TIMEOUT_CASE(w, , 32);
+__CMPWAIT_TIMEOUT_CASE( , , 64);
+
+#undef __CMPWAIT_TIMEOUT_CASE
+
+#define __CMPWAIT_GEN(timeout, sfx) \
+static __always_inline void __cmpwait##timeout##sfx(volatile void *ptr, \
+ unsigned long val, \
+ u64 timeout_ns, \
+ int size) \
{ \
switch (size) { \
case 1: \
- return __cmpwait_case##sfx##_8(ptr, (u8)val); \
+ return __cmpwait_case##timeout##sfx##_8(ptr, (u8)val, \
+ timeout_ns); \
case 2: \
- return __cmpwait_case##sfx##_16(ptr, (u16)val); \
+ return __cmpwait_case##timeout##sfx##_16(ptr, (u16)val, \
+ timeout_ns); \
case 4: \
- return __cmpwait_case##sfx##_32(ptr, val); \
+ return __cmpwait_case##timeout##sfx##_32(ptr, val, \
+ timeout_ns); \
case 8: \
- return __cmpwait_case##sfx##_64(ptr, val); \
+ return __cmpwait_case##timeout##sfx##_64(ptr, val, \
+ timeout_ns); \
default: \
BUILD_BUG(); \
} \
@@ -256,11 +290,15 @@ static __always_inline void __cmpwait##sfx(volatile void *ptr, \
unreachable(); \
}
-__CMPWAIT_GEN()
+__CMPWAIT_GEN( , )
+__CMPWAIT_GEN(_timeout, )
#undef __CMPWAIT_GEN
-#define __cmpwait_relaxed(ptr, val) \
- __cmpwait((ptr), (unsigned long)(val), sizeof(*(ptr)))
+#define __cmpwait_relaxed_timeout(ptr, val, timeout_ns) \
+ __cmpwait_timeout((ptr), (unsigned long)(val), timeout_ns, sizeof(*(ptr)))
+
+#define __cmpwait_relaxed(ptr, val) \
+ __cmpwait((ptr), (unsigned long)(val), 0, sizeof(*(ptr)))
#endif /* __ASM_CMPXCHG_H */
--
2.31.1
^ permalink raw reply related
* [PATCH v11 03/14] arm64/delay: move some constants out to a separate header
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora, Bjorn Andersson,
Konrad Dybcio, Christoph Lameter
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
Moves some constants and functions related to xloops, cycles computation
out to a new header. Also make __delay_cycles() available outside of
arch/arm64/lib/delay.c.
Rename some macros in qcom/rpmh-rsc.c which were occupying the same
namespace.
No functional change.
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Bjorn Andersson <andersson@kernel.org>
Cc: Konrad Dybcio <konradybcio@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Reviewed-by: Christoph Lameter <cl@linux.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
arch/arm64/include/asm/delay-const.h | 27 +++++++++++++++++++++++++++
arch/arm64/lib/delay.c | 15 ++++-----------
drivers/soc/qcom/rpmh-rsc.c | 8 ++++----
3 files changed, 35 insertions(+), 15 deletions(-)
create mode 100644 arch/arm64/include/asm/delay-const.h
diff --git a/arch/arm64/include/asm/delay-const.h b/arch/arm64/include/asm/delay-const.h
new file mode 100644
index 000000000000..cb3988ff4e41
--- /dev/null
+++ b/arch/arm64/include/asm/delay-const.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _ASM_DELAY_CONST_H
+#define _ASM_DELAY_CONST_H
+
+#include <asm/param.h> /* For HZ */
+
+/* 2**32 / 1000000 (rounded up) */
+#define __usecs_to_xloops_mult 0x10C7UL
+
+/* 2**32 / 1000000000 (rounded up) */
+#define __nsecs_to_xloops_mult 0x5UL
+
+extern unsigned long loops_per_jiffy;
+static inline unsigned long xloops_to_cycles(unsigned long xloops)
+{
+ return (xloops * loops_per_jiffy * HZ) >> 32;
+}
+
+#define USECS_TO_CYCLES(time_usecs) \
+ xloops_to_cycles((time_usecs) * __usecs_to_xloops_mult)
+
+#define NSECS_TO_CYCLES(time_nsecs) \
+ xloops_to_cycles((time_nsecs) * __nsecs_to_xloops_mult)
+
+u64 notrace __delay_cycles(void);
+
+#endif /* _ASM_DELAY_CONST_H */
diff --git a/arch/arm64/lib/delay.c b/arch/arm64/lib/delay.c
index e278e060e78a..c660a7ea26dd 100644
--- a/arch/arm64/lib/delay.c
+++ b/arch/arm64/lib/delay.c
@@ -12,17 +12,10 @@
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/timex.h>
+#include <asm/delay-const.h>
#include <clocksource/arm_arch_timer.h>
-#define USECS_TO_CYCLES(time_usecs) \
- xloops_to_cycles((time_usecs) * 0x10C7UL)
-
-static inline unsigned long xloops_to_cycles(unsigned long xloops)
-{
- return (xloops * loops_per_jiffy * HZ) >> 32;
-}
-
/*
* Force the use of CNTVCT_EL0 in order to have the same base as WFxT.
* This avoids some annoying issues when CNTVOFF_EL2 is not reset 0 on a
@@ -32,7 +25,7 @@ static inline unsigned long xloops_to_cycles(unsigned long xloops)
* Note that userspace cannot change the offset behind our back either,
* as the vcpu mutex is held as long as KVM_RUN is in progress.
*/
-static cycles_t notrace __delay_cycles(void)
+u64 notrace __delay_cycles(void)
{
guard(preempt_notrace)();
return __arch_counter_get_cntvct_stable();
@@ -73,12 +66,12 @@ EXPORT_SYMBOL(__const_udelay);
void __udelay(unsigned long usecs)
{
- __const_udelay(usecs * 0x10C7UL); /* 2**32 / 1000000 (rounded up) */
+ __const_udelay(usecs * __usecs_to_xloops_mult);
}
EXPORT_SYMBOL(__udelay);
void __ndelay(unsigned long nsecs)
{
- __const_udelay(nsecs * 0x5UL); /* 2**32 / 1000000000 (rounded up) */
+ __const_udelay(nsecs * __nsecs_to_xloops_mult);
}
EXPORT_SYMBOL(__ndelay);
diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
index c6f7d5c9c493..ad5ec5c0de0a 100644
--- a/drivers/soc/qcom/rpmh-rsc.c
+++ b/drivers/soc/qcom/rpmh-rsc.c
@@ -146,10 +146,10 @@ enum {
* +---------------------------------------------------+
*/
-#define USECS_TO_CYCLES(time_usecs) \
- xloops_to_cycles((time_usecs) * 0x10C7UL)
+#define RPMH_USECS_TO_CYCLES(time_usecs) \
+ rpmh_xloops_to_cycles((time_usecs) * 0x10C7UL)
-static inline unsigned long xloops_to_cycles(u64 xloops)
+static inline unsigned long rpmh_xloops_to_cycles(u64 xloops)
{
return (xloops * loops_per_jiffy * HZ) >> 32;
}
@@ -819,7 +819,7 @@ void rpmh_rsc_write_next_wakeup(struct rsc_drv *drv)
wakeup_us = ktime_to_us(wakeup);
/* Convert the wakeup to arch timer scale */
- wakeup_cycles = USECS_TO_CYCLES(wakeup_us);
+ wakeup_cycles = RPMH_USECS_TO_CYCLES(wakeup_us);
wakeup_cycles += arch_timer_read_counter();
exit:
--
2.31.1
^ permalink raw reply related
* [PATCH v11 00/14] barrier: Add smp_cond_load_{relaxed,acquire}_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
Hi,
Main change in this version:
- adds a kunit validation test.
What remains?:
- Review by PeterZ of the new interface tif_need_resched_relaxed_wait()
(patch 11, "sched: add need-resched timed wait interface").
(Peter had originally proposed using smp_cond_load_relaxed() in
poll_idle() [11]).
The core kernel often uses smp_cond_load_{relaxed,acquire}() to spin
on condition variables with architectural primitives used to avoid
hammering the relevant cachelines.
(This primitive can vary greatly across architectures: on x86 it's a
cpu_relax() to slow down the pipeline. On arm64, this is a __cmpwait()
which waits for a cacheline to change state in a time limited fashion.)
Regardless of architectural details, typical smp_cond_load*() usage
does not allow for termination until the condition change occurs.
Beyond the core kernel, there are cases where it is useful to additionally
terminate on a timeout. Two cases:
- cpuidle poll_idle(): wait for need-resched until the cpuidle polling
duration expires.
- rqspinlock: nested qspinlock acquisition that terminates on timeout
or deadlock.
Accordingly add two interfaces (with their generic and arm64 specific
implementations):
smp_cond_load_relaxed_timeout(ptr, cond_expr, time_expr, timeout)
smp_cond_load_acquire_timeout(ptr, cond_expr, time_expr, timeout)
Also add tif_need_resched_relaxed_wait() which wraps the polling
pattern and its scheduler specific details in poll_idle().
In addition add atomic_cond_read_*_timeout(),
atomic64_cond_read_*_timeout(), and atomic_long wrappers.
Structurally, both the smp_cond_load_*_timeout() interfaces are similar
to smp_cond_load*(), with the addition of a rate-limited time-check.
Usage
==
These interfaces drop straight-forwardly into the rqspinlock logic
since qspinlock already uses smp_cond_load*(), and the time-check
extension can now be used for timeout and deadlock handling.
Using tif_need_resched_relaxed_wait() in poll_idle() removes any
architectural details allowing arm64 to straight-forwardly support
that path.
(However, for efficiency reasons cpuidle/poll_state.c continues to
depend on ARCH_HAS_CPU_RELAX since that is defined on architectures
with an optimized architectural primitive.)
Performance
==
Apart from simplifications due to this change, supporting polling in
cpuidle on arm64 helps improve wakeup latency (needs a few cpuidle/acpi
patches):
# perf stat -r 5 --cpu 4,5 -e task-clock,cycles,instructions,sched:sched_wake_idle_without_ipi \
perf bench sched pipe -l 1000000 -c 4
# No haltpoll (and, no TIF_POLLING_NRFLAG):
Performance counter stats for 'CPU(s) 4,5' (5 runs):
25,229.57 msec task-clock # 2.000 CPUs utilized ( +- 7.75% )
45,821,250,284 cycles # 1.816 GHz ( +- 10.07% )
26,557,496,665 instructions # 0.58 insn per cycle ( +- 0.21% )
0 sched:sched_wake_idle_without_ipi # 0.000 /sec
12.615 +- 0.977 seconds time elapsed ( +- 7.75% )
# Haltpoll:
Performance counter stats for 'CPU(s) 4,5' (5 runs):
15,131.58 msec task-clock # 2.000 CPUs utilized ( +- 10.00% )
34,158,188,839 cycles # 2.257 GHz ( +- 6.91% )
20,824,950,916 instructions # 0.61 insn per cycle ( +- 0.09% )
1,983,822 sched:sched_wake_idle_without_ipi # 131.105 K/sec ( +- 0.78% )
7.566 +- 0.756 seconds time elapsed ( +- 10.00% )
We get improved latency because we don't switch in and out of a
deeper sleep state or from the hypervisor. This also causes us to
execute ~20% fewer instructions.
Haris Okanovic also saw improvement in real workloads due to the
cpuidle changes: "observed 4-6% improvements in memcahed, cassandra,
mysql, and postgresql under certain loads. Other applications likely
benefit too." [12]
Changelog:
v10 [10]:
- add a comment mentioning that smp_cond_load_relaxed_timeout() might
be using architectural primitives that don't support MMIO.
(David Laight, Catalin Marinas)
- added a kunit test for smp_cond_load_relaxed_timeout() (Andrew
Morton.)
v9 [9]:
- s/@cond/@cond_expr/ (Randy Dunlap)
- Clarify that SMP_TIMEOUT_POLL_COUNT is only around memory
addresses. (David Laight)
- Add the missing config ARCH_HAS_CPU_RELAX in arch/arm64/Kconfig.
(Catalin Marinas).
- Switch to arch_counter_get_cntvct_stable() (via __delay_cycles())
in the cmpwait path instead of using arch_timer_read_counter().
(Catalin Marinas)
v8 [0]:
- Defer evaluation of @time_expr_ns to when we hit the slowpath.
(comment from Alexei Starovoitov).
- Mention that cpu_poll_relax() is better than raw CPU polling
only where ARCH_HAS_CPU_RELAX is defined.
- also define ARCH_HAS_CPU_RELAX for arm64.
(Came out of a discussion with Will Deacon.)
- Split out WFET and WFE handling. I was doing both of these
in a common handler.
(From Will Deacon and in an earlier revision by Catalin Marinas.)
- Add mentions of atomic_cond_read_{relaxed,acquire}(),
atomic_cond_read_{relaxed,acquire}_timeout() in
Documentation/atomic_t.txt.
- Use the BIT() macro to do the checking in tif_bitset_relaxed_wait().
- Cleanup unnecessary assignments, casts etc in poll_idle().
(From Rafael Wysocki.)
- Fixup warnings from kernel build robot
v7 [1]:
- change the interface to separately provide the timeout. This is
useful for supporting WFET and similar primitives which can do
timed waiting (suggested by Arnd Bergmann).
- Adapting rqspinlock code to this changed interface also
necessitated allowing time_expr to fail.
- rqspinlock changes to adapt to the new smp_cond_load_acquire_timeout().
- add WFET support (suggested by Arnd Bergmann).
- add support for atomic-long wrappers.
- add a new scheduler interface tif_need_resched_relaxed_wait() which
encapsulates the polling logic used by poll_idle().
- interface suggested by (Rafael J. Wysocki).
v6 [2]:
- fixup missing timeout parameters in atomic64_cond_read_*_timeout()
- remove a race between setting of TIF_NEED_RESCHED and the call to
smp_cond_load_relaxed_timeout(). This would mean that dev->poll_time_limit
would be set even if we hadn't spent any time waiting.
(The original check compared against local_clock(), which would have been
fine, but I was instead using a cheaper check against _TIF_NEED_RESCHED.)
(Both from meta-CI bot)
v5 [3]:
- use cpu_poll_relax() instead of cpu_relax().
- instead of defining an arm64 specific
smp_cond_load_relaxed_timeout(), just define the appropriate
cpu_poll_relax().
- re-read the target pointer when we exit due to the time-check.
- s/SMP_TIMEOUT_SPIN_COUNT/SMP_TIMEOUT_POLL_COUNT/
(Suggested by Will Deacon)
- add atomic_cond_read_*_timeout() and atomic64_cond_read_*_timeout()
interfaces.
- rqspinlock: use atomic_cond_read_acquire_timeout().
- cpuidle: use smp_cond_load_relaxed_tiemout() for polling.
(Suggested by Catalin Marinas)
- rqspinlock: define SMP_TIMEOUT_POLL_COUNT to be 16k for non arm64
v4 [4]:
- naming change 's/timewait/timeout/'
- resilient spinlocks: get rid of res_smp_cond_load_acquire_waiting()
and fixup use of RES_CHECK_TIMEOUT().
(Both suggested by Catalin Marinas)
v3 [5]:
- further interface simplifications (suggested by Catalin Marinas)
v2 [6]:
- simplified the interface (suggested by Catalin Marinas)
- get rid of wait_policy, and a multitude of constants
- adds a slack parameter
This helped remove a fair amount of duplicated code duplication and in
hindsight unnecessary constants.
v1 [7]:
- add wait_policy (coarse and fine)
- derive spin-count etc at runtime instead of using arbitrary
constants.
Haris Okanovic tested v4 of this series with poll_idle()/haltpoll patches. [8]
Comments appreciated!
Thanks
Ankur
[0] https://lore.kernel.org/lkml/20251215044919.460086-1-ankur.a.arora@oracle.com/
[1] https://lore.kernel.org/lkml/20251028053136.692462-1-ankur.a.arora@oracle.com/
[2] https://lore.kernel.org/lkml/20250911034655.3916002-1-ankur.a.arora@oracle.com/
[3] https://lore.kernel.org/lkml/20250911034655.3916002-1-ankur.a.arora@oracle.com/
[4] https://lore.kernel.org/lkml/20250829080735.3598416-1-ankur.a.arora@oracle.com/
[5] https://lore.kernel.org/lkml/20250627044805.945491-1-ankur.a.arora@oracle.com/
[6] https://lore.kernel.org/lkml/20250502085223.1316925-1-ankur.a.arora@oracle.com/
[7] https://lore.kernel.org/lkml/20250203214911.898276-1-ankur.a.arora@oracle.com/
[8] https://lore.kernel.org/lkml/2cecbf7fb23ee83a4ce027e1be3f46f97efd585c.camel@amazon.com/
[9] https://lore.kernel.org/lkml/20260209023153.2661784-1-ankur.a.arora@oracle.com/
[10] https://lore.kernel.org/lkml/20260316013651.3225328-1-ankur.a.arora@oracle.com/
[11] https://lore.kernel.org/lkml/20230809134837.GM212435@hirez.programming.kicks-ass.net/
[12] https://lore.kernel.org/lkml/c6f3c8d3f1f2e89a9dc7ae22482973b5a51b08cb.camel@amazon.com/
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: bpf@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-pm@vger.kernel.org
Ankur Arora (14):
asm-generic: barrier: Add smp_cond_load_relaxed_timeout()
arm64: barrier: Support smp_cond_load_relaxed_timeout()
arm64/delay: move some constants out to a separate header
arm64: support WFET in smp_cond_load_relaxed_timeout()
arm64: rqspinlock: Remove private copy of
smp_cond_load_acquire_timewait()
asm-generic: barrier: Add smp_cond_load_acquire_timeout()
atomic: Add atomic_cond_read_*_timeout()
locking/atomic: scripts: build atomic_long_cond_read_*_timeout()
bpf/rqspinlock: switch check_timeout() to a clock interface
bpf/rqspinlock: Use smp_cond_load_acquire_timeout()
sched: add need-resched timed wait interface
cpuidle/poll_state: Wait for need-resched via
tif_need_resched_relaxed_wait()
kunit: enable testing smp_cond_load_relaxed_timeout()
kunit: add tests for smp_cond_load_relaxed_timeout()
Documentation/atomic_t.txt | 14 +--
arch/arm64/Kconfig | 3 +
arch/arm64/include/asm/barrier.h | 23 +++++
arch/arm64/include/asm/cmpxchg.h | 62 ++++++++++---
arch/arm64/include/asm/delay-const.h | 27 ++++++
arch/arm64/include/asm/rqspinlock.h | 85 ------------------
arch/arm64/lib/delay.c | 17 ++--
drivers/clocksource/arm_arch_timer.c | 2 +
drivers/cpuidle/poll_state.c | 21 +----
drivers/soc/qcom/rpmh-rsc.c | 8 +-
include/asm-generic/barrier.h | 95 ++++++++++++++++++++
include/linux/atomic.h | 10 +++
include/linux/atomic/atomic-long.h | 18 ++--
include/linux/sched/idle.h | 29 +++++++
kernel/bpf/rqspinlock.c | 77 +++++++++++------
lib/Kconfig.debug | 10 +++
lib/tests/Makefile | 1 +
lib/tests/barrier-timeout-test.c | 125 +++++++++++++++++++++++++++
scripts/atomic/gen-atomic-long.sh | 16 ++--
19 files changed, 465 insertions(+), 178 deletions(-)
create mode 100644 arch/arm64/include/asm/delay-const.h
create mode 100644 lib/tests/barrier-timeout-test.c
--
2.31.1
^ permalink raw reply
* [PATCH v11 01/14] asm-generic: barrier: Add smp_cond_load_relaxed_timeout()
From: Ankur Arora @ 2026-04-08 12:25 UTC (permalink / raw)
To: linux-kernel, linux-arch, linux-arm-kernel, linux-pm, bpf
Cc: arnd, catalin.marinas, will, peterz, akpm, mark.rutland, harisokn,
cl, ast, rafael, daniel.lezcano, memxor, zhenglifeng1, xueshuai,
rdunlap, david.laight.linux, joao.m.martins, boris.ostrovsky,
konrad.wilk, ashok.bhat, Ankur Arora
In-Reply-To: <20260408122538.3610871-1-ankur.a.arora@oracle.com>
Add smp_cond_load_relaxed_timeout(), which extends
smp_cond_load_relaxed() to allow waiting for a duration.
We loop around waiting for the condition variable to change while
peridically doing a time-check. The loop uses cpu_poll_relax() to slow
down the busy-wait, which, unless overridden by the architecture
code, amounts to a cpu_relax().
Note that there are two ways for the time-check to fail: the timeout
case or, @time_expr_ns returning an invalid value (negative or zero).
The second failure mode allows for clocks attached to the clock-domain
of @cond_expr -- which might cease to operate meaningfully once some
state internal to @cond_expr has changed -- to fail.
Evaluation of @time_expr_ns: in the fastpath we want to keep the
performance close to smp_cond_load_relaxed(). So defer evaluation
of the potentially costly @time_expr_ns to the slowpath.
This also means that there will always be some hardware dependent
duration that has passed in cpu_poll_relax() iterations at the time
of first evaluation. Additionally cpu_poll_relax() is not guaranteed
to return at timeout boundary. In sum, expect timeout overshoot when
we exit due to expiration of the timeout.
The number of spin iterations before time-check, SMP_TIMEOUT_POLL_COUNT
is chosen to be 200 by default. With a cpu_poll_relax() iteration
taking ~20-30 cycles (measured on a variety of x86 platforms), we
expect a time-check every ~4000-6000 cycles.
The outer limit of the overshoot is double that when working with the
parameters above. This might be higher or lower depending on the
implementation of cpu_poll_relax() across architectures.
Lastly, config option ARCH_HAS_CPU_RELAX indicates availability of a
cpu_poll_relax() that is cheaper than polling. This might be relevant
for cases with a long timeout.
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-arch@vger.kernel.org
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
Notes:
- add a comment mentioning that smp_cond_load_relaxed_timeout() might
be using architectural primitives that don't support MMIO.
(David Laight, Catalin Marinas)
include/asm-generic/barrier.h | 69 +++++++++++++++++++++++++++++++++++
1 file changed, 69 insertions(+)
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index d4f581c1e21d..e5a6a1c04649 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -273,6 +273,75 @@ do { \
})
#endif
+/*
+ * Number of times we iterate in the loop before doing the time check.
+ * Note that the iteration count assumes that the loop condition is
+ * relatively cheap.
+ */
+#ifndef SMP_TIMEOUT_POLL_COUNT
+#define SMP_TIMEOUT_POLL_COUNT 200
+#endif
+
+/*
+ * Platforms with ARCH_HAS_CPU_RELAX have a cpu_poll_relax() implementation
+ * that is expected to be cheaper (lower power) than pure polling.
+ */
+#ifndef cpu_poll_relax
+#define cpu_poll_relax(ptr, val, timeout_ns) cpu_relax()
+#endif
+
+/**
+ * smp_cond_load_relaxed_timeout() - (Spin) wait for cond with no ordering
+ * guarantees until a timeout expires.
+ * @ptr: pointer to the variable to wait on.
+ * @cond_expr: boolean expression to wait for.
+ * @time_expr_ns: expression that evaluates to monotonic time (in ns) or,
+ * on failure, returns a negative value.
+ * @timeout_ns: timeout value in ns
+ * Both of the above are assumed to be compatible with s64; the signed
+ * value is used to handle the failure case in @time_expr_ns.
+ *
+ * Equivalent to using READ_ONCE() on the condition variable.
+ *
+ * Callers that expect to wait for prolonged durations might want
+ * to take into account the availability of ARCH_HAS_CPU_RELAX.
+ *
+ * Note that @ptr is expected to point to a memory address. Using this
+ * interface with MMIO will be slower (since SMP_TIMEOUT_POLL_COUNT is
+ * tuned for memory) and might also break in interesting architecture
+ * dependent ways.
+ */
+#ifndef smp_cond_load_relaxed_timeout
+#define smp_cond_load_relaxed_timeout(ptr, cond_expr, \
+ time_expr_ns, timeout_ns) \
+({ \
+ typeof(ptr) __PTR = (ptr); \
+ __unqual_scalar_typeof(*ptr) VAL; \
+ u32 __n = 0, __spin = SMP_TIMEOUT_POLL_COUNT; \
+ s64 __timeout = (s64)timeout_ns; \
+ s64 __time_now, __time_end = 0; \
+ \
+ for (;;) { \
+ VAL = READ_ONCE(*__PTR); \
+ if (cond_expr) \
+ break; \
+ cpu_poll_relax(__PTR, VAL, (u64)__timeout); \
+ if (++__n < __spin) \
+ continue; \
+ __time_now = (s64)(time_expr_ns); \
+ if (unlikely(__time_end == 0)) \
+ __time_end = __time_now + __timeout; \
+ __timeout = __time_end - __time_now; \
+ if (__time_now <= 0 || __timeout <= 0) { \
+ VAL = READ_ONCE(*__PTR); \
+ break; \
+ } \
+ __n = 0; \
+ } \
+ (typeof(*ptr))VAL; \
+})
+#endif
+
/*
* pmem_wmb() ensures that all stores for which the modification
* are written to persistent storage by preceding instructions have
--
2.31.1
^ permalink raw reply related
* [patch V2 11/11] alarmtimer: Remove unused interfaces
From: Thomas Gleixner @ 2026-04-08 11:54 UTC (permalink / raw)
To: LKML
Cc: John Stultz, Stephen Boyd, Calvin Owens, Anna-Maria Behnsen,
Frederic Weisbecker, Peter Zijlstra (Intel), Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
All alarmtimer users are converted to alarm_start_timer(). Remove the now
unused interfaces.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Stephen Boyd <sboyd@kernel.org>
---
include/linux/alarmtimer.h | 3 ---
kernel/time/alarmtimer.c | 44 --------------------------------------------
2 files changed, 47 deletions(-)
--- a/include/linux/alarmtimer.h
+++ b/include/linux/alarmtimer.h
@@ -50,9 +50,6 @@ static __always_inline ktime_t alarm_get
void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
void (*function)(struct alarm *, ktime_t));
bool alarm_start_timer(struct alarm *alarm, ktime_t expires, bool relative);
-void alarm_start(struct alarm *alarm, ktime_t start);
-void alarm_start_relative(struct alarm *alarm, ktime_t start);
-void alarm_restart(struct alarm *alarm);
int alarm_try_to_cancel(struct alarm *alarm);
int alarm_cancel(struct alarm *alarm);
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -333,39 +333,6 @@ void alarm_init(struct alarm *alarm, enu
EXPORT_SYMBOL_GPL(alarm_init);
/**
- * alarm_start - Sets an absolute alarm to fire
- * @alarm: ptr to alarm to set
- * @start: time to run the alarm
- */
-void alarm_start(struct alarm *alarm, ktime_t start)
-{
- struct alarm_base *base = &alarm_bases[alarm->type];
-
- scoped_guard(spinlock_irqsave, &base->lock) {
- alarm->node.expires = start;
- alarmtimer_enqueue(base, alarm);
- hrtimer_start(&alarm->timer, alarm->node.expires, HRTIMER_MODE_ABS);
- }
-
- trace_alarmtimer_start(alarm, base->get_ktime());
-}
-EXPORT_SYMBOL_GPL(alarm_start);
-
-/**
- * alarm_start_relative - Sets a relative alarm to fire
- * @alarm: ptr to alarm to set
- * @start: time relative to now to run the alarm
- */
-void alarm_start_relative(struct alarm *alarm, ktime_t start)
-{
- struct alarm_base *base = &alarm_bases[alarm->type];
-
- start = ktime_add_safe(start, base->get_ktime());
- alarm_start(alarm, start);
-}
-EXPORT_SYMBOL_GPL(alarm_start_relative);
-
-/**
* alarm_start_timer - Sets an alarm to fire
* @alarm: Pointer to alarm to set
* @expires: Expiry time
@@ -393,17 +360,6 @@ bool alarm_start_timer(struct alarm *ala
}
EXPORT_SYMBOL_GPL(alarm_start_timer);
-void alarm_restart(struct alarm *alarm)
-{
- struct alarm_base *base = &alarm_bases[alarm->type];
-
- guard(spinlock_irqsave)(&base->lock);
- hrtimer_set_expires(&alarm->timer, alarm->node.expires);
- hrtimer_restart(&alarm->timer);
- alarmtimer_enqueue(base, alarm);
-}
-EXPORT_SYMBOL_GPL(alarm_restart);
-
/**
* alarm_try_to_cancel - Tries to cancel an alarm timer
* @alarm: ptr to alarm to be canceled
^ permalink raw reply
* [patch V2 10/11] netfilter: xt_IDLETIMER: Switch to alarm_start_timer()
From: Thomas Gleixner @ 2026-04-08 11:54 UTC (permalink / raw)
To: LKML
Cc: Pablo Neira Ayuso, Florian Westphal, Phil Sutter, netfilter-devel,
coreteam, Calvin Owens, Anna-Maria Behnsen, Frederic Weisbecker,
Peter Zijlstra (Intel), John Stultz, Stephen Boyd, Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm
In-Reply-To: <20260408102356.783133335@kernel.org>
The existing alarm_start() interface is replaced with the new
alarm_start_timer() mechanism, which does not longer queue an already
expired timer and returns the state.
Adjust the code to utilize this so it schedules the work in the case that
the timer was already expired. Unlikely to happen as the timeout is at
least a second, but not impossible especially with virtualization.
No functional change intended
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Florian Westphal <fw@strlen.de>
Cc: Phil Sutter <phil@nwl.cc>
Cc: netfilter-devel@vger.kernel.org
Cc: coreteam@netfilter.org
---
net/netfilter/xt_IDLETIMER.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
--- a/net/netfilter/xt_IDLETIMER.c
+++ b/net/netfilter/xt_IDLETIMER.c
@@ -115,6 +115,21 @@ static void idletimer_tg_alarmproc(struc
schedule_work(&timer->work);
}
+static void idletimer_start_alarm_ktime(struct idletimer_tg *timer, ktime_t timeout)
+{
+ /*
+ * The timer should always be queued as @tout it should be least one
+ * second, but handle it correctly in any case. Virt will manage!
+ */
+ if (!alarm_start_timer(&timer->alarm, timeout, true))
+ schedule_work(&timer->work);
+}
+
+static void idletimer_start_alarm_sec(struct idletimer_tg *timer, unsigned int seconds)
+{
+ idletimer_start_alarm_ktime(timer, ktime_set(seconds, 0));
+}
+
static int idletimer_check_sysfs_name(const char *name, unsigned int size)
{
int ret;
@@ -220,12 +235,10 @@ static int idletimer_tg_create_v1(struct
INIT_WORK(&info->timer->work, idletimer_tg_work);
if (info->timer->timer_type & XT_IDLETIMER_ALARM) {
- ktime_t tout;
alarm_init(&info->timer->alarm, ALARM_BOOTTIME,
idletimer_tg_alarmproc);
info->timer->alarm.data = info->timer;
- tout = ktime_set(info->timeout, 0);
- alarm_start_relative(&info->timer->alarm, tout);
+ idletimer_start_alarm_sec(info->timer, info->timeout);
} else {
timer_setup(&info->timer->timer, idletimer_tg_expired, 0);
mod_timer(&info->timer->timer,
@@ -271,8 +284,7 @@ static unsigned int idletimer_tg_target_
info->label, info->timeout);
if (info->timer->timer_type & XT_IDLETIMER_ALARM) {
- ktime_t tout = ktime_set(info->timeout, 0);
- alarm_start_relative(&info->timer->alarm, tout);
+ idletimer_start_alarm_sec(info->timer, info->timeout);
} else {
mod_timer(&info->timer->timer,
secs_to_jiffies(info->timeout) + jiffies);
@@ -378,7 +390,7 @@ static int idletimer_tg_checkentry_v1(co
if (ktimespec.tv_sec > 0) {
pr_debug("time_expiry_remaining %lld\n",
ktimespec.tv_sec);
- alarm_start_relative(&info->timer->alarm, tout);
+ idletimer_start_alarm_ktime(info->timer, tout);
}
} else {
mod_timer(&info->timer->timer,
^ permalink raw reply
* [patch V2 09/11] power: supply: charger-manager: Switch to alarm_start_timer()
From: Thomas Gleixner @ 2026-04-08 11:54 UTC (permalink / raw)
To: LKML
Cc: Sebastian Reichel, linux-pm, Calvin Owens, Anna-Maria Behnsen,
Frederic Weisbecker, Peter Zijlstra (Intel), John Stultz,
Stephen Boyd, Alexander Viro, Christian Brauner, Jan Kara,
linux-fsdevel, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
The existing alarm_start() interface is replaced with the new
alarm_start_timer() mechanism, which does not longer queue an already
expired timer and returns the state. Adjust the code to utilize this.
No functional change intended.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: linux-pm@vger.kernel.org
---
V2: Rename to alarm_start_timer()
---
drivers/power/supply/charger-manager.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
--- a/drivers/power/supply/charger-manager.c
+++ b/drivers/power/supply/charger-manager.c
@@ -881,7 +881,7 @@ static bool cm_setup_timer(void)
mutex_unlock(&cm_list_mtx);
if (timer_req && cm_timer) {
- ktime_t now, add;
+ ktime_t exp;
/*
* Set alarm with the polling interval (wakeup_ms)
@@ -893,14 +893,16 @@ static bool cm_setup_timer(void)
pr_info("Charger Manager wakeup timer: %u ms\n", wakeup_ms);
- now = ktime_get_boottime();
- add = ktime_set(wakeup_ms / MSEC_PER_SEC,
+ exp = ktime_set(wakeup_ms / MSEC_PER_SEC,
(wakeup_ms % MSEC_PER_SEC) * NSEC_PER_MSEC);
- alarm_start(cm_timer, ktime_add(now, add));
cm_suspend_duration_ms = wakeup_ms;
- return true;
+ /*
+ * The timer should always be queued as the timeout is at least
+ * two seconds out. Handle it correctly nevertheless.
+ */
+ return alarm_start_timer(cm_timer, exp, true);
}
return false;
}
^ permalink raw reply
* [patch V2 08/11] fs/timerfd: Use the new alarm/hrtimer functions
From: Thomas Gleixner @ 2026-04-08 11:54 UTC (permalink / raw)
To: LKML
Cc: Alexander Viro, Christian Brauner, Jan Kara, Anna-Maria Behnsen,
Frederic Weisbecker, linux-fsdevel, Calvin Owens,
Peter Zijlstra (Intel), John Stultz, Stephen Boyd,
Sebastian Reichel, linux-pm, Pablo Neira Ayuso, Florian Westphal,
Phil Sutter, netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
Like any other user controlled interface, timerfd based timers can be
programmed with expiry times in the past or vary small intervals.
Both hrtimer and alarmtimer provide new interfaces which return the queued
state of the timer. If the timer was already expired, then let the callsite
handle the timerfd context update so that the full round trip through the
hrtimer interrupt is avoided.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
---
V2: Rename to alarm_timer_start() and add a comment explaining the -1 in
the tick accounting. - Peter
---
fs/timerfd.c | 117 ++++++++++++++++++++++++++++++++++-------------------------
1 file changed, 68 insertions(+), 49 deletions(-)
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -55,6 +55,15 @@ static inline bool isalarm(struct timerf
ctx->clockid == CLOCK_BOOTTIME_ALARM;
}
+static void __timerfd_triggered(struct timerfd_ctx *ctx)
+{
+ lockdep_assert_held(&ctx->wqh.lock);
+
+ ctx->expired = 1;
+ ctx->ticks++;
+ wake_up_locked_poll(&ctx->wqh, EPOLLIN);
+}
+
/*
* This gets called when the timer event triggers. We set the "expired"
* flag, but we do not re-arm the timer (in case it's necessary,
@@ -62,13 +71,8 @@ static inline bool isalarm(struct timerf
*/
static void timerfd_triggered(struct timerfd_ctx *ctx)
{
- unsigned long flags;
-
- spin_lock_irqsave(&ctx->wqh.lock, flags);
- ctx->expired = 1;
- ctx->ticks++;
- wake_up_locked_poll(&ctx->wqh, EPOLLIN);
- spin_unlock_irqrestore(&ctx->wqh.lock, flags);
+ guard(spinlock_irqsave)(&ctx->wqh.lock);
+ __timerfd_triggered(ctx);
}
static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
@@ -184,15 +188,54 @@ static ktime_t timerfd_get_remaining(str
return remaining < 0 ? 0: remaining;
}
+static void timerfd_alarm_start(struct timerfd_ctx *ctx, ktime_t exp, bool relative)
+{
+ /* Start the timer. If it's expired already, handle the callback. */
+ if (!alarm_start_timer(&ctx->t.alarm, exp, relative))
+ __timerfd_triggered(ctx);
+}
+
+static u64 timerfd_alarm_restart(struct timerfd_ctx *ctx)
+{
+ /* -1 to account for ctx->ticks++ in __timerfd_triggered() */
+ u64 ticks = alarm_forward_now(&ctx->t.alarm, ctx->tintv) - 1;
+
+ timerfd_alarm_start(ctx, alarm_get_expires(&ctx->t.alarm), false);
+ return ticks;
+}
+
+static void timerfd_hrtimer_start(struct timerfd_ctx *ctx, ktime_t exp,
+ const enum hrtimer_mode mode)
+{
+ /* Start the timer. If it's expired already, handle the callback. */
+ if (!hrtimer_start_range_ns_user(&ctx->t.tmr, exp, 0, mode))
+ __timerfd_triggered(ctx);
+}
+
+static u64 timerfd_hrtimer_restart(struct timerfd_ctx *ctx)
+{
+ /* -1 to account for ctx->ticks++ in __timerfd_triggered() */
+ u64 ticks = hrtimer_forward_now(&ctx->t.tmr, ctx->tintv) - 1;
+
+ timerfd_hrtimer_start(ctx, hrtimer_get_expires(&ctx->t.tmr), HRTIMER_MODE_ABS);
+ return ticks;
+}
+
+static u64 timerfd_restart(struct timerfd_ctx *ctx)
+{
+ if (isalarm(ctx))
+ return timerfd_alarm_restart(ctx);
+ return timerfd_hrtimer_restart(ctx);
+}
+
static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
const struct itimerspec64 *ktmr)
{
+ int clockid = ctx->clockid;
enum hrtimer_mode htmode;
ktime_t texp;
- int clockid = ctx->clockid;
- htmode = (flags & TFD_TIMER_ABSTIME) ?
- HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
+ htmode = (flags & TFD_TIMER_ABSTIME) ? HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
texp = timespec64_to_ktime(ktmr->it_value);
ctx->expired = 0;
@@ -206,20 +249,15 @@ static int timerfd_setup(struct timerfd_
timerfd_alarmproc);
} else {
hrtimer_setup(&ctx->t.tmr, timerfd_tmrproc, clockid, htmode);
- hrtimer_set_expires(&ctx->t.tmr, texp);
}
if (texp != 0) {
if (flags & TFD_TIMER_ABSTIME)
texp = timens_ktime_to_host(clockid, texp);
- if (isalarm(ctx)) {
- if (flags & TFD_TIMER_ABSTIME)
- alarm_start(&ctx->t.alarm, texp);
- else
- alarm_start_relative(&ctx->t.alarm, texp);
- } else {
- hrtimer_start(&ctx->t.tmr, texp, htmode);
- }
+ if (isalarm(ctx))
+ timerfd_alarm_start(ctx, texp, !(flags & TFD_TIMER_ABSTIME));
+ else
+ timerfd_hrtimer_start(ctx, texp, htmode);
if (timerfd_canceled(ctx))
return -ECANCELED;
@@ -287,27 +325,19 @@ static ssize_t timerfd_read_iter(struct
}
if (ctx->ticks) {
- ticks = ctx->ticks;
+ unsigned int expired = ctx->expired;
- if (ctx->expired && ctx->tintv) {
- /*
- * If tintv != 0, this is a periodic timer that
- * needs to be re-armed. We avoid doing it in the timer
- * callback to avoid DoS attacks specifying a very
- * short timer period.
- */
- if (isalarm(ctx)) {
- ticks += alarm_forward_now(
- &ctx->t.alarm, ctx->tintv) - 1;
- alarm_restart(&ctx->t.alarm);
- } else {
- ticks += hrtimer_forward_now(&ctx->t.tmr,
- ctx->tintv) - 1;
- hrtimer_restart(&ctx->t.tmr);
- }
- }
+ ticks = ctx->ticks;
ctx->expired = 0;
ctx->ticks = 0;
+
+ /*
+ * If tintv != 0, this is a periodic timer that needs to be
+ * re-armed. We avoid doing it in the timer callback to avoid
+ * DoS attacks specifying a very short timer period.
+ */
+ if (expired && ctx->tintv)
+ ticks += timerfd_restart(ctx);
}
spin_unlock_irq(&ctx->wqh.lock);
if (ticks) {
@@ -526,18 +556,7 @@ static int do_timerfd_gettime(int ufd, s
spin_lock_irq(&ctx->wqh.lock);
if (ctx->expired && ctx->tintv) {
ctx->expired = 0;
-
- if (isalarm(ctx)) {
- ctx->ticks +=
- alarm_forward_now(
- &ctx->t.alarm, ctx->tintv) - 1;
- alarm_restart(&ctx->t.alarm);
- } else {
- ctx->ticks +=
- hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
- - 1;
- hrtimer_restart(&ctx->t.tmr);
- }
+ ctx->ticks += timerfd_restart(ctx);
}
t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
t->it_interval = ktime_to_timespec64(ctx->tintv);
^ permalink raw reply
* [patch V2 07/11] alarmtimer: Convert posix timer functions to alarm_start_timer()
From: Thomas Gleixner @ 2026-04-08 11:54 UTC (permalink / raw)
To: LKML
Cc: John Stultz, Stephen Boyd, Calvin Owens, Anna-Maria Behnsen,
Frederic Weisbecker, Peter Zijlstra (Intel), Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
Use the new alarm_start_timer() for arming and rearming posix interval
timers and for clock_nanosleep() so that already expired timers do not go
through the full timer interrupt cycle.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Cc: Stephen Boyd <sboyd@kernel.org>
---
V2: Rename to alarm_start_timer()
---
kernel/time/alarmtimer.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -560,8 +560,7 @@ static bool alarm_timer_rearm(struct k_i
struct alarm *alarm = &timr->it.alarm.alarmtimer;
timr->it_overrun += alarm_forward_now(alarm, timr->it_interval);
- alarm_start(alarm, alarm->node.expires);
- return true;
+ return alarm_start_timer(alarm, alarm->node.expires, false);
}
/**
@@ -625,11 +624,16 @@ static bool alarm_timer_arm(struct k_iti
if (!absolute)
expires = ktime_add_safe(expires, base->get_ktime());
- if (sigev_none)
+
+ /*
+ * sigev_none needs to update the expires value and pretend
+ * that the timer is queued
+ */
+ if (sigev_none) {
alarm->node.expires = expires;
- else
- alarm_start(&timr->it.alarm.alarmtimer, expires);
- return true;
+ return true;
+ }
+ return alarm_start_timer(&timr->it.alarm.alarmtimer, expires, false);
}
/**
@@ -736,7 +740,9 @@ static int alarmtimer_do_nsleep(struct a
alarm->data = (void *)current;
do {
set_current_state(TASK_INTERRUPTIBLE);
- alarm_start(alarm, absexp);
+ if (!alarm_start_timer(alarm, absexp, false))
+ alarm->data = NULL;
+
if (likely(alarm->data))
schedule();
^ permalink raw reply
* [patch V2 06/11] alarmtimer: Provide alarm_start_timer()
From: Thomas Gleixner @ 2026-04-08 11:54 UTC (permalink / raw)
To: LKML
Cc: John Stultz, Stephen Boyd, Calvin Owens, Anna-Maria Behnsen,
Frederic Weisbecker, Peter Zijlstra (Intel), Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
Alarm timers utilize hrtimers for normal operation and only switch to the
RTC on suspend. In order to catch already expired timers early and without
going through a timer interrupt cycle, provide a new start function which
internally uses hrtimer_start_range_ns_user().
If hrtimer_start_range_ns_user() detects an already expired timer, it does
not queue it. In that case remove the timer from the alarm base as well.
Return the status queued or not back to the caller to handle the early
expiry.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Cc: Stephen Boyd <sboyd@kernel.org>
---
V2: Rename to alarm_start_timer() - Peter
---
include/linux/alarmtimer.h | 6 ++++++
kernel/time/alarmtimer.c | 28 ++++++++++++++++++++++++++++
2 files changed, 34 insertions(+)
--- a/include/linux/alarmtimer.h
+++ b/include/linux/alarmtimer.h
@@ -42,8 +42,14 @@ struct alarm {
void *data;
};
+static __always_inline ktime_t alarm_get_expires(struct alarm *alarm)
+{
+ return alarm->node.expires;
+}
+
void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
void (*function)(struct alarm *, ktime_t));
+bool alarm_start_timer(struct alarm *alarm, ktime_t expires, bool relative);
void alarm_start(struct alarm *alarm, ktime_t start);
void alarm_start_relative(struct alarm *alarm, ktime_t start);
void alarm_restart(struct alarm *alarm);
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -365,6 +365,34 @@ void alarm_start_relative(struct alarm *
}
EXPORT_SYMBOL_GPL(alarm_start_relative);
+/**
+ * alarm_start_timer - Sets an alarm to fire
+ * @alarm: Pointer to alarm to set
+ * @expires: Expiry time
+ * @relative: True if @expires is relative
+ *
+ * Returns: True if the alarm was queued. False if it already expired
+ */
+bool alarm_start_timer(struct alarm *alarm, ktime_t expires, bool relative)
+{
+ struct alarm_base *base = &alarm_bases[alarm->type];
+
+ if (relative)
+ expires = ktime_add_safe(expires, base->get_ktime());
+
+ trace_alarmtimer_start(alarm, base->get_ktime());
+
+ guard(spinlock_irqsave)(&base->lock);
+ alarm->node.expires = expires;
+ alarmtimer_enqueue(base, alarm);
+ if (!hrtimer_start_range_ns_user(&alarm->timer, expires, 0, HRTIMER_MODE_ABS)) {
+ alarmtimer_dequeue(base, alarm);
+ return false;
+ }
+ return true;
+}
+EXPORT_SYMBOL_GPL(alarm_start_timer);
+
void alarm_restart(struct alarm *alarm)
{
struct alarm_base *base = &alarm_bases[alarm->type];
^ permalink raw reply
* [patch V2 05/11] posix-timers: Switch to hrtimer_start_expires_user()
From: Thomas Gleixner @ 2026-04-08 11:54 UTC (permalink / raw)
To: LKML
Cc: Peter Zijlstra (Intel), Anna-Maria Behnsen, Frederic Weisbecker,
Calvin Owens, John Stultz, Stephen Boyd, Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
Switch the arm and rearm callbacks for hrtimer based posix timers over to
hrtimer_start_expires_user() so that already expired timers are not
queued. Hand the result back to the caller, which then queues the signal.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
kernel/time/posix-timers.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -293,8 +293,7 @@ static bool common_hrtimer_rearm(struct
struct hrtimer *timer = &timr->it.real.timer;
timr->it_overrun += hrtimer_forward_now(timer, timr->it_interval);
- hrtimer_restart(timer);
- return true;
+ return hrtimer_start_expires_user(timer, HRTIMER_MODE_ABS);
}
static bool __posixtimer_deliver_signal(struct kernel_siginfo *info, struct k_itimer *timr)
@@ -829,9 +828,11 @@ static bool common_hrtimer_arm(struct k_
expires = ktime_add_safe(expires, hrtimer_cb_get_time(timer));
hrtimer_set_expires(timer, expires);
- if (!sigev_none)
- hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
- return true;
+ /* For sigev_none pretend that the timer is queued */
+ if (sigev_none)
+ return true;
+
+ return hrtimer_start_expires_user(timer, HRTIMER_MODE_ABS);
}
static int common_hrtimer_try_to_cancel(struct k_itimer *timr)
^ permalink raw reply
* [patch V2 04/11] posix-timers: Handle the timer_[re]arm() return value
From: Thomas Gleixner @ 2026-04-08 11:54 UTC (permalink / raw)
To: LKML
Cc: Peter Zijlstra (Intel), Anna-Maria Behnsen, Frederic Weisbecker,
Calvin Owens, John Stultz, Stephen Boyd, Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
The [re]arm callbacks will return true when the timer was queued and false
if it was already expired at enqueue time.
In both cases the call sites can trivially queue the signal right there,
when the timer was already expired. That avoids a full round trip through
the hrtimer interrupt.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
kernel/time/posix-timers.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -299,6 +299,8 @@ static bool common_hrtimer_rearm(struct
static bool __posixtimer_deliver_signal(struct kernel_siginfo *info, struct k_itimer *timr)
{
+ bool queued;
+
guard(spinlock)(&timr->it_lock);
/*
@@ -312,12 +314,18 @@ static bool __posixtimer_deliver_signal(
if (!timr->it_interval || WARN_ON_ONCE(timr->it_status != POSIX_TIMER_REQUEUE_PENDING))
return true;
- timr->kclock->timer_rearm(timr);
- timr->it_status = POSIX_TIMER_ARMED;
+ /* timer_rearm() updates timr::it_overrun */
+ queued = timr->kclock->timer_rearm(timr);
+
timr->it_overrun_last = timr->it_overrun;
timr->it_overrun = -1LL;
++timr->it_signal_seq;
info->si_overrun = timer_overrun_to_int(timr);
+
+ if (queued)
+ timr->it_status = POSIX_TIMER_ARMED;
+ else
+ posix_timer_queue_signal(timr);
return true;
}
@@ -905,9 +913,13 @@ int common_timer_set(struct k_itimer *ti
expires = timens_ktime_to_host(timr->it_clock, expires);
sigev_none = timr->it_sigev_notify == SIGEV_NONE;
- kc->timer_arm(timr, expires, flags & TIMER_ABSTIME, sigev_none);
- if (!sigev_none)
- timr->it_status = POSIX_TIMER_ARMED;
+ if (kc->timer_arm(timr, expires, flags & TIMER_ABSTIME, sigev_none)) {
+ if (!sigev_none)
+ timr->it_status = POSIX_TIMER_ARMED;
+ } else {
+ /* Timer was already expired, queue the signal */
+ posix_timer_queue_signal(timr);
+ }
return 0;
}
^ permalink raw reply
* [patch V2 03/11] posix-timers: Expand timer_[re]arm() callbacks with a boolean return value
From: Thomas Gleixner @ 2026-04-08 11:53 UTC (permalink / raw)
To: LKML
Cc: Peter Zijlstra (Intel), John Stultz, Stephen Boyd,
Anna-Maria Behnsen, Frederic Weisbecker, Calvin Owens,
Alexander Viro, Christian Brauner, Jan Kara, linux-fsdevel,
Sebastian Reichel, linux-pm, Pablo Neira Ayuso, Florian Westphal,
Phil Sutter, netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
In order to catch expiry times which are already in the past the
timer_arm() and timer_rearm() callbacks need to be able to report back to
the caller whether the timer has been queued or not.
Change the function signature and let all implementations return true for
now. While at it simplify posix_cpu_timer_rearm().
No functional change intended.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: John Stultz <jstultz@google.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
kernel/time/alarmtimer.c | 6 ++++--
kernel/time/posix-cpu-timers.c | 18 ++++++++++--------
kernel/time/posix-timers.c | 6 ++++--
kernel/time/posix-timers.h | 4 ++--
4 files changed, 20 insertions(+), 14 deletions(-)
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -527,12 +527,13 @@ static void alarm_handle_timer(struct al
* alarm_timer_rearm - Posix timer callback for rearming timer
* @timr: Pointer to the posixtimer data struct
*/
-static void alarm_timer_rearm(struct k_itimer *timr)
+static bool alarm_timer_rearm(struct k_itimer *timr)
{
struct alarm *alarm = &timr->it.alarm.alarmtimer;
timr->it_overrun += alarm_forward_now(alarm, timr->it_interval);
alarm_start(alarm, alarm->node.expires);
+ return true;
}
/**
@@ -588,7 +589,7 @@ static void alarm_timer_wait_running(str
* @absolute: Expiry value is absolute time
* @sigev_none: Posix timer does not deliver signals
*/
-static void alarm_timer_arm(struct k_itimer *timr, ktime_t expires,
+static bool alarm_timer_arm(struct k_itimer *timr, ktime_t expires,
bool absolute, bool sigev_none)
{
struct alarm *alarm = &timr->it.alarm.alarmtimer;
@@ -600,6 +601,7 @@ static void alarm_timer_arm(struct k_iti
alarm->node.expires = expires;
else
alarm_start(&timr->it.alarm.alarmtimer, expires);
+ return true;
}
/**
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -19,7 +19,7 @@
#include "posix-timers.h"
-static void posix_cpu_timer_rearm(struct k_itimer *timer);
+static bool posix_cpu_timer_rearm(struct k_itimer *timer);
void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
{
@@ -1011,24 +1011,27 @@ static void check_process_timers(struct
/*
* This is called from the signal code (via posixtimer_rearm)
* when the last timer signal was delivered and we have to reload the timer.
+ *
+ * Return true unconditionally so the core code assumes the timer to be
+ * armed. Otherwise it would requeue the signal.
*/
-static void posix_cpu_timer_rearm(struct k_itimer *timer)
+static bool posix_cpu_timer_rearm(struct k_itimer *timer)
{
clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
- struct task_struct *p;
struct sighand_struct *sighand;
+ struct task_struct *p;
unsigned long flags;
u64 now;
- rcu_read_lock();
+ guard(rcu)();
p = cpu_timer_task_rcu(timer);
if (!p)
- goto out;
+ return true;
/* Protect timer list r/w in arm_timer() */
sighand = lock_task_sighand(p, &flags);
if (unlikely(sighand == NULL))
- goto out;
+ return true;
/*
* Fetch the current sample and update the timer's expiry time.
@@ -1045,8 +1048,7 @@ static void posix_cpu_timer_rearm(struct
*/
arm_timer(timer, p);
unlock_task_sighand(p, &flags);
-out:
- rcu_read_unlock();
+ return true;
}
/**
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -288,12 +288,13 @@ static inline int timer_overrun_to_int(s
return (int)timr->it_overrun_last;
}
-static void common_hrtimer_rearm(struct k_itimer *timr)
+static bool common_hrtimer_rearm(struct k_itimer *timr)
{
struct hrtimer *timer = &timr->it.real.timer;
timr->it_overrun += hrtimer_forward_now(timer, timr->it_interval);
hrtimer_restart(timer);
+ return true;
}
static bool __posixtimer_deliver_signal(struct kernel_siginfo *info, struct k_itimer *timr)
@@ -795,7 +796,7 @@ SYSCALL_DEFINE1(timer_getoverrun, timer_
return timer_overrun_to_int(scoped_timer);
}
-static void common_hrtimer_arm(struct k_itimer *timr, ktime_t expires,
+static bool common_hrtimer_arm(struct k_itimer *timr, ktime_t expires,
bool absolute, bool sigev_none)
{
struct hrtimer *timer = &timr->it.real.timer;
@@ -822,6 +823,7 @@ static void common_hrtimer_arm(struct k_
if (!sigev_none)
hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
+ return true;
}
static int common_hrtimer_try_to_cancel(struct k_itimer *timr)
--- a/kernel/time/posix-timers.h
+++ b/kernel/time/posix-timers.h
@@ -27,11 +27,11 @@ struct k_clock {
int (*timer_del)(struct k_itimer *timr);
void (*timer_get)(struct k_itimer *timr,
struct itimerspec64 *cur_setting);
- void (*timer_rearm)(struct k_itimer *timr);
+ bool (*timer_rearm)(struct k_itimer *timr);
s64 (*timer_forward)(struct k_itimer *timr, ktime_t now);
ktime_t (*timer_remaining)(struct k_itimer *timr, ktime_t now);
int (*timer_try_to_cancel)(struct k_itimer *timr);
- void (*timer_arm)(struct k_itimer *timr, ktime_t expires,
+ bool (*timer_arm)(struct k_itimer *timr, ktime_t expires,
bool absolute, bool sigev_none);
void (*timer_wait_running)(struct k_itimer *timr);
};
^ permalink raw reply
* [patch V2 02/11] hrtimer: Use hrtimer_start_expires_user() for hrtimer sleepers
From: Thomas Gleixner @ 2026-04-08 11:53 UTC (permalink / raw)
To: LKML
Cc: Peter Zijlstra (Intel), Anna-Maria Behnsen, Frederic Weisbecker,
Calvin Owens, John Stultz, Stephen Boyd, Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
Most hrtimer sleepers are user controlled and user space can hand arbitrary
expiry values in as long as they are valid timespecs. If the expiry value
is in the past then this requires a full loop through reprogramming the
clock event device, taking the hrtimer interrupt, waking the task and
reprogram again.
Use hrtimer_start_expires_user() which avoids the full round trip by
checking the timer for expiry on enqueue.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
kernel/time/hrtimer.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2152,7 +2152,11 @@ void hrtimer_sleeper_start_expires(struc
if (IS_ENABLED(CONFIG_PREEMPT_RT) && sl->timer.is_hard)
mode |= HRTIMER_MODE_HARD;
- hrtimer_start_expires(&sl->timer, mode);
+ /* If already expired, clear the task pointer and set current state to running */
+ if (!hrtimer_start_expires_user(&sl->timer, mode)) {
+ sl->task = NULL;
+ __set_current_state(TASK_RUNNING);
+ }
}
EXPORT_SYMBOL_GPL(hrtimer_sleeper_start_expires);
^ permalink raw reply
* [patch V2 01/11] hrtimer: Provide hrtimer_start_range_ns_user()
From: Thomas Gleixner @ 2026-04-08 11:53 UTC (permalink / raw)
To: LKML
Cc: Calvin Owens, Anna-Maria Behnsen, Frederic Weisbecker,
Peter Zijlstra (Intel), John Stultz, Stephen Boyd, Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
In-Reply-To: <20260408102356.783133335@kernel.org>
Calvin reported an odd NMI watchdog lockup which claims that the CPU locked
up in user space. He provided a reproducer, which set's up a timerfd based
timer and then rearms it in a loop with an absolute expiry time of 1ns.
As the expiry time is in the past, the timer ends up as the first expiring
timer in the per CPU hrtimer base and the clockevent device is programmed
with the minimum delta value. If the machine is fast enough, this ends up
in a endless loop of programming the delta value to the minimum value
defined by the clock event device, before the timer interrupt can fire,
which starves the interrupt and consequently triggers the lockup detector
because the hrtimer callback of the lockup mechanism is never invoked.
The clockevents code already has a last resort mechanism to prevent that,
but it's sensible to catch such issues before trying to reprogram the clock
event device.
Provide a variant of hrtimer_start_range_ns(), which sanity checks the
timer after queueing it. It does not so before because the timer might be
armed and therefore needs to be dequeued. also we optimize for the latest
possible point to check, so that the clock event prevention is avoided as
much as possible.
If the timer is already expired _before_ the clock event is reprogrammed,
remove the timer from the queue and signal to the caller that the operation
failed by returning false.
That allows the caller to take immediate action without going through the
loops and hoops of the hrtimer interrupt.
The queueing code can't invoke the timer callback as the caller might hold
a lock which is taken in the callback.
Add a tracepoint which allows to analyze the expired at start situation.
Reported-by: Calvin Owens <calvin@wbinvd.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
V2: Moved the user check into hrtimer_start_range_ns_user() and handled
the NONE case explictly. - PeterZ
Rebased on tip timers/core
---
include/linux/hrtimer.h | 20 +++++-
include/trace/events/timer.h | 13 ++++
kernel/time/hrtimer.c | 134 +++++++++++++++++++++++++++++++++++++------
3 files changed, 148 insertions(+), 19 deletions(-)
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -206,6 +206,9 @@ static inline void destroy_hrtimer_on_st
extern void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
u64 range_ns, const enum hrtimer_mode mode);
+extern bool hrtimer_start_range_ns_user(struct hrtimer *timer, ktime_t tim,
+ u64 range_ns, const enum hrtimer_mode mode);
+
/**
* hrtimer_start - (re)start an hrtimer
* @timer: the timer to be added
@@ -223,17 +226,28 @@ static inline void hrtimer_start(struct
extern int hrtimer_cancel(struct hrtimer *timer);
extern int hrtimer_try_to_cancel(struct hrtimer *timer);
-static inline void hrtimer_start_expires(struct hrtimer *timer,
- enum hrtimer_mode mode)
+static inline void hrtimer_start_expires(struct hrtimer *timer, enum hrtimer_mode mode)
{
- u64 delta;
ktime_t soft, hard;
+ u64 delta;
+
soft = hrtimer_get_softexpires(timer);
hard = hrtimer_get_expires(timer);
delta = ktime_to_ns(ktime_sub(hard, soft));
hrtimer_start_range_ns(timer, soft, delta, mode);
}
+static inline bool hrtimer_start_expires_user(struct hrtimer *timer, enum hrtimer_mode mode)
+{
+ ktime_t soft, hard;
+ u64 delta;
+
+ soft = hrtimer_get_softexpires(timer);
+ hard = hrtimer_get_expires(timer);
+ delta = ktime_to_ns(ktime_sub(hard, soft));
+ return hrtimer_start_range_ns_user(timer, soft, delta, mode);
+}
+
void hrtimer_sleeper_start_expires(struct hrtimer_sleeper *sl,
enum hrtimer_mode mode);
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -299,6 +299,19 @@ DECLARE_EVENT_CLASS(hrtimer_class,
);
/**
+ * hrtimer_start_expired - Invoked when a expired timer was started
+ * @hrtimer: pointer to struct hrtimer
+ *
+ * Preceeded by a hrtimer_start tracepoint.
+ */
+DEFINE_EVENT(hrtimer_class, hrtimer_start_expired,
+
+ TP_PROTO(struct hrtimer *hrtimer),
+
+ TP_ARGS(hrtimer)
+);
+
+/**
* hrtimer_expire_exit - called immediately after the hrtimer callback returns
* @hrtimer: pointer to struct hrtimer
*
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1352,6 +1352,12 @@ static inline bool hrtimer_keep_base(str
return hrtimer_prefer_local(is_local, is_first, is_pinned);
}
+enum {
+ HRTIMER_REPROGRAM_NONE,
+ HRTIMER_REPROGRAM,
+ HRTIMER_REPROGRAM_FORCE,
+};
+
static bool __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, u64 delta_ns,
const enum hrtimer_mode mode, struct hrtimer_clock_base *base)
{
@@ -1410,7 +1416,7 @@ static bool __hrtimer_start_range_ns(str
/* If a deferred rearm is pending skip reprogramming the device */
if (cpu_base->deferred_rearm) {
cpu_base->deferred_needs_update = true;
- return false;
+ return HRTIMER_REPROGRAM_NONE;
}
if (!was_first || cpu_base != this_cpu_base) {
@@ -1423,7 +1429,7 @@ static bool __hrtimer_start_range_ns(str
* callbacks.
*/
if (likely(hrtimer_base_is_online(this_cpu_base)))
- return first;
+ return first ? HRTIMER_REPROGRAM : HRTIMER_REPROGRAM_NONE;
/*
* Timer was enqueued remote because the current base is
@@ -1432,7 +1438,7 @@ static bool __hrtimer_start_range_ns(str
*/
if (first)
smp_call_function_single_async(cpu_base->cpu, &cpu_base->csd);
- return false;
+ return HRTIMER_REPROGRAM_NONE;
}
/*
@@ -1446,7 +1452,7 @@ static bool __hrtimer_start_range_ns(str
*/
if (timer->is_lazy) {
if (cpu_base->expires_next <= hrtimer_get_expires(timer))
- return false;
+ return HRTIMER_REPROGRAM_NONE;
}
/*
@@ -1455,8 +1461,24 @@ static bool __hrtimer_start_range_ns(str
* reprogram the hardware by evaluating the new first expiring
* timer.
*/
- hrtimer_force_reprogram(cpu_base, /* skip_equal */ true);
- return false;
+ return HRTIMER_REPROGRAM_FORCE;
+}
+
+static int hrtimer_start_range_ns_common(struct hrtimer *timer, ktime_t tim,
+ u64 delta_ns, const enum hrtimer_mode mode,
+ struct hrtimer_clock_base *base)
+{
+ /*
+ * Check whether the HRTIMER_MODE_SOFT bit and hrtimer.is_soft
+ * match on CONFIG_PREEMPT_RT = n. With PREEMPT_RT check the hard
+ * expiry mode because unmarked timers are moved to softirq expiry.
+ */
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+ WARN_ON_ONCE(!(mode & HRTIMER_MODE_SOFT) ^ !timer->is_soft);
+ else
+ WARN_ON_ONCE(!(mode & HRTIMER_MODE_HARD) ^ !timer->is_hard);
+
+ return __hrtimer_start_range_ns(timer, tim, delta_ns, mode, base);
}
/**
@@ -1476,24 +1498,104 @@ void hrtimer_start_range_ns(struct hrtim
debug_hrtimer_assert_init(timer);
+ base = lock_hrtimer_base(timer, &flags);
+
+ switch (hrtimer_start_range_ns_common(timer, tim, delta_ns, mode, base)) {
+ case HRTIMER_REPROGRAM:
+ hrtimer_reprogram(timer, true);
+ break;
+ case HRTIMER_REPROGRAM_FORCE:
+ hrtimer_force_reprogram(timer->base->cpu_base, 1);
+ break;
+ case HRTIMER_REPROGRAM_NONE:
+ break;
+ }
+
+ unlock_hrtimer_base(timer, &flags);
+}
+EXPORT_SYMBOL_GPL(hrtimer_start_range_ns);
+
+static inline bool hrtimer_check_user_timer(struct hrtimer *timer)
+{
+ struct hrtimer_cpu_base *cpu_base = timer->base->cpu_base;
+ ktime_t expires;
+
/*
- * Check whether the HRTIMER_MODE_SOFT bit and hrtimer.is_soft
- * match on CONFIG_PREEMPT_RT = n. With PREEMPT_RT check the hard
- * expiry mode because unmarked timers are moved to softirq expiry.
+ * This uses soft expires because that's the user provided
+ * expiry time, while expires can be further in the past
+ * due to a slack value added to the user expiry time.
*/
- if (!IS_ENABLED(CONFIG_PREEMPT_RT))
- WARN_ON_ONCE(!(mode & HRTIMER_MODE_SOFT) ^ !timer->is_soft);
- else
- WARN_ON_ONCE(!(mode & HRTIMER_MODE_HARD) ^ !timer->is_hard);
+ expires = hrtimer_get_softexpires(timer);
+
+ /* Convert to monotonic */
+ expires = ktime_sub(expires, timer->base->offset);
+
+ /*
+ * Check whether this timer will end up as the first expiring timer in
+ * the CPU base. If not, no further checks required as it's then
+ * guaranteed to expire in the future.
+ */
+ if (expires >= cpu_base->expires_next)
+ return true;
+
+ /* Validate that the expiry time is in the future. */
+ if (expires > ktime_get())
+ return true;
+
+ debug_hrtimer_deactivate(timer);
+ __remove_hrtimer(timer, timer->base, HRTIMER_STATE_INACTIVE, false);
+ trace_hrtimer_start_expired(timer);
+ return false;
+}
+
+/**
+ * hrtimer_start_range_ns_user - (re)start an user controlled hrtimer
+ * @timer: the timer to be added
+ * @tim: expiry time
+ * @delta_ns: "slack" range for the timer
+ * @mode: timer mode: absolute (HRTIMER_MODE_ABS) or
+ * relative (HRTIMER_MODE_REL), and pinned (HRTIMER_MODE_PINNED);
+ * softirq based mode is considered for debug purpose only!
+ *
+ * Returns: True when the timer was queued, false if it was already expired
+ *
+ * This function cannot invoke the timer callback for expired timers as it might
+ * be called under a lock which the timer callback needs to acquire. So the
+ * caller has to handle that case.
+ */
+bool hrtimer_start_range_ns_user(struct hrtimer *timer, ktime_t tim,
+ u64 delta_ns, const enum hrtimer_mode mode)
+{
+ struct hrtimer_clock_base *base;
+ unsigned long flags;
+ bool ret = true;
+
+ debug_hrtimer_assert_init(timer);
base = lock_hrtimer_base(timer, &flags);
- if (__hrtimer_start_range_ns(timer, tim, delta_ns, mode, base))
- hrtimer_reprogram(timer, true);
+ switch (hrtimer_start_range_ns_common(timer, tim, delta_ns, mode, base)) {
+ case HRTIMER_REPROGRAM:
+ ret = hrtimer_check_user_timer(timer);
+ if (ret)
+ hrtimer_reprogram(timer, true);
+ break;
+ case HRTIMER_REPROGRAM_FORCE:
+ ret = hrtimer_check_user_timer(timer);
+ /*
+ * The base must always be reevaluated, independent of the
+ * result above because the timer was the first pending timer.
+ */
+ hrtimer_force_reprogram(timer->base->cpu_base, 1);
+ break;
+ case HRTIMER_REPROGRAM_NONE:
+ break;
+ }
unlock_hrtimer_base(timer, &flags);
+ return ret;
}
-EXPORT_SYMBOL_GPL(hrtimer_start_range_ns);
+EXPORT_SYMBOL_GPL(hrtimer_start_range_ns_user);
/**
* hrtimer_try_to_cancel - try to deactivate a timer
^ permalink raw reply
* [patch V2 00/11] hrtimers: Prevent hrtimer interrupt starvation
From: Thomas Gleixner @ 2026-04-08 11:53 UTC (permalink / raw)
To: LKML
Cc: Calvin Owens, Anna-Maria Behnsen, Frederic Weisbecker,
Peter Zijlstra (Intel), John Stultz, Stephen Boyd, Alexander Viro,
Christian Brauner, Jan Kara, linux-fsdevel, Sebastian Reichel,
linux-pm, Pablo Neira Ayuso, Florian Westphal, Phil Sutter,
netfilter-devel, coreteam
This is a follow up to V1 which can be found here:
https://lore.kernel.org/lkml/20260407083219.478203185@kernel.org
Calvin reported an odd NMI watchdog lockup which claims that the CPU locked
up in user space:
https://lore.kernel.org/lkml/acMe-QZUel-bBYUh@mozart.vkv.me/
He provided a reproducer, which sets up a timerfd based timer and then
rearms it in a loop with an absolute expiry time of 1ns.
As the expiry time is in the past, the timer ends up as the first expiring
timer in the per CPU hrtimer base and the clockevent device is programmed
with the minimum delta value. If the machine is fast enough, this ends up
in a endless loop of programming the delta value to the minimum value
defined by the clock event device, before the timer interrupt can fire,
which starves the interrupt and consequently triggers the lockup detector
because the hrtimer callback of the lockup mechanism is never invoked.
The first patch in the V1 series changes the clockevent set next event
mechanism to prevent reprogramming of the clockevent device when the
minimum delta value was programmed unless the new delta is larger than
that. It's a less convoluted variant of the patch which was posted in the
above linked thread and was confirmed to prevent the starvation problem.
But that's only to be considered the last resort because it results in an
insane amount of avoidable hrtimer interrupts. That patch has been merged
into the tip tree already.
The problem of user controlled timers is that the input value is only
sanity checked vs. validity of the provided timespec and clamped to be in
the maximum allowable range. But for performance reasons for in kernel
usage there is no check whether a to be armed timer might have been expired
already at enqueue time.
This series addresses this by providing a separate interface to arm user
controlled timers. This works the same way as the existing
hrtimer_start_range_ns(), but in case that the timer ends up as the first
timer in the clock base after enqueue it provides additional checks:
- Whether the timer becomes the first expiring timer in the CPU base.
If not the timer is considered to expire in the future as there is
already an earlier event programmed.
- Whether the timer has expired already by comparing the expiry value
against current time.
If it is expired, the timer is removed from the clock base and the
function returns false, so that the caller can handle it. That's
required because the function cannot invoke the callback as that
might need to acquire a lock which is held by the caller.
This function is then used for the user controlled timer arming interfaces
mainly by converting hrtimer sleeper over to it. That affects a few in
kernel users too, but the overhead is minimal in that case and it spares a
tedious whack the mole game all over the tree.
The other usage sites in posixtimers, alarmtimers and timerfd are converted
as well, which should cover the vast majority of user space controllable
timers as far as my investigation goes.
Changes vs. V1:
- Dropped the clockevents patch as it is already merged
- Rebased on tip timers/core
- Moved the user check into hrtimer_start_range_ns_user() - Peter
- Renamed alarmtimer_start() to alarm_start_timer() - Peter
- Picked up tags as appropriate
The series applies against tip timers/core and is also available from git:
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git hrtimer-exp-v2
Thanks,
tglx
---
drivers/power/supply/charger-manager.c | 12 +-
fs/timerfd.c | 117 ++++++++++++++++-----------
include/linux/alarmtimer.h | 9 +-
include/linux/hrtimer.h | 20 ++++
include/trace/events/timer.h | 13 +++
kernel/time/alarmtimer.c | 70 +++++++---------
kernel/time/hrtimer.c | 140 ++++++++++++++++++++++++++++-----
kernel/time/posix-cpu-timers.c | 18 ++--
kernel/time/posix-timers.c | 35 +++++---
kernel/time/posix-timers.h | 4
net/netfilter/xt_IDLETIMER.c | 24 ++++-
11 files changed, 320 insertions(+), 142 deletions(-)
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