[PATCH v5 00/18] Refcounted interrupt disable and SpinLockIrq for Rust

[PATCH v5 00/18] Refcounted interrupt disable and SpinLockIrq for Rust

[Boqun Feng]

Hi Peter & Ingo,

Please take a look at this updated series for SpinLockIrq.

Changes since v4:

* Addressed SoB issues spotted by Peter.
* Added underflow/overflow checking for interrupt disabling counter as
  suggested by Shrikanth.
* Added a max nesting level per suggestion from Shrikanth.
* Document/comment updates.

v4: https://lore.kernel.org/lkml/20260804161447.84806-1-boqun@kernel.org/

Regards,
Boqun

Boqun Feng (10):
  preempt: Introduce HARDIRQ_DISABLE_BITS
  preempt: Introduce __preempt_count_{sub,add}_return()
  irq & spin_lock: Add counted interrupt disabling/enabling
  irq: Add max local_interrupt_disable() nesting level kunit test case
  locking: Switch to _irq_{disable,enable}() variants in cleanup guards
  sched: Remove the unused preempt_offset parameter of __cant_sleep()
  sched: Avoid signed comparison of preempt_count() in __cant_migrate()
  preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS
  arm64: sched/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS
  rust: helper: Add spin_{un,}lock_irq_{enable,disable}() helpers

Heiko Carstens (1):
  s390/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS

Joel Fernandes (1):
  preempt: Track NMI nesting to separate per-CPU counter

Lyude Paul (6):
  openrisc: Include <linux/cpumask.h> in smp.h
  irq: Add KUnit test for refcounted interrupt enable/disable
  rust: Introduce interrupt module
  rust: sync: Use super::* in spinlock.rs
  rust: sync: Add SpinLockIrq
  rust: sync: Introduce SpinLockIrq::lock_with() and friends

 arch/arm64/Kconfig                            |   1 +
 arch/arm64/include/asm/preempt.h              |  20 ++
 arch/openrisc/include/asm/smp.h               |   2 +
 arch/s390/Kconfig                             |   1 +
 arch/s390/include/asm/lowcore.h               |  13 +-
 arch/s390/include/asm/preempt.h               |  51 +--
 arch/x86/Kconfig                              |   1 +
 arch/x86/include/asm/preempt.h                |  61 +++-
 arch/x86/kernel/cpu/common.c                  |   2 +-
 include/asm-generic/preempt.h                 |  14 +
 include/linux/hardirq.h                       |  40 ++-
 include/linux/interrupt_rc.h                  |  95 +++++
 include/linux/kernel.h                        |   4 +-
 include/linux/preempt.h                       |  44 ++-
 include/linux/spinlock.h                      |  49 ++-
 include/linux/spinlock_api_smp.h              |  41 +++
 include/linux/spinlock_api_up.h               |  15 +
 include/linux/spinlock_rt.h                   |  18 +
 kernel/Kconfig.preempt                        |   4 +
 kernel/irq/Makefile                           |   1 +
 kernel/irq/refcount_interrupt_test.c          | 131 +++++++
 kernel/locking/spinlock.c                     |  31 ++
 kernel/sched/core.c                           |  18 +-
 kernel/sched/fair.c                           |  12 +-
 kernel/softirq.c                              |  36 +-
 rust/helpers/helpers.c                        |   1 +
 rust/helpers/interrupt.c                      |  18 +
 rust/helpers/spinlock.c                       |  15 +
 rust/helpers/sync.c                           |   5 +
 rust/kernel/interrupt.rs                      |  89 +++++
 rust/kernel/lib.rs                            |   1 +
 rust/kernel/sync.rs                           |   9 +-
 rust/kernel/sync/lock/global.rs               |   3 +
 rust/kernel/sync/lock/spinlock.rs             | 329 +++++++++++++++++-
 .../testing/selftests/bpf/bpf_experimental.h  |   7 +-
 35 files changed, 1092 insertions(+), 90 deletions(-)
 create mode 100644 include/linux/interrupt_rc.h
 create mode 100644 kernel/irq/refcount_interrupt_test.c
 create mode 100644 rust/helpers/interrupt.c
 create mode 100644 rust/kernel/interrupt.rs

-- 
2.50.1 (Apple Git-155)

[PATCH v5 01/18] preempt: Track NMI nesting to separate per-CPU counter

[Boqun Feng]

From: Joel Fernandes <joelagnelf@nvidia.com>

Move NMI nesting tracking from the preempt_count bits to a separate
per-CPU counter (nmi_nesting). This is to free up the NMI bits in the
preempt_count, allowing those bits to be repurposed for other uses.

Reduce NMI_BITS from 4 to 1, using it only to detect if we're in an NMI.
The per-CPU counter currently caps nesting at 15.

[boqun: Address Steven Rostedt's comment on the BUG_ON() condition]
[boqun: Use preempt_count_set() in __nmi_exit() to avoid underflow]

Suggested-by: Boqun Feng <boqun@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 include/linux/hardirq.h                        | 17 +++++++++++++----
 include/linux/preempt.h                        |  9 +++++++--
 kernel/softirq.c                               |  2 ++
 tools/testing/selftests/bpf/bpf_experimental.h |  2 +-
 4 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index d57cab4d4c06..8d4895531a45 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -10,6 +10,8 @@
 #include <linux/vtime.h>
 #include <asm/hardirq.h>
 
+DECLARE_PER_CPU(unsigned int, nmi_nesting);
+
 extern void synchronize_irq(unsigned int irq);
 extern bool synchronize_hardirq(unsigned int irq);
 
@@ -102,14 +104,17 @@ void irq_exit_rcu(void);
  */
 
 /*
- * nmi_enter() can nest up to 15 times; see NMI_BITS.
+ * nmi_enter() can nest - nesting is tracked in a per-CPU counter.
  */
 #define __nmi_enter()						\
 	do {							\
 		lockdep_off();					\
 		arch_nmi_enter();				\
-		BUG_ON(in_nmi() == NMI_MASK);			\
-		__preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET);	\
+		/* Maximum NMI nesting is 15. */		\
+		BUG_ON(__this_cpu_read(nmi_nesting) >= 15);	\
+		__this_cpu_inc(nmi_nesting);			\
+		__preempt_count_add(HARDIRQ_OFFSET);		\
+		preempt_count_set(preempt_count() | NMI_MASK);	\
 	} while (0)
 
 #define nmi_enter()						\
@@ -124,8 +129,12 @@ void irq_exit_rcu(void);
 
 #define __nmi_exit()						\
 	do {							\
+		unsigned int nesting;				\
 		BUG_ON(!in_nmi());				\
-		__preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET);	\
+		__preempt_count_sub(HARDIRQ_OFFSET);		\
+		nesting = __this_cpu_dec_return(nmi_nesting);	\
+		if (!nesting)					\
+			preempt_count_set(preempt_count() & ~NMI_MASK);	\
 		arch_nmi_exit();				\
 		lockdep_on();					\
 	} while (0)
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index d964f965c8ff..586f96688325 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -17,6 +17,8 @@
  *
  * - bits 0-7 are the preemption count (max preemption depth: 256)
  * - bits 8-15 are the softirq count (max # of softirqs: 256)
+ * - bits 16-19 are the hardirq count (max # of hardirqs: 16)
+ * - bit 20 is the NMI flag (no nesting count, tracked separately)
  *
  * The hardirq count could in theory be the same as the number of
  * interrupts in the system, but we run all interrupt handlers with
@@ -24,16 +26,19 @@
  * there are a few palaeontologic drivers which reenable interrupts in
  * the handler, so we need more than one bit here.
  *
+ * NMI nesting depth is tracked in a separate per-CPU variable
+ * (nmi_nesting) to save bits in preempt_count.
+ *
  *         PREEMPT_MASK:	0x000000ff
  *         SOFTIRQ_MASK:	0x0000ff00
  *         HARDIRQ_MASK:	0x000f0000
- *             NMI_MASK:	0x00f00000
+ *             NMI_MASK:	0x00100000
  * PREEMPT_NEED_RESCHED:	0x80000000
  */
 #define PREEMPT_BITS	8
 #define SOFTIRQ_BITS	8
 #define HARDIRQ_BITS	4
-#define NMI_BITS	4
+#define NMI_BITS	1
 
 #define PREEMPT_SHIFT	0
 #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 4425d8dce44b..10af5ed859e7 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -88,6 +88,8 @@ EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabled);
 EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
 #endif
 
+DEFINE_PER_CPU(unsigned int, nmi_nesting);
+
 /*
  * SOFTIRQ_OFFSET usage:
  *
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 67ff7882299e..e4e12001fce9 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -367,7 +367,7 @@ extern int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str,
 #define PREEMPT_BITS	8
 #define SOFTIRQ_BITS	8
 #define HARDIRQ_BITS	4
-#define NMI_BITS	4
+#define NMI_BITS	1
 
 #define PREEMPT_SHIFT	0
 #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
-- 
2.50.1 (Apple Git-155)

[PATCH v5 02/18] preempt: Introduce HARDIRQ_DISABLE_BITS

[Boqun Feng]

In order to support preempt_disable()-like interrupt disabling, that is,
using part of preempt_count() to track interrupt disabling nesting
level, change the preempt_count() layout to contain 8-bit
HARDIRQ_DISABLE count.

Co-developed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 include/linux/preempt.h                        | 16 +++++++++++-----
 tools/testing/selftests/bpf/bpf_experimental.h |  5 ++++-
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 586f96688325..e2d3079d3f5f 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -17,8 +17,9 @@
  *
  * - bits 0-7 are the preemption count (max preemption depth: 256)
  * - bits 8-15 are the softirq count (max # of softirqs: 256)
- * - bits 16-19 are the hardirq count (max # of hardirqs: 16)
- * - bit 20 is the NMI flag (no nesting count, tracked separately)
+ * - bits 16-23 are the hardirq disable count (max # of hardirq disable: 256)
+ * - bits 24-27 are the hardirq count (max # of hardirqs: 16)
+ * - bit 28 is the NMI flag (no nesting count, tracked separately)
  *
  * The hardirq count could in theory be the same as the number of
  * interrupts in the system, but we run all interrupt handlers with
@@ -31,29 +32,34 @@
  *
  *         PREEMPT_MASK:	0x000000ff
  *         SOFTIRQ_MASK:	0x0000ff00
- *         HARDIRQ_MASK:	0x000f0000
- *             NMI_MASK:	0x00100000
+ * HARDIRQ_DISABLE_MASK:	0x00ff0000
+ *         HARDIRQ_MASK:	0x0f000000
+ *             NMI_MASK:	0x10000000
  * PREEMPT_NEED_RESCHED:	0x80000000
  */
 #define PREEMPT_BITS	8
 #define SOFTIRQ_BITS	8
+#define HARDIRQ_DISABLE_BITS	8
 #define HARDIRQ_BITS	4
 #define NMI_BITS	1
 
 #define PREEMPT_SHIFT	0
 #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
-#define HARDIRQ_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
+#define HARDIRQ_DISABLE_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
+#define HARDIRQ_SHIFT	(HARDIRQ_DISABLE_SHIFT + HARDIRQ_DISABLE_BITS)
 #define NMI_SHIFT	(HARDIRQ_SHIFT + HARDIRQ_BITS)
 
 #define __IRQ_MASK(x)	((1UL << (x))-1)
 
 #define PREEMPT_MASK	(__IRQ_MASK(PREEMPT_BITS) << PREEMPT_SHIFT)
 #define SOFTIRQ_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
+#define HARDIRQ_DISABLE_MASK	(__IRQ_MASK(HARDIRQ_DISABLE_BITS) << HARDIRQ_DISABLE_SHIFT)
 #define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
 #define NMI_MASK	(__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)
 
 #define PREEMPT_OFFSET	(1UL << PREEMPT_SHIFT)
 #define SOFTIRQ_OFFSET	(1UL << SOFTIRQ_SHIFT)
+#define HARDIRQ_DISABLE_OFFSET	(1UL << HARDIRQ_DISABLE_SHIFT)
 #define HARDIRQ_OFFSET	(1UL << HARDIRQ_SHIFT)
 #define NMI_OFFSET	(1UL << NMI_SHIFT)
 
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index e4e12001fce9..0159a3d365c8 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -366,17 +366,20 @@ extern int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str,
 
 #define PREEMPT_BITS	8
 #define SOFTIRQ_BITS	8
+#define HARDIRQ_DISABLE_BITS	8
 #define HARDIRQ_BITS	4
 #define NMI_BITS	1
 
 #define PREEMPT_SHIFT	0
 #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
-#define HARDIRQ_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
+#define HARDIRQ_DISABLE_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
+#define HARDIRQ_SHIFT	(HARDIRQ_DISABLE_SHIFT + HARDIRQ_DISABLE_BITS)
 #define NMI_SHIFT	(HARDIRQ_SHIFT + HARDIRQ_BITS)
 
 #define __IRQ_MASK(x)	((1UL << (x))-1)
 
 #define SOFTIRQ_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
+#define HARDIRQ_DISABLE_MASK	(__IRQ_MASK(HARDIRQ_DISABLE_BITS) << HARDIRQ_DISABLE_SHIFT)
 #define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
 #define NMI_MASK	(__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)
 
-- 
2.50.1 (Apple Git-155)

[PATCH v5 03/18] preempt: Introduce __preempt_count_{sub,add}_return()

[Boqun Feng]

In order to use preempt_count() to track the interrupt disable nesting
level, __preempt_count_{add,sub}_return() are introduced, as their names
suggest, these primitives return the new value of the preempt_count()
after changing it. The following example shows the usage of it in
local_interrupt_disable():

	// increase the HARDIRQ_DISABLE bit
	new_count = __preempt_count_add_return(HARDIRQ_DISABLE_OFFSET);

	// if it's the first-time increment, then disable the interrupt
	// at hardware level.
	if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET) {
		local_irq_save(flags);
		raw_cpu_write(local_interrupt_disable_state, flags);
	}

Having these primitives will avoid a read of preempt_count() after
changing preempt_count() on certain architectures.

Acked-by: Heiko Carstens <hca@linux.ibm.com> # s390
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 arch/arm64/include/asm/preempt.h | 20 ++++++++++++++++++++
 arch/s390/include/asm/preempt.h  | 10 ++++++++++
 arch/x86/include/asm/preempt.h   | 10 ++++++++++
 include/asm-generic/preempt.h    | 14 ++++++++++++++
 4 files changed, 54 insertions(+)

diff --git a/arch/arm64/include/asm/preempt.h b/arch/arm64/include/asm/preempt.h
index 932ea4b62042..9ecc2766a9f2 100644
--- a/arch/arm64/include/asm/preempt.h
+++ b/arch/arm64/include/asm/preempt.h
@@ -55,6 +55,26 @@ static inline void __preempt_count_sub(int val)
 	WRITE_ONCE(current_thread_info()->preempt.count, pc);
 }
 
+static inline int __preempt_count_add_return(int val)
+{
+	u32 pc = READ_ONCE(current_thread_info()->preempt.count);
+
+	pc += val;
+	WRITE_ONCE(current_thread_info()->preempt.count, pc);
+
+	return pc;
+}
+
+static inline int __preempt_count_sub_return(int val)
+{
+	u32 pc = READ_ONCE(current_thread_info()->preempt.count);
+
+	pc -= val;
+	WRITE_ONCE(current_thread_info()->preempt.count, pc);
+
+	return pc;
+}
+
 static inline bool __preempt_count_dec_and_test(void)
 {
 	struct thread_info *ti = current_thread_info();
diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h
index 6e5821bb047e..0a25d4648b4c 100644
--- a/arch/s390/include/asm/preempt.h
+++ b/arch/s390/include/asm/preempt.h
@@ -139,6 +139,16 @@ static __always_inline bool should_resched(int preempt_offset)
 	return unlikely(READ_ONCE(get_lowcore()->preempt_count) == preempt_offset);
 }
 
+static __always_inline int __preempt_count_add_return(int val)
+{
+	return val + __atomic_add(val, &get_lowcore()->preempt_count);
+}
+
+static __always_inline int __preempt_count_sub_return(int val)
+{
+	return __preempt_count_add_return(-val);
+}
+
 #define init_task_preempt_count(p)	do { } while (0)
 /* Deferred to CPU bringup time */
 #define init_idle_preempt_count(p, cpu)	do { } while (0)
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index 578441db09f0..1220656f3370 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -85,6 +85,16 @@ static __always_inline void __preempt_count_sub(int val)
 	raw_cpu_add_4(__preempt_count, -val);
 }
 
+static __always_inline int __preempt_count_add_return(int val)
+{
+	return raw_cpu_add_return_4(__preempt_count, val);
+}
+
+static __always_inline int __preempt_count_sub_return(int val)
+{
+	return raw_cpu_add_return_4(__preempt_count, -val);
+}
+
 /*
  * Because we keep PREEMPT_NEED_RESCHED set when we do _not_ need to reschedule
  * a decrement which hits zero means we have no preempt_count and should
diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index 51f8f3881523..c8683c046615 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -59,6 +59,20 @@ static __always_inline void __preempt_count_sub(int val)
 	*preempt_count_ptr() -= val;
 }
 
+static __always_inline int __preempt_count_add_return(int val)
+{
+	*preempt_count_ptr() += val;
+
+	return *preempt_count_ptr();
+}
+
+static __always_inline int __preempt_count_sub_return(int val)
+{
+	*preempt_count_ptr() -= val;
+
+	return *preempt_count_ptr();
+}
+
 static __always_inline bool __preempt_count_dec_and_test(void)
 {
 	/*
-- 
2.50.1 (Apple Git-155)

[PATCH v5 04/18] openrisc: Include <linux/cpumask.h> in smp.h

[Boqun Feng]

From: Lyude Paul <lyude@redhat.com>

While OpenRISC currently doesn't fail to build upstream, it appears that
including <asm/smp.h> in the right headers is enough to break that -
primarily because OpenRISC's asm/smp.h header doesn't actually provide
any definition for struct cpumask. Which means the only reason we aren't
failing to build the kernel is because we've been lucky enough that
every spot including asm/smp.h already has definitions for struct
cpumask pulled in.

This became evident when trying to work on a patch series for adding
ref-counted interrupt enable/disable to the kernel, where introducing a
new interrupt_rc.h header suddenly introduced a build error on OpenRISC:

     In file included from include/linux/interrupt_rc.h:17,
                      from include/linux/spinlock.h:60,
                      from include/linux/mmzone.h:8,
                      from include/linux/gfp.h:7,
                      from include/linux/mm.h:7,
                      from arch/openrisc/include/asm/pgalloc.h:20,
                      from arch/openrisc/include/asm/io.h:18,
                      from include/linux/io.h:12,
                      from drivers/irqchip/irq-ompic.c:61:
     arch/openrisc/include/asm/smp.h:21:59: warning: 'struct cpumask'
     declared inside parameter list will not be visible outside of this
     definition or declaration
        21 | extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);
           |                                                           ^~~~~~~
     arch/openrisc/include/asm/smp.h:23:54: warning: 'struct cpumask'
     declared inside parameter list will not be visible outside of this
     definition or declaration
        23 | extern void set_smp_cross_call(void (*)(const struct cpumask *, unsigned int));
           |                                                      ^~~~~~~
     drivers/irqchip/irq-ompic.c: In function 'ompic_of_init':
  >> drivers/irqchip/irq-ompic.c:191:28: error: passing argument 1 of
     'set_smp_cross_call' from incompatible pointer type
     [-Werror=incompatible-pointer-types]
       191 |         set_smp_cross_call(ompic_raise_softirq);
           |                            ^~~~~~~~~~~~~~~~~~~
           |                            |
           |                            void (*)(const struct cpumask *, unsigned int)
     arch/openrisc/include/asm/smp.h:23:32: note: expected 'void (*)(const
     struct cpumask *, unsigned int)' but argument is of type 'void
     (*)(const struct cpumask *, unsigned int)'
        23 | extern void set_smp_cross_call(void (*)(const struct cpumask *, unsigned int));

To fix this, let's take an example from the smp.h headers of other
architectures (x86, hexagon, arm64, probably more): just include
linux/cpumask.h at the top.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Acked-by: Stafford Horne <shorne@gmail.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 arch/openrisc/include/asm/smp.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/openrisc/include/asm/smp.h b/arch/openrisc/include/asm/smp.h
index 007296f160ef..84653aaffa96 100644
--- a/arch/openrisc/include/asm/smp.h
+++ b/arch/openrisc/include/asm/smp.h
@@ -9,6 +9,8 @@
 #ifndef __ASM_OPENRISC_SMP_H
 #define __ASM_OPENRISC_SMP_H
 
+#include <linux/cpumask.h>
+
 #include <asm/spr.h>
 #include <asm/spr_defs.h>
 
-- 
2.50.1 (Apple Git-155)

[PATCH v5 05/18] irq & spin_lock: Add counted interrupt disabling/enabling

[Boqun Feng]

Currently the nested interrupt disabling and enabling is represented by
_irqsave() and _irqrestore() APIs, which are relatively unsafe, for
example:

	<interrupts are enabled as beginning>
	spin_lock_irqsave(l1, flag1);
	spin_lock_irqsave(l2, flag2);
	spin_unlock_irqrestore(l1, flags1);
	<l2 is still held but interrupts are enabled>
	// accesses to interrupt-disable protected data will cause races

This is even easier to trigger with guard facilities:

	unsigned long flag2;

	scoped_guard(spin_lock_irqsave, l1) {
		spin_lock_irqsave(l2, flag2);
	}
	// l2 locked but interrupts are enabled.
	spin_unlock_irqrestore(l2, flag2);

(Hand-to-hand locking critical sections are not uncommon for a
fine-grained lock design)

And because of this unsafety, Rust cannot easily wrap the
interrupt-disabling locks in a safe API, which complicates the design.

To resolve this, introduce a new set of interrupt disabling APIs:

*	local_interrupt_disable();
*	local_interrupt_enable();

They work like local_irq_save() and local_irq_restore() except that 1)
the outermost local_interrupt_disable() call saves the interrupt state
into a per-CPU variable, so that the outermost local_interrupt_enable()
can restore the state, and 2) a per-CPU counter is added to record the
nest level of these calls, so that interrupts are not accidentally
enabled inside the outermost critical section.

Also add the corresponding spin_lock primitives: spin_lock_irq_disable()
and spin_unlock_irq_enable(), as a result, code as follows:

	spin_lock_irq_disable(l1);
	spin_lock_irq_disable(l2);
	spin_unlock_irq_enable(l1);
	// Interrupts are still disabled.
	spin_unlock_irq_enable(l2);

doesn't have the issue that interrupts are accidentally enabled.

This also makes the wrapper of interrupt-disabling locks on Rust easier
to design.

Co-developed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
[boqun: Apply Peter's feedback and fix spell errors reported by Ingo]
[boqun: Address the duplicate spin_acquire() spotted by sashiko]
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 include/linux/interrupt_rc.h     | 95 ++++++++++++++++++++++++++++++++
 include/linux/preempt.h          |  4 ++
 include/linux/spinlock.h         | 23 ++++++++
 include/linux/spinlock_api_smp.h | 41 ++++++++++++++
 include/linux/spinlock_api_up.h  | 15 +++++
 include/linux/spinlock_rt.h      | 18 ++++++
 kernel/locking/spinlock.c        | 31 +++++++++++
 kernel/softirq.c                 | 28 +++++++++-
 8 files changed, 253 insertions(+), 2 deletions(-)
 create mode 100644 include/linux/interrupt_rc.h

diff --git a/include/linux/interrupt_rc.h b/include/linux/interrupt_rc.h
new file mode 100644
index 000000000000..bb62979270a6
--- /dev/null
+++ b/include/linux/interrupt_rc.h
@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_INTERRUPT_RC_H
+#define __LINUX_INTERRUPT_RC_H
+
+/*
+ * include/linux/interrupt_rc.h - refcounted local processor interrupt
+ * management.
+ *
+ * Since the implementation of this API currently depends on
+ * local_irq_save()/local_irq_restore(), we split this into its own header to
+ * make it easier to include without hitting circular header dependencies.
+ */
+
+#include <linux/irqflags.h>
+#include <linux/debug_locks.h>
+#include <linux/preempt.h>
+#include <linux/processor.h>
+#include <linux/smp.h>
+
+#ifndef MODULE
+/* Per-CPU interrupt disabling state for local_interrupt_{disable,enable}(). */
+DECLARE_PER_CPU(unsigned long, local_interrupt_disable_state);
+
+static __always_inline void __local_interrupt_disable(void)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	raw_cpu_write(local_interrupt_disable_state, flags);
+}
+
+static __always_inline void __local_interrupt_enable(void)
+{
+	unsigned long flags = raw_cpu_read(local_interrupt_disable_state);
+
+	local_irq_restore(flags);
+}
+
+#ifndef INSTANTIATE_EXPORTED_INTERRUPT_DISABLE
+static __always_inline void _local_interrupt_disable(void)
+{
+	__local_interrupt_disable();
+}
+
+static __always_inline void _local_interrupt_enable(void)
+{
+	__local_interrupt_enable();
+}
+#else
+extern void _local_interrupt_disable(void);
+extern void _local_interrupt_enable(void);
+#endif
+
+#else /* !MODULE */
+extern void _local_interrupt_disable(void);
+extern void _local_interrupt_enable(void);
+#endif /* !MODULE */
+
+static inline void local_interrupt_disable(void)
+{
+	int new_count;
+
+	WARN_ON_ONCE(in_nmi());
+
+	new_count = hardirq_disable_enter();
+
+	/* Is hardirq disable count overflow soon? */
+	if (IS_ENABLED(CONFIG_DEBUG_PREEMPT) &&
+	    DEBUG_LOCKS_WARN_ON((new_count & HARDIRQ_DISABLE_MASK) +
+				(10 << HARDIRQ_DISABLE_SHIFT) >=
+				HARDIRQ_DISABLE_MASK))
+	    return;
+
+	/* Interrupts can happen here, but it's OK, see __irq_exit_rcu(). */
+
+	if ((new_count & HARDIRQ_DISABLE_MASK) == HARDIRQ_DISABLE_OFFSET)
+		_local_interrupt_disable();
+}
+
+static inline void local_interrupt_enable(void)
+{
+	int new_count;
+
+	/* Unpaired local_interrupt_enable()? Warn and abort. */
+	if (IS_ENABLED(CONFIG_DEBUG_PREEMPT) &&
+	    DEBUG_LOCKS_WARN_ON((preempt_count() & HARDIRQ_DISABLE_MASK) == 0))
+		return;
+
+	new_count = hardirq_disable_exit();
+
+	if ((new_count & HARDIRQ_DISABLE_MASK) == 0)
+		_local_interrupt_enable();
+}
+
+#endif /* !__LINUX_INTERRUPT_RC_H */
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index e2d3079d3f5f..33fc4c814a9f 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -151,6 +151,10 @@ static __always_inline unsigned char interrupt_context_level(void)
 #define in_softirq()		(softirq_count())
 #define in_interrupt()		(irq_count())
 
+#define hardirq_disable_count()	((preempt_count() & HARDIRQ_DISABLE_MASK) >> HARDIRQ_DISABLE_SHIFT)
+#define hardirq_disable_enter()	__preempt_count_add_return(HARDIRQ_DISABLE_OFFSET)
+#define hardirq_disable_exit()	__preempt_count_sub_return(HARDIRQ_DISABLE_OFFSET)
+
 /*
  * The preempt_count offset after preempt_disable();
  */
diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 241277cd34cf..3d405cc4c121 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -57,6 +57,7 @@
 #include <linux/linkage.h>
 #include <linux/compiler.h>
 #include <linux/irqflags.h>
+#include <linux/interrupt_rc.h>
 #include <linux/thread_info.h>
 #include <linux/stringify.h>
 #include <linux/bottom_half.h>
@@ -273,9 +274,11 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 #endif
 
 #define raw_spin_lock_irq(lock)		_raw_spin_lock_irq(lock)
+#define raw_spin_lock_irq_disable(lock)	_raw_spin_lock_irq_disable(lock)
 #define raw_spin_lock_bh(lock)		_raw_spin_lock_bh(lock)
 #define raw_spin_unlock(lock)		_raw_spin_unlock(lock)
 #define raw_spin_unlock_irq(lock)	_raw_spin_unlock_irq(lock)
+#define raw_spin_unlock_irq_enable(lock)	_raw_spin_unlock_irq_enable(lock)
 
 #define raw_spin_unlock_irqrestore(lock, flags)		\
 	do {							\
@@ -290,6 +293,8 @@ static inline void do_raw_spin_unlock(raw_spinlock_t *lock) __releases(lock)
 
 #define raw_spin_trylock_irqsave(lock, flags) _raw_spin_trylock_irqsave(lock, &(flags))
 
+#define raw_spin_trylock_irq_disable(lock)	_raw_spin_trylock_irq_disable(lock)
+
 #ifndef CONFIG_PREEMPT_RT
 /* Include rwlock functions for !RT */
 #include <linux/rwlock.h>
@@ -372,6 +377,12 @@ static __always_inline void spin_lock_irq(spinlock_t *lock)
 	raw_spin_lock_irq(&lock->rlock);
 }
 
+static __always_inline void spin_lock_irq_disable(spinlock_t *lock)
+	__acquires(lock) __no_context_analysis
+{
+	raw_spin_lock_irq_disable(&lock->rlock);
+}
+
 #define spin_lock_irqsave(lock, flags)				\
 do {								\
 	raw_spin_lock_irqsave(spinlock_check(lock), flags);	\
@@ -402,6 +413,12 @@ static __always_inline void spin_unlock_irq(spinlock_t *lock)
 	raw_spin_unlock_irq(&lock->rlock);
 }
 
+static __always_inline void spin_unlock_irq_enable(spinlock_t *lock)
+	__releases(lock) __no_context_analysis
+{
+	raw_spin_unlock_irq_enable(&lock->rlock);
+}
+
 static __always_inline void spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
 	__releases(lock) __no_context_analysis
 {
@@ -427,6 +444,12 @@ static __always_inline bool _spin_trylock_irqsave(spinlock_t *lock, unsigned lon
 }
 #define spin_trylock_irqsave(lock, flags) _spin_trylock_irqsave(lock, &(flags))
 
+static __always_inline int spin_trylock_irq_disable(spinlock_t *lock)
+	__cond_acquires(true, lock) __no_context_analysis
+{
+	return raw_spin_trylock_irq_disable(&lock->rlock);
+}
+
 /**
  * spin_is_locked() - Check whether a spinlock is locked.
  * @lock: Pointer to the spinlock.
diff --git a/include/linux/spinlock_api_smp.h b/include/linux/spinlock_api_smp.h
index bda5e7a390cd..90909d933dab 100644
--- a/include/linux/spinlock_api_smp.h
+++ b/include/linux/spinlock_api_smp.h
@@ -28,6 +28,8 @@ _raw_spin_lock_nest_lock(raw_spinlock_t *lock, struct lockdep_map *map)
 void __lockfunc _raw_spin_lock_bh(raw_spinlock_t *lock)		__acquires(lock);
 void __lockfunc _raw_spin_lock_irq(raw_spinlock_t *lock)
 								__acquires(lock);
+void __lockfunc _raw_spin_lock_irq_disable(raw_spinlock_t *lock)
+								__acquires(lock);
 
 unsigned long __lockfunc _raw_spin_lock_irqsave(raw_spinlock_t *lock)
 								__acquires(lock);
@@ -39,6 +41,7 @@ int __lockfunc _raw_spin_trylock_bh(raw_spinlock_t *lock)	__cond_acquires(true,
 void __lockfunc _raw_spin_unlock(raw_spinlock_t *lock)		__releases(lock);
 void __lockfunc _raw_spin_unlock_bh(raw_spinlock_t *lock)	__releases(lock);
 void __lockfunc _raw_spin_unlock_irq(raw_spinlock_t *lock)	__releases(lock);
+void __lockfunc _raw_spin_unlock_irq_enable(raw_spinlock_t *lock)	__releases(lock);
 void __lockfunc
 _raw_spin_unlock_irqrestore(raw_spinlock_t *lock, unsigned long flags)
 								__releases(lock);
@@ -55,6 +58,11 @@ _raw_spin_unlock_irqrestore(raw_spinlock_t *lock, unsigned long flags)
 #define _raw_spin_lock_irq(lock) __raw_spin_lock_irq(lock)
 #endif
 
+/* Use the same config as spin_lock_irq() temporarily. */
+#ifdef CONFIG_INLINE_SPIN_LOCK_IRQ
+#define _raw_spin_lock_irq_disable(lock) __raw_spin_lock_irq_disable(lock)
+#endif
+
 #ifdef CONFIG_INLINE_SPIN_LOCK_IRQSAVE
 #define _raw_spin_lock_irqsave(lock) __raw_spin_lock_irqsave(lock)
 #endif
@@ -79,6 +87,11 @@ _raw_spin_unlock_irqrestore(raw_spinlock_t *lock, unsigned long flags)
 #define _raw_spin_unlock_irq(lock) __raw_spin_unlock_irq(lock)
 #endif
 
+/* Use the same config as spin_unlock_irq() temporarily. */
+#ifdef CONFIG_INLINE_SPIN_UNLOCK_IRQ
+#define _raw_spin_unlock_irq_enable(lock) __raw_spin_unlock_irq_enable(lock)
+#endif
+
 #ifdef CONFIG_INLINE_SPIN_UNLOCK_IRQRESTORE
 #define _raw_spin_unlock_irqrestore(lock, flags) __raw_spin_unlock_irqrestore(lock, flags)
 #endif
@@ -105,6 +118,16 @@ static __always_inline bool _raw_spin_trylock_irq(raw_spinlock_t *lock)
 	return false;
 }
 
+static __always_inline bool _raw_spin_trylock_irq_disable(raw_spinlock_t *lock)
+	__cond_acquires(true, lock)
+{
+	local_interrupt_disable();
+	if (_raw_spin_trylock(lock))
+		return true;
+	local_interrupt_enable();
+	return false;
+}
+
 static __always_inline bool _raw_spin_trylock_irqsave(raw_spinlock_t *lock, unsigned long *flags)
 	__cond_acquires(true, lock)
 {
@@ -143,6 +166,15 @@ static inline void __raw_spin_lock_irq(raw_spinlock_t *lock)
 	LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
 }
 
+static inline void __raw_spin_lock_irq_disable(raw_spinlock_t *lock)
+	__acquires(lock) __no_context_analysis
+{
+	local_interrupt_disable();
+	preempt_disable();
+	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
+	LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
+}
+
 static inline void __raw_spin_lock_bh(raw_spinlock_t *lock)
 	__acquires(lock) __no_context_analysis
 {
@@ -188,6 +220,15 @@ static inline void __raw_spin_unlock_irq(raw_spinlock_t *lock)
 	preempt_enable();
 }
 
+static inline void __raw_spin_unlock_irq_enable(raw_spinlock_t *lock)
+	__releases(lock)
+{
+	spin_release(&lock->dep_map, _RET_IP_);
+	do_raw_spin_unlock(lock);
+	local_interrupt_enable();
+	preempt_enable();
+}
+
 static inline void __raw_spin_unlock_bh(raw_spinlock_t *lock)
 	__releases(lock)
 {
diff --git a/include/linux/spinlock_api_up.h b/include/linux/spinlock_api_up.h
index a9d5c7c66e03..d03d3065ee04 100644
--- a/include/linux/spinlock_api_up.h
+++ b/include/linux/spinlock_api_up.h
@@ -42,6 +42,9 @@
 #define __LOCK_IRQSAVE(lock, flags, ...) \
   do { local_irq_save(flags); __LOCK(lock, ##__VA_ARGS__); } while (0)
 
+#define __LOCK_IRQ_DISABLE(lock, ...) \
+  do { local_interrupt_disable(); __LOCK(lock, ##__VA_ARGS__); } while (0)
+
 #define ___UNLOCK_(lock) \
   do { __release(lock); (void)(lock); } while (0)
 
@@ -61,6 +64,9 @@
 #define __UNLOCK_IRQRESTORE(lock, flags, ...) \
   do { local_irq_restore(flags); __UNLOCK(lock, ##__VA_ARGS__); } while (0)
 
+#define __UNLOCK_IRQ_ENABLE(lock, ...) \
+  do { __UNLOCK(lock, ##__VA_ARGS__); local_interrupt_enable(); } while (0)
+
 #define _raw_spin_lock(lock)			__LOCK(lock)
 #define _raw_spin_lock_nested(lock, subclass)	__LOCK(lock)
 #define _raw_read_lock(lock)			__LOCK(lock, shared)
@@ -70,6 +76,7 @@
 #define _raw_read_lock_bh(lock)			__LOCK_BH(lock, shared)
 #define _raw_write_lock_bh(lock)		__LOCK_BH(lock)
 #define _raw_spin_lock_irq(lock)		__LOCK_IRQ(lock)
+#define _raw_spin_lock_irq_disable(lock)	__LOCK_IRQ_DISABLE(lock)
 #define _raw_read_lock_irq(lock)		__LOCK_IRQ(lock, shared)
 #define _raw_write_lock_irq(lock)		__LOCK_IRQ(lock)
 #define _raw_spin_lock_irqsave(lock, flags)	__LOCK_IRQSAVE(lock, flags)
@@ -97,6 +104,13 @@ static __always_inline int _raw_spin_trylock_irq(raw_spinlock_t *lock)
 	return 1;
 }
 
+static __always_inline int _raw_spin_trylock_irq_disable(raw_spinlock_t *lock)
+	__cond_acquires(true, lock)
+{
+	__LOCK_IRQ_DISABLE(lock);
+	return 1;
+}
+
 static __always_inline int _raw_spin_trylock_irqsave(raw_spinlock_t *lock, unsigned long *flags)
 	__cond_acquires(true, lock)
 {
@@ -132,6 +146,7 @@ static __always_inline int _raw_write_trylock_irqsave(rwlock_t *lock, unsigned l
 #define _raw_write_unlock_bh(lock)		__UNLOCK_BH(lock)
 #define _raw_read_unlock_bh(lock)		__UNLOCK_BH(lock, shared)
 #define _raw_spin_unlock_irq(lock)		__UNLOCK_IRQ(lock)
+#define _raw_spin_unlock_irq_enable(lock)	__UNLOCK_IRQ_ENABLE(lock)
 #define _raw_read_unlock_irq(lock)		__UNLOCK_IRQ(lock, shared)
 #define _raw_write_unlock_irq(lock)		__UNLOCK_IRQ(lock)
 #define _raw_spin_unlock_irqrestore(lock, flags) \
diff --git a/include/linux/spinlock_rt.h b/include/linux/spinlock_rt.h
index 373618a4243c..560d06384e0c 100644
--- a/include/linux/spinlock_rt.h
+++ b/include/linux/spinlock_rt.h
@@ -96,6 +96,12 @@ static __always_inline void spin_lock_irq(spinlock_t *lock)
 	rt_spin_lock(lock);
 }
 
+static __always_inline void spin_lock_irq_disable(spinlock_t *lock)
+	__acquires(lock)
+{
+	rt_spin_lock(lock);
+}
+
 #define spin_lock_irqsave(lock, flags)			 \
 	do {						 \
 		typecheck(unsigned long, flags);	 \
@@ -122,6 +128,12 @@ static __always_inline void spin_unlock_irq(spinlock_t *lock)
 	rt_spin_unlock(lock);
 }
 
+static __always_inline void spin_unlock_irq_enable(spinlock_t *lock)
+	__releases(lock)
+{
+	rt_spin_unlock(lock);
+}
+
 static __always_inline void spin_unlock_irqrestore(spinlock_t *lock,
 						   unsigned long flags)
 	__releases(lock)
@@ -131,6 +143,12 @@ static __always_inline void spin_unlock_irqrestore(spinlock_t *lock,
 
 #define spin_trylock(lock)	rt_spin_trylock(lock)
 
+static __always_inline int spin_trylock_irq_disable(spinlock_t *lock)
+	__cond_acquires(true, lock)
+{
+	return rt_spin_trylock(lock);
+}
+
 #define spin_trylock_bh(lock)	rt_spin_trylock_bh(lock)
 
 #define spin_trylock_irq(lock)	rt_spin_trylock(lock)
diff --git a/kernel/locking/spinlock.c b/kernel/locking/spinlock.c
index b42d293da38b..83a17eaf5717 100644
--- a/kernel/locking/spinlock.c
+++ b/kernel/locking/spinlock.c
@@ -129,6 +129,21 @@ static void __lockfunc __raw_##op##_lock_bh(locktype##_t *lock)		\
  */
 BUILD_LOCK_OPS(spin, raw_spinlock, __acquires);
 
+/* No rwlock_t variants for now, so just build this function by hand */
+static void __lockfunc __raw_spin_lock_irq_disable(raw_spinlock_t *lock)
+{
+	for (;;) {
+		preempt_disable();
+		local_interrupt_disable();
+		if (likely(do_raw_spin_trylock(lock)))
+			break;
+		local_interrupt_enable();
+		preempt_enable();
+
+		arch_spin_relax(&lock->raw_lock);
+	}
+}
+
 #ifndef CONFIG_PREEMPT_RT
 BUILD_LOCK_OPS(read, rwlock, __acquires_shared);
 BUILD_LOCK_OPS(write, rwlock, __acquires);
@@ -176,6 +191,14 @@ noinline void __lockfunc _raw_spin_lock_irq(raw_spinlock_t *lock)
 EXPORT_SYMBOL(_raw_spin_lock_irq);
 #endif
 
+#ifndef CONFIG_INLINE_SPIN_LOCK_IRQ
+noinline void __lockfunc _raw_spin_lock_irq_disable(raw_spinlock_t *lock)
+{
+	__raw_spin_lock_irq_disable(lock);
+}
+EXPORT_SYMBOL_GPL(_raw_spin_lock_irq_disable);
+#endif
+
 #ifndef CONFIG_INLINE_SPIN_LOCK_BH
 noinline void __lockfunc _raw_spin_lock_bh(raw_spinlock_t *lock)
 {
@@ -208,6 +231,14 @@ noinline void __lockfunc _raw_spin_unlock_irq(raw_spinlock_t *lock)
 EXPORT_SYMBOL(_raw_spin_unlock_irq);
 #endif
 
+#ifndef CONFIG_INLINE_SPIN_UNLOCK_IRQ
+noinline void __lockfunc _raw_spin_unlock_irq_enable(raw_spinlock_t *lock)
+{
+	__raw_spin_unlock_irq_enable(lock);
+}
+EXPORT_SYMBOL_GPL(_raw_spin_unlock_irq_enable);
+#endif
+
 #ifndef CONFIG_INLINE_SPIN_UNLOCK_BH
 noinline void __lockfunc _raw_spin_unlock_bh(raw_spinlock_t *lock)
 {
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 10af5ed859e7..0c9b2269a8d6 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -9,6 +9,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#define INSTANTIATE_EXPORTED_INTERRUPT_DISABLE
 #include <linux/export.h>
 #include <linux/kernel_stat.h>
 #include <linux/interrupt.h>
@@ -88,6 +89,20 @@ EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabled);
 EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
 #endif
 
+DEFINE_PER_CPU(unsigned long, local_interrupt_disable_state);
+
+void _local_interrupt_disable(void)
+{
+	__local_interrupt_disable();
+}
+EXPORT_SYMBOL(_local_interrupt_disable);
+
+void _local_interrupt_enable(void)
+{
+	__local_interrupt_enable();
+}
+EXPORT_SYMBOL(_local_interrupt_enable);
+
 DEFINE_PER_CPU(unsigned int, nmi_nesting);
 
 /*
@@ -728,10 +743,19 @@ static inline void __irq_exit_rcu(void)
 #endif
 	account_hardirq_exit(current);
 	preempt_count_sub(HARDIRQ_OFFSET);
-	if (!in_interrupt() && local_softirq_pending()) {
+	/*
+	 * Interrupts may happen between hardirq_disable_enter() and
+	 * local_irq_save() in local_interrupt_disable(), if irq_exit() invokes
+	 * softirq here, we may have a softirq handler calling
+	 * local_interrupt_disable() but it won't disable the IRQ because
+	 * hardirq disabling count is already 1, hence we need to prevent
+	 * invoking softirq when a local_interrupt_disable() is ongoing.
+	 */
+	if (!in_interrupt() && !hardirq_disable_count() &&
+	    local_softirq_pending()) {
 		/*
 		 * If we left hrtimers unarmed, make sure to arm them now,
-		 * before enabling interrupts to run SoftIRQ.
+		 * before enabling interrupts to run softirq.
 		 */
 		hrtimer_rearm_deferred();
 		invoke_softirq();
-- 
2.50.1 (Apple Git-155)

[PATCH v5 06/18] irq: Add KUnit test for refcounted interrupt enable/disable

[Boqun Feng]

From: Lyude Paul <lyude@redhat.com>

While making changes to the refcounted interrupt patch series, at some
point on my local branch I broke something and ended up writing some kunit
tests for testing refcounted interrupts as a result. So, let's include
these tests now that we have refcounted interrupts.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 kernel/irq/Makefile                  |   1 +
 kernel/irq/refcount_interrupt_test.c | 109 +++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 kernel/irq/refcount_interrupt_test.c

diff --git a/kernel/irq/Makefile b/kernel/irq/Makefile
index 86a2e5ae08f9..44c4d6fc502a 100644
--- a/kernel/irq/Makefile
+++ b/kernel/irq/Makefile
@@ -16,3 +16,4 @@ obj-$(CONFIG_SMP) += affinity.o
 obj-$(CONFIG_GENERIC_IRQ_DEBUGFS) += debugfs.o
 obj-$(CONFIG_GENERIC_IRQ_MATRIX_ALLOCATOR) += matrix.o
 obj-$(CONFIG_IRQ_KUNIT_TEST) += irq_test.o
+obj-$(CONFIG_KUNIT) += refcount_interrupt_test.o
diff --git a/kernel/irq/refcount_interrupt_test.c b/kernel/irq/refcount_interrupt_test.c
new file mode 100644
index 000000000000..ca904dba24b9
--- /dev/null
+++ b/kernel/irq/refcount_interrupt_test.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for refcounted interrupt enable/disables.
+ */
+
+#include <kunit/test.h>
+#include <linux/interrupt_rc.h>
+
+#define TEST_IRQ_ON() KUNIT_EXPECT_FALSE(test, irqs_disabled())
+#define TEST_IRQ_OFF() KUNIT_EXPECT_TRUE(test, irqs_disabled())
+
+/* ===== Test cases ===== */
+static void test_single_irq_change(struct kunit *test)
+{
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+	local_interrupt_enable();
+}
+
+static void test_nested_irq_change(struct kunit *test)
+{
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+
+	local_interrupt_enable();
+	TEST_IRQ_OFF();
+	local_interrupt_enable();
+	TEST_IRQ_OFF();
+	local_interrupt_enable();
+	TEST_IRQ_ON();
+}
+
+static void test_multiple_irq_change(struct kunit *test)
+{
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+
+	local_interrupt_enable();
+	TEST_IRQ_OFF();
+	local_interrupt_enable();
+	TEST_IRQ_ON();
+
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+	local_interrupt_enable();
+	TEST_IRQ_ON();
+}
+
+static void test_irq_save(struct kunit *test)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	TEST_IRQ_OFF();
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+	local_interrupt_enable();
+	TEST_IRQ_OFF();
+	local_irq_restore(flags);
+	TEST_IRQ_ON();
+
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+	local_irq_save(flags);
+	TEST_IRQ_OFF();
+	local_irq_restore(flags);
+	TEST_IRQ_OFF();
+	local_interrupt_enable();
+	TEST_IRQ_ON();
+}
+
+static struct kunit_case test_cases[] = {
+	KUNIT_CASE(test_single_irq_change),
+	KUNIT_CASE(test_nested_irq_change),
+	KUNIT_CASE(test_multiple_irq_change),
+	KUNIT_CASE(test_irq_save),
+	{},
+};
+
+/* init and exit are the same. */
+static int test_init(struct kunit *test)
+{
+	TEST_IRQ_ON();
+
+	return 0;
+}
+
+static void test_exit(struct kunit *test)
+{
+	TEST_IRQ_ON();
+}
+
+static struct kunit_suite refcount_interrupt_test_suite = {
+	.name = "refcount_interrupt",
+	.test_cases = test_cases,
+	.init = test_init,
+	.exit = test_exit,
+};
+
+kunit_test_suite(refcount_interrupt_test_suite);
+MODULE_AUTHOR("Lyude Paul <lyude@redhat.com>");
+MODULE_DESCRIPTION("Refcounted interrupt unit test suite");
+MODULE_LICENSE("GPL");
-- 
2.50.1 (Apple Git-155)

[PATCH v5 07/18] irq: Add max local_interrupt_disable() nesting level kunit test case

[Boqun Feng]

To confirm the max nesting level of local_interrupt_disable() works, a
kunit test is added to the whole test suite.

Note that when DEBUG_PREEMPT=y, it'll generate a warning which is
expected.

Suggested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 kernel/irq/refcount_interrupt_test.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/kernel/irq/refcount_interrupt_test.c b/kernel/irq/refcount_interrupt_test.c
index ca904dba24b9..38dfccbaa4d4 100644
--- a/kernel/irq/refcount_interrupt_test.c
+++ b/kernel/irq/refcount_interrupt_test.c
@@ -52,6 +52,27 @@ static void test_multiple_irq_change(struct kunit *test)
 	TEST_IRQ_ON();
 }
 
+static void test_max_nesting_irq_change(struct kunit *test)
+{
+	for (int i = 0; i < __IRQ_MASK(HARDIRQ_DISABLE_BITS); i++) {
+		local_interrupt_disable();
+		TEST_IRQ_OFF();
+	}
+
+
+	for (int i = 0; i < __IRQ_MASK(HARDIRQ_DISABLE_BITS); i++) {
+		TEST_IRQ_OFF();
+		local_interrupt_enable();
+	}
+
+	TEST_IRQ_ON();
+
+	local_interrupt_disable();
+	TEST_IRQ_OFF();
+	local_interrupt_enable();
+	TEST_IRQ_ON();
+}
+
 static void test_irq_save(struct kunit *test)
 {
 	unsigned long flags;
@@ -79,6 +100,7 @@ static struct kunit_case test_cases[] = {
 	KUNIT_CASE(test_single_irq_change),
 	KUNIT_CASE(test_nested_irq_change),
 	KUNIT_CASE(test_multiple_irq_change),
+	KUNIT_CASE(test_max_nesting_irq_change),
 	KUNIT_CASE(test_irq_save),
 	{},
 };
-- 
2.50.1 (Apple Git-155)

[PATCH v5 08/18] locking: Switch to _irq_{disable,enable}() variants in cleanup guards

[Boqun Feng]

The semantics of various IRQ disabling guards match what
*_irq_{disable,enable}() provide, i.e. the interrupt disabling is
properly nested, therefore it's OK to switch to use
*_irq_{disable,enable}() primitives.

[boqun: Adjust the user-side changes in do_sched_cfs_*_timer() provided
by Peter and Lyude]

Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 include/linux/spinlock.h | 26 ++++++++++++--------------
 kernel/sched/fair.c      | 12 ++++++------
 2 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 3d405cc4c121..799a8f7d2741 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -572,12 +572,12 @@ DECLARE_LOCK_GUARD_1_ATTRS(raw_spinlock_nested, __acquires(_T), __releases(*(raw
 #define class_raw_spinlock_nested_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(raw_spinlock_nested, _T)
 
 DEFINE_LOCK_GUARD_1(raw_spinlock_irq, raw_spinlock_t,
-		    raw_spin_lock_irq(_T->lock),
-		    raw_spin_unlock_irq(_T->lock))
+		    raw_spin_lock_irq_disable(_T->lock),
+		    raw_spin_unlock_irq_enable(_T->lock))
 DECLARE_LOCK_GUARD_1_ATTRS(raw_spinlock_irq, __acquires(_T), __releases(*(raw_spinlock_t **)_T))
 #define class_raw_spinlock_irq_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(raw_spinlock_irq, _T)
 
-DEFINE_LOCK_GUARD_1_COND(raw_spinlock_irq, _try, raw_spin_trylock_irq(_T->lock))
+DEFINE_LOCK_GUARD_1_COND(raw_spinlock_irq, _try, raw_spin_trylock_irq_disable(_T->lock))
 DECLARE_LOCK_GUARD_1_ATTRS(raw_spinlock_irq_try, __acquires(_T), __releases(*(raw_spinlock_t **)_T))
 #define class_raw_spinlock_irq_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(raw_spinlock_irq_try, _T)
 
@@ -592,14 +592,13 @@ DECLARE_LOCK_GUARD_1_ATTRS(raw_spinlock_bh_try, __acquires(_T), __releases(*(raw
 #define class_raw_spinlock_bh_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(raw_spinlock_bh_try, _T)
 
 DEFINE_LOCK_GUARD_1(raw_spinlock_irqsave, raw_spinlock_t,
-		    raw_spin_lock_irqsave(_T->lock, _T->flags),
-		    raw_spin_unlock_irqrestore(_T->lock, _T->flags),
-		    unsigned long flags)
+		    raw_spin_lock_irq_disable(_T->lock),
+		    raw_spin_unlock_irq_enable(_T->lock))
 DECLARE_LOCK_GUARD_1_ATTRS(raw_spinlock_irqsave, __acquires(_T), __releases(*(raw_spinlock_t **)_T))
 #define class_raw_spinlock_irqsave_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(raw_spinlock_irqsave, _T)
 
 DEFINE_LOCK_GUARD_1_COND(raw_spinlock_irqsave, _try,
-			 raw_spin_trylock_irqsave(_T->lock, _T->flags))
+			 raw_spin_trylock_irq_disable(_T->lock))
 DECLARE_LOCK_GUARD_1_ATTRS(raw_spinlock_irqsave_try, __acquires(_T), __releases(*(raw_spinlock_t **)_T))
 #define class_raw_spinlock_irqsave_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(raw_spinlock_irqsave_try, _T)
 
@@ -618,13 +617,13 @@ DECLARE_LOCK_GUARD_1_ATTRS(spinlock_try, __acquires(_T), __releases(*(spinlock_t
 #define class_spinlock_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(spinlock_try, _T)
 
 DEFINE_LOCK_GUARD_1(spinlock_irq, spinlock_t,
-		    spin_lock_irq(_T->lock),
-		    spin_unlock_irq(_T->lock))
+		    spin_lock_irq_disable(_T->lock),
+		    spin_unlock_irq_enable(_T->lock))
 DECLARE_LOCK_GUARD_1_ATTRS(spinlock_irq, __acquires(_T), __releases(*(spinlock_t **)_T))
 #define class_spinlock_irq_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(spinlock_irq, _T)
 
 DEFINE_LOCK_GUARD_1_COND(spinlock_irq, _try,
-			 spin_trylock_irq(_T->lock))
+			 spin_trylock_irq_disable(_T->lock))
 DECLARE_LOCK_GUARD_1_ATTRS(spinlock_irq_try, __acquires(_T), __releases(*(spinlock_t **)_T))
 #define class_spinlock_irq_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(spinlock_irq_try, _T)
 
@@ -640,14 +639,13 @@ DECLARE_LOCK_GUARD_1_ATTRS(spinlock_bh_try, __acquires(_T), __releases(*(spinloc
 #define class_spinlock_bh_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(spinlock_bh_try, _T)
 
 DEFINE_LOCK_GUARD_1(spinlock_irqsave, spinlock_t,
-		    spin_lock_irqsave(_T->lock, _T->flags),
-		    spin_unlock_irqrestore(_T->lock, _T->flags),
-		    unsigned long flags)
+		    spin_lock_irq_disable(_T->lock),
+		    spin_unlock_irq_enable(_T->lock))
 DECLARE_LOCK_GUARD_1_ATTRS(spinlock_irqsave, __acquires(_T), __releases(*(spinlock_t **)_T))
 #define class_spinlock_irqsave_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(spinlock_irqsave, _T)
 
 DEFINE_LOCK_GUARD_1_COND(spinlock_irqsave, _try,
-			 spin_trylock_irqsave(_T->lock, _T->flags))
+			 spin_trylock_irq_disable(_T->lock))
 DECLARE_LOCK_GUARD_1_ATTRS(spinlock_irqsave_try, __acquires(_T), __releases(*(spinlock_t **)_T))
 #define class_spinlock_irqsave_try_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(spinlock_irqsave_try, _T)
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d78467ec6ee1..a46c4ff49f74 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7120,7 +7120,7 @@ static bool distribute_cfs_runtime(struct cfs_bandwidth *cfs_b)
  * period the timer is deactivated until scheduling resumes; cfs_b->idle is
  * used to track this state.
  */
-static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun, unsigned long flags)
+static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
 	__must_hold(&cfs_b->lock)
 {
 	int throttled;
@@ -7155,10 +7155,10 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun, u
 	 * This check is repeated as we release cfs_b->lock while we unthrottle.
 	 */
 	while (throttled && cfs_b->runtime > 0) {
-		raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
+		raw_spin_unlock_irq_enable(&cfs_b->lock);
 		/* we can't nest cfs_b->lock while distributing bandwidth */
 		throttled = distribute_cfs_runtime(cfs_b);
-		raw_spin_lock_irqsave(&cfs_b->lock, flags);
+		raw_spin_lock_irq_disable(&cfs_b->lock);
 	}
 
 	/*
@@ -7266,7 +7266,7 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
 {
 	/* confirm we're still not at a refresh boundary */
-	scoped_guard(raw_spinlock_irqsave, &cfs_b->lock) {
+	scoped_guard(raw_spinlock_irq, &cfs_b->lock) {
 		u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
 
 		cfs_b->slack_started = false;
@@ -7351,14 +7351,14 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
 	int idle = 0;
 	int count = 0;
 
-	CLASS(raw_spinlock_irqsave, cfsb_guard)(&cfs_b->lock);
+	guard(raw_spinlock_irq)(&cfs_b->lock);
 
 	for (;;) {
 		overrun = hrtimer_forward_now(timer, cfs_b->period);
 		if (!overrun)
 			break;
 
-		idle = do_sched_cfs_period_timer(cfs_b, overrun, cfsb_guard.flags);
+		idle = do_sched_cfs_period_timer(cfs_b, overrun);
 
 		if (++count > 3) {
 			u64 new, old = ktime_to_ns(cfs_b->period);
-- 
2.50.1 (Apple Git-155)

[PATCH v5 09/18] sched: Remove the unused preempt_offset parameter of __cant_sleep()

[Boqun Feng]

The preempt_offset is always 0 in all the callsites of __cant_sleep(),
hence remove it. It also allows us to clear up the code a bit by
no longer using a "preempt_count() > .." comparison.

Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 include/linux/kernel.h | 4 ++--
 kernel/sched/core.c    | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index e5570a16cbb1..24414c79e59a 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -72,7 +72,7 @@ extern int dynamic_might_resched(void);
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 extern void __might_resched(const char *file, int line, unsigned int offsets);
 extern void __might_sleep(const char *file, int line);
-extern void __cant_sleep(const char *file, int line, int preempt_offset);
+extern void __cant_sleep(const char *file, int line);
 extern void __cant_migrate(const char *file, int line);
 
 /**
@@ -95,7 +95,7 @@ extern void __cant_migrate(const char *file, int line);
  * this macro will print a stack trace if it is executed with preemption enabled
  */
 # define cant_sleep() \
-	do { __cant_sleep(__FILE__, __LINE__, 0); } while (0)
+	do { __cant_sleep(__FILE__, __LINE__); } while (0)
 # define sched_annotate_sleep()	(current->task_state_change = 0)
 
 /**
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 96226707c2f6..aa116daf21bd 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9199,7 +9199,7 @@ void __might_resched(const char *file, int line, unsigned int offsets)
 }
 EXPORT_SYMBOL(__might_resched);
 
-void __cant_sleep(const char *file, int line, int preempt_offset)
+void __cant_sleep(const char *file, int line)
 {
 	static unsigned long prev_jiffy;
 
@@ -9209,7 +9209,7 @@ void __cant_sleep(const char *file, int line, int preempt_offset)
 	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
 		return;
 
-	if (preempt_count() > preempt_offset)
+	if (preempt_count())
 		return;
 
 	if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
-- 
2.50.1 (Apple Git-155)

[PATCH v5 10/18] sched: Avoid signed comparison of preempt_count() in __cant_migrate()

[Boqun Feng]

Currently preempt_count() is always a non-negative int on all archs
(PREEMPT_NEED_RESCHED archs will mask out the MSB when returning
preempt_count()), hence the checking in __cant_migrate() is in fact just
checking whether preempt_count() is 0 or not. In a future change, we are
going to use all the 32 bits of preempt_count(), which would make
negative int values possible from preempt_count(). Therefore convert the
"> 0" comparison into a zero check to prepare for the future change.
No functional changes are intended.

Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index aa116daf21bd..9b3f1764fa9e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9241,7 +9241,7 @@ void __cant_migrate(const char *file, int line)
 	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
 		return;
 
-	if (preempt_count() > 0)
+	if (preempt_count())
 		return;
 
 	if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
-- 
2.50.1 (Apple Git-155)

[PATCH v5 11/18] preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS

[Boqun Feng]

With the changes that enable preempt count to track IRQ disabling
nesting, we don't have enough bits in 32-bit preempt count
implementation, as a result we move NMI nesting bits out of the 32-bit
preempt count. However on the architectures that can support 64-bit
preempt count implementation, we can keep the NMI nesting bits in the
32-bit preempt count and avoid maintaining NMI nesting bits outside of
the same cache line.

Therefore HAS_SEPARATE_PREEMPT_RESCHED_BITS is introduced to allow
architectures to select this. Note that under this Kconfig, preempt
count is maintained in a 64-bit word however preempt_count() still
remains as an int because all the effective bits still fit in
(previously we mask out NEED_RESCHED bit in preempt_count()). This
should make no functional changes for existing preempt_count() users.

Enable this for x86_64 along with the introduction of the Kconfig.

[boqun: Undo the __preempt_count_{add,sub}() optimization in 32-bit
preempt count since it may introduce {over,under}flow]

[boqun: Address the feedback from Shrikanth]

Originally-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 arch/x86/Kconfig                              |  1 +
 arch/x86/include/asm/preempt.h                | 55 +++++++++++++------
 arch/x86/kernel/cpu/common.c                  |  2 +-
 include/linux/hardirq.h                       | 47 +++++++++++-----
 include/linux/preempt.h                       | 23 +++++++-
 kernel/Kconfig.preempt                        |  4 ++
 kernel/sched/core.c                           | 12 +++-
 kernel/softirq.c                              |  6 ++
 .../testing/selftests/bpf/bpf_experimental.h  |  2 +-
 9 files changed, 115 insertions(+), 37 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bdad90f210e4..6a7067d20a6a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -326,6 +326,7 @@ config X86
 	select USER_STACKTRACE_SUPPORT
 	select HAVE_ARCH_KCSAN			if X86_64
 	select PROC_PID_ARCH_STATUS		if PROC_FS
+	select HAS_SEPARATE_PREEMPT_RESCHED_BITS		if X86_64 && PREEMPT_COUNT
 	select HAVE_ARCH_NODE_DEV_GROUP		if X86_SGX
 	select FUNCTION_ALIGNMENT_16B		if X86_64 || X86_ALIGNMENT_16
 	select FUNCTION_ALIGNMENT_4B
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index 1220656f3370..022838589d2a 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -7,10 +7,20 @@
 
 #include <linux/static_call_types.h>
 
-DECLARE_PER_CPU_CACHE_HOT(int, __preempt_count);
+DECLARE_PER_CPU_CACHE_HOT(unsigned long, __preempt_count);
 
-/* We use the MSB mostly because its available */
-#define PREEMPT_NEED_RESCHED	0x80000000
+/*
+ * We use the MSB for PREEMPT_NEED_RESCHED mostly because it is available.
+ */
+#define PREEMPT_NEED_RESCHED	(~(((unsigned long)-1L) >> 1))
+
+#ifdef CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS
+#define __pc_dec		"decq"
+#define __pc_op(op, ...)	raw_cpu_##op##_8(__VA_ARGS__)
+#else
+#define __pc_dec		"decl"
+#define __pc_op(op, ...)	raw_cpu_##op##_4(__VA_ARGS__)
+#endif
 
 /*
  * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
@@ -24,18 +34,26 @@ DECLARE_PER_CPU_CACHE_HOT(int, __preempt_count);
  */
 static __always_inline int preempt_count(void)
 {
-	return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
+	return __pc_op(read, __preempt_count) & ~PREEMPT_NEED_RESCHED;
 }
 
-static __always_inline void preempt_count_set(int pc)
+/*
+ * unsigned long preempt count parameter works for both 32bit and 64bit cases:
+ *
+ * - For 32bit, "int" (the return of preempt_count()) and "unsigned long" have
+ *   the same size.
+ * - For 64bit, the effective bits of a preempt count sits in 32bit, and we
+ *   preserve the NEED_RESCHED bit from the old count.
+ */
+static __always_inline void preempt_count_set(unsigned long pc)
 {
-	int old, new;
+	unsigned long old, new;
 
-	old = raw_cpu_read_4(__preempt_count);
+	old = __pc_op(read, __preempt_count);
 	do {
 		new = (old & PREEMPT_NEED_RESCHED) |
 			(pc & ~PREEMPT_NEED_RESCHED);
-	} while (!raw_cpu_try_cmpxchg_4(__preempt_count, &old, new));
+	} while (!__pc_op(try_cmpxchg, __preempt_count, &old, new));
 }
 
 /*
@@ -58,17 +76,17 @@ static __always_inline void preempt_count_set(int pc)
 
 static __always_inline void set_preempt_need_resched(void)
 {
-	raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
+	__pc_op(and, __preempt_count, ~PREEMPT_NEED_RESCHED);
 }
 
 static __always_inline void clear_preempt_need_resched(void)
 {
-	raw_cpu_or_4(__preempt_count, PREEMPT_NEED_RESCHED);
+	__pc_op(or, __preempt_count, PREEMPT_NEED_RESCHED);
 }
 
 static __always_inline bool test_preempt_need_resched(void)
 {
-	return !(raw_cpu_read_4(__preempt_count) & PREEMPT_NEED_RESCHED);
+	return !(__pc_op(read, __preempt_count) & PREEMPT_NEED_RESCHED);
 }
 
 /*
@@ -77,22 +95,22 @@ static __always_inline bool test_preempt_need_resched(void)
 
 static __always_inline void __preempt_count_add(int val)
 {
-	raw_cpu_add_4(__preempt_count, val);
+	__pc_op(add, __preempt_count, val);
 }
 
 static __always_inline void __preempt_count_sub(int val)
 {
-	raw_cpu_add_4(__preempt_count, -val);
+	__pc_op(add, __preempt_count, -val);
 }
 
 static __always_inline int __preempt_count_add_return(int val)
 {
-	return raw_cpu_add_return_4(__preempt_count, val);
+	return __pc_op(add_return, __preempt_count, val);
 }
 
 static __always_inline int __preempt_count_sub_return(int val)
 {
-	return raw_cpu_add_return_4(__preempt_count, -val);
+	return __pc_op(add_return, __preempt_count, -val);
 }
 
 /*
@@ -102,7 +120,7 @@ static __always_inline int __preempt_count_sub_return(int val)
  */
 static __always_inline bool __preempt_count_dec_and_test(void)
 {
-	return GEN_UNARY_RMWcc("decl", __my_cpu_var(__preempt_count), e,
+	return GEN_UNARY_RMWcc(__pc_dec, __my_cpu_var(__preempt_count), e,
 			       __percpu_arg([var]));
 }
 
@@ -111,7 +129,7 @@ static __always_inline bool __preempt_count_dec_and_test(void)
  */
 static __always_inline bool should_resched(int preempt_offset)
 {
-	return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
+	return unlikely(__pc_op(read, __preempt_count) == preempt_offset);
 }
 
 #ifdef CONFIG_PREEMPTION
@@ -158,4 +176,7 @@ do { \
 
 #endif /* PREEMPTION */
 
+#undef __pc_op
+#undef __pc_dec
+
 #endif /* __ASM_PREEMPT_H */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a3df21d26460..73a6d9f6a78e 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2236,7 +2236,7 @@ DEFINE_PER_CPU_CACHE_HOT(struct task_struct *, current_task) = &init_task;
 EXPORT_PER_CPU_SYMBOL(current_task);
 EXPORT_PER_CPU_SYMBOL(const_current_task);
 
-DEFINE_PER_CPU_CACHE_HOT(int, __preempt_count) = INIT_PREEMPT_COUNT;
+DEFINE_PER_CPU_CACHE_HOT(unsigned long, __preempt_count) = INIT_PREEMPT_COUNT;
 EXPORT_PER_CPU_SYMBOL(__preempt_count);
 
 DEFINE_PER_CPU_CACHE_HOT(unsigned long, cpu_current_top_of_stack) = TOP_OF_INIT_STACK;
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 8d4895531a45..860895a7f4e2 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -10,8 +10,6 @@
 #include <linux/vtime.h>
 #include <asm/hardirq.h>
 
-DECLARE_PER_CPU(unsigned int, nmi_nesting);
-
 extern void synchronize_irq(unsigned int irq);
 extern bool synchronize_hardirq(unsigned int irq);
 
@@ -94,6 +92,37 @@ void irq_exit_rcu(void);
 #define arch_nmi_exit()		do { } while (0)
 #endif
 
+#ifdef CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS
+static __always_inline void __preempt_count_nmi_enter(void)
+{
+	__preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET);
+}
+
+static __always_inline void __preempt_count_nmi_exit(void)
+{
+	__preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET);
+}
+#else
+DECLARE_PER_CPU(unsigned int, nmi_nesting);
+
+#define __preempt_count_nmi_enter()				\
+	do {							\
+		__preempt_count_add(HARDIRQ_OFFSET);		\
+		/* NMI nesting is represented in 4 bits. */     \
+		BUG_ON(__this_cpu_read(nmi_nesting) >= 15);	\
+		__this_cpu_inc(nmi_nesting);			\
+		preempt_count_set(preempt_count() | NMI_MASK);  \
+	} while (0)
+
+#define __preempt_count_nmi_exit()				\
+	do {							\
+		__preempt_count_sub(HARDIRQ_OFFSET);		\
+		if (!__this_cpu_dec_return(nmi_nesting))	\
+			preempt_count_set(preempt_count() & ~NMI_MASK); \
+	} while (0)
+
+#endif
+
 /*
  * NMI vs Tracing
  * --------------
@@ -110,18 +139,14 @@ void irq_exit_rcu(void);
 	do {							\
 		lockdep_off();					\
 		arch_nmi_enter();				\
-		/* Maximum NMI nesting is 15. */		\
-		BUG_ON(__this_cpu_read(nmi_nesting) >= 15);	\
-		__this_cpu_inc(nmi_nesting);			\
-		__preempt_count_add(HARDIRQ_OFFSET);		\
-		preempt_count_set(preempt_count() | NMI_MASK);	\
+		__preempt_count_nmi_enter();			\
 	} while (0)
 
 #define nmi_enter()						\
 	do {							\
 		__nmi_enter();					\
 		lockdep_hardirq_enter();			\
-		ct_nmi_enter();				\
+		ct_nmi_enter();					\
 		instrumentation_begin();			\
 		ftrace_nmi_enter();				\
 		instrumentation_end();				\
@@ -129,12 +154,8 @@ void irq_exit_rcu(void);
 
 #define __nmi_exit()						\
 	do {							\
-		unsigned int nesting;				\
 		BUG_ON(!in_nmi());				\
-		__preempt_count_sub(HARDIRQ_OFFSET);		\
-		nesting = __this_cpu_dec_return(nmi_nesting);	\
-		if (!nesting)					\
-			preempt_count_set(preempt_count() & ~NMI_MASK);	\
+		__preempt_count_nmi_exit();			\
 		arch_nmi_exit();				\
 		lockdep_on();					\
 	} while (0)
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 33fc4c814a9f..8299657f0f86 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -34,14 +34,31 @@
  *         SOFTIRQ_MASK:	0x0000ff00
  * HARDIRQ_DISABLE_MASK:	0x00ff0000
  *         HARDIRQ_MASK:	0x0f000000
+ *
+ * When HAS_SEPARATE_PREEMPT_RESCHED_BITS=y, PREEMPT_NEED_RESCHED is put in a
+ * separate word and that allows 64bit load-store architectures to 'set'
+ * PREEMPT_NEED_RESCHED without messing up the otherwise symmetric
+ * modifications used on preempt_count and still load the whole thing
+ * (single-copy) atomically, without having to resort to full atomic
+ * operations.
+ *
+ * Because of the above, NMI_MASK bits are different depending on
+ * HAS_SEPARATE_PREEMPT_RESCHED_BITS:
+ *
+ * - HAS_SEPARATE_PREEMPT_RESCHED_BITS=n:
+ *
  *             NMI_MASK:	0x10000000
  * PREEMPT_NEED_RESCHED:	0x80000000
+ *
+ * - HAS_SEPARATE_PREEMPT_RESCHED_BITS=y:
+ *             NMI_MASK:	0xf0000000
+ * (PREEMPT_NEED_RESCHED is in a different word)
  */
 #define PREEMPT_BITS	8
 #define SOFTIRQ_BITS	8
 #define HARDIRQ_DISABLE_BITS	8
 #define HARDIRQ_BITS	4
-#define NMI_BITS	1
+#define NMI_BITS	(1 + 3*IS_ENABLED(CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS))
 
 #define PREEMPT_SHIFT	0
 #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
@@ -116,8 +133,8 @@ static __always_inline unsigned char interrupt_context_level(void)
  * preempt_count() is commonly implemented with READ_ONCE().
  */
 
-#define nmi_count()	(preempt_count() & NMI_MASK)
-#define hardirq_count()	(preempt_count() & HARDIRQ_MASK)
+#define nmi_count()		(preempt_count() & NMI_MASK)
+#define hardirq_count()		(preempt_count() & HARDIRQ_MASK)
 #ifdef CONFIG_PREEMPT_RT
 # define softirq_count()	(current->softirq_disable_cnt & SOFTIRQ_MASK)
 # define irq_count()		((preempt_count() & (NMI_MASK | HARDIRQ_MASK)) | softirq_count())
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 88c594c6d7fc..35f546a042b1 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -122,6 +122,10 @@ config PREEMPT_RT_NEEDS_BH_LOCK
 config PREEMPT_COUNT
        bool
 
+config HAS_SEPARATE_PREEMPT_RESCHED_BITS
+	bool
+	depends on PREEMPT_COUNT && 64BIT
+
 config PREEMPTION
        bool
        select PREEMPT_COUNT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9b3f1764fa9e..6d88343c3bad 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5973,8 +5973,13 @@ void preempt_count_add(int val)
 #ifdef CONFIG_DEBUG_PREEMPT
 	/*
 	 * Underflow?
+	 *
+	 * Cannot detect underflow based on the current preempt_count() value
+	 * if using HAS_SEPARATE_PREEMPT_RESCHED_BITS because preempt count takes all 32
+	 * bits.
 	 */
-	if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
+	if (!IS_ENABLED(CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS) &&
+	    DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
 		return;
 #endif
 	__preempt_count_add(val);
@@ -6006,7 +6011,10 @@ void preempt_count_sub(int val)
 	/*
 	 * Underflow?
 	 */
-	if (DEBUG_LOCKS_WARN_ON(val > preempt_count()))
+	unsigned int uval = val;
+	unsigned int pc = preempt_count();
+
+	if (DEBUG_LOCKS_WARN_ON(pc - uval > pc))
 		return;
 	/*
 	 * Is the spinlock portion underflowing?
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 0c9b2269a8d6..7980a4a232f9 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -103,7 +103,13 @@ void _local_interrupt_enable(void)
 }
 EXPORT_SYMBOL(_local_interrupt_enable);
 
+#ifndef CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS
+/*
+ * Any 32bit architecture that still cares about performance should
+ * probably ensure this is near preempt_count.
+ */
 DEFINE_PER_CPU(unsigned int, nmi_nesting);
+#endif
 
 /*
  * SOFTIRQ_OFFSET usage:
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 0159a3d365c8..56520d551abd 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -368,7 +368,7 @@ extern int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str,
 #define SOFTIRQ_BITS	8
 #define HARDIRQ_DISABLE_BITS	8
 #define HARDIRQ_BITS	4
-#define NMI_BITS	1
+#define NMI_BITS	(1 + 3*IS_ENABLED(CONFIG_HAS_SEPARATE_PREEMPT_RESCHED_BITS))
 
 #define PREEMPT_SHIFT	0
 #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
-- 
2.50.1 (Apple Git-155)

[PATCH v5 12/18] arm64: sched/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS

[Boqun Feng]

Arm64 already uses 64-bit preempt count and the need reschedule bit is
maintained in a separate 32-bit word from the preempt count. Therefore
preempt count has enough bits to represent 16 levels of NMI nesting,
hence enable it for arm64. This saves a per-CPU variable and additional
instructions in the NMI path.

Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 arch/arm64/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b3afe0688919..349c3533cd1e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -247,6 +247,7 @@ config ARM64
 	select PCI_SYSCALL if PCI
 	select POWER_RESET
 	select POWER_SUPPLY
+	select HAS_SEPARATE_PREEMPT_RESCHED_BITS
 	select SPARSE_IRQ
 	select SWIOTLB
 	select SYSCTL_EXCEPTION_TRACE
-- 
2.50.1 (Apple Git-155)

[PATCH v5 13/18] s390/preempt: Enable HAS_SEPARATE_PREEMPT_RESCHED_BITS

[Boqun Feng]

From: Heiko Carstens <hca@linux.ibm.com>

Convert s390's preempt_count to 64 bit, and change the preempt
primitives accordingly.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
[boqun: Apply the corrected comment for asm block]
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 arch/s390/Kconfig               |  1 +
 arch/s390/include/asm/lowcore.h | 13 +++++++---
 arch/s390/include/asm/preempt.h | 43 +++++++++++++++------------------
 3 files changed, 30 insertions(+), 27 deletions(-)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 84404e6778d5..378fcd2b6181 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -273,6 +273,7 @@ config S390
 	select PCI_MSI			if PCI
 	select PCI_MSI_ARCH_FALLBACKS	if PCI_MSI
 	select PCI_QUIRKS		if PCI
+	select HAS_SEPARATE_PREEMPT_RESCHED_BITS
 	select SPARSE_IRQ
 	select SWIOTLB
 	select SYSCTL_EXCEPTION_TRACE
diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index 3b3ecc647993..5cef215d30e7 100644
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -160,10 +160,15 @@ struct lowcore {
 	/* SMP info area */
 	__u32	cpu_nr;				/* 0x03a0 */
 	__u32	softirq_pending;		/* 0x03a4 */
-	__s32	preempt_count;			/* 0x03a8 */
-	__u32	spinlock_lockval;		/* 0x03ac */
-	__u32	spinlock_index;			/* 0x03b0 */
-	__u8	pad_0x03b4[0x03b8-0x03b4];	/* 0x03b4 */
+	union {
+		struct {
+			__u32	need_resched;	/* 0x03a8 */
+			__u32	count;		/* 0x03ac */
+		} preempt;
+		__u64	preempt_count;		/* 0x03a8 */
+	};
+	__u32	spinlock_lockval;		/* 0x03b0 */
+	__u32	spinlock_index;			/* 0x03b4 */
 	__u64	percpu_offset;			/* 0x03b8 */
 	__u8	percpu_register;		/* 0x03c0 */
 	__u8	pad_0x03c1[0x0400-0x03c1];	/* 0x03c1 */
diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h
index 0a25d4648b4c..5560d5fca2a3 100644
--- a/arch/s390/include/asm/preempt.h
+++ b/arch/s390/include/asm/preempt.h
@@ -8,11 +8,8 @@
 #include <asm/cmpxchg.h>
 #include <asm/march.h>
 
-/*
- * Use MSB so it is possible to read preempt_count with LLGT which
- * reads the least significant 31 bits with a single instruction.
- */
-#define PREEMPT_NEED_RESCHED	0x80000000
+/* Use MSB for PREEMPT_NEED_RESCHED mostly because it is available. */
+#define PREEMPT_NEED_RESCHED	0x8000000000000000UL
 
 /*
  * We use the PREEMPT_NEED_RESCHED bit as an inverted NEED_RESCHED such
@@ -26,25 +23,25 @@
  */
 static __always_inline int preempt_count(void)
 {
-	unsigned long lc_preempt, count;
+	unsigned long lc_preempt;
+	int count;
 
-	BUILD_BUG_ON(sizeof_field(struct lowcore, preempt_count) != sizeof(int));
-	lc_preempt = offsetof(struct lowcore, preempt_count);
-	/* READ_ONCE(get_lowcore()->preempt_count) & ~PREEMPT_NEED_RESCHED */
+	lc_preempt = offsetof(struct lowcore, preempt.count);
+	/* READ_ONCE(get_lowcore()->preempt.count) (without PREEMPT_NEED_RESCHED) */
 	asm_inline(
-		ALTERNATIVE("llgt	%[count],%[offzero](%%r0)\n",
-			    "llgt	%[count],%[offalt](%%r0)\n",
+		ALTERNATIVE("ly		%[count],%[offzero](%%r0)\n",
+			    "ly		%[count],%[offalt](%%r0)\n",
 			    ALT_FEATURE(MFEATURE_LOWCORE))
 		: [count] "=d" (count)
 		: [offzero] "i" (lc_preempt),
 		  [offalt] "i" (lc_preempt + LOWCORE_ALT_ADDRESS),
-		  "m" (((struct lowcore *)0)->preempt_count));
+		  "m" (((struct lowcore *)0)->preempt.count));
 	return count;
 }
 
-static __always_inline void preempt_count_set(int pc)
+static __always_inline void preempt_count_set(unsigned long pc)
 {
-	int old, new;
+	unsigned long old, new;
 
 	old = READ_ONCE(get_lowcore()->preempt_count);
 	do {
@@ -63,12 +60,12 @@ static __always_inline void preempt_count_set(int pc)
 
 static __always_inline void set_preempt_need_resched(void)
 {
-	__atomic_and(~PREEMPT_NEED_RESCHED, &get_lowcore()->preempt_count);
+	__atomic64_and(~PREEMPT_NEED_RESCHED, (long *)&get_lowcore()->preempt_count);
 }
 
 static __always_inline void clear_preempt_need_resched(void)
 {
-	__atomic_or(PREEMPT_NEED_RESCHED, &get_lowcore()->preempt_count);
+	__atomic64_or(PREEMPT_NEED_RESCHED, (long *)&get_lowcore()->preempt_count);
 }
 
 static __always_inline bool test_preempt_need_resched(void)
@@ -88,8 +85,8 @@ static __always_inline void __preempt_count_add(int val)
 
 			lc_preempt = offsetof(struct lowcore, preempt_count);
 			asm_inline(
-				ALTERNATIVE("asi	%[offzero](%%r0),%[val]\n",
-					    "asi	%[offalt](%%r0),%[val]\n",
+				ALTERNATIVE("agsi	%[offzero](%%r0),%[val]\n",
+					    "agsi	%[offalt](%%r0),%[val]\n",
 					    ALT_FEATURE(MFEATURE_LOWCORE))
 				: "+m" (((struct lowcore *)0)->preempt_count)
 				: [offzero] "i" (lc_preempt), [val] "i" (val),
@@ -98,7 +95,7 @@ static __always_inline void __preempt_count_add(int val)
 			return;
 		}
 	}
-	__atomic_add(val, &get_lowcore()->preempt_count);
+	__atomic64_add(val, (long *)&get_lowcore()->preempt_count);
 }
 
 static __always_inline void __preempt_count_sub(int val)
@@ -119,15 +116,15 @@ static __always_inline bool __preempt_count_dec_and_test(void)
 
 	lc_preempt = offsetof(struct lowcore, preempt_count);
 	asm_inline(
-		ALTERNATIVE("alsi	%[offzero](%%r0),%[val]\n",
-			    "alsi	%[offalt](%%r0),%[val]\n",
+		ALTERNATIVE("algsi	%[offzero](%%r0),%[val]\n",
+			    "algsi	%[offalt](%%r0),%[val]\n",
 			    ALT_FEATURE(MFEATURE_LOWCORE))
 		: "=@cc" (cc), "+m" (((struct lowcore *)0)->preempt_count)
 		: [offzero] "i" (lc_preempt), [val] "i" (-1),
 		[offalt] "i" (lc_preempt + LOWCORE_ALT_ADDRESS));
 	return (cc == 0) || (cc == 2);
 #else
-	return __atomic_add_const_and_test(-1, &get_lowcore()->preempt_count);
+	return __atomic64_add_const_and_test(-1, (long *)&get_lowcore()->preempt_count);
 #endif
 }
 
@@ -141,7 +138,7 @@ static __always_inline bool should_resched(int preempt_offset)
 
 static __always_inline int __preempt_count_add_return(int val)
 {
-	return val + __atomic_add(val, &get_lowcore()->preempt_count);
+	return val + __atomic64_add(val, (long *)&get_lowcore()->preempt_count);
 }
 
 static __always_inline int __preempt_count_sub_return(int val)
-- 
2.50.1 (Apple Git-155)

[PATCH v5 14/18] rust: Introduce interrupt module

[Boqun Feng]

From: Lyude Paul <lyude@redhat.com>

This introduces a module for dealing with interrupt-disabled contexts,
including the ability to enable and disable interrupts along with the
ability to annotate functions as expecting that IRQs are already
disabled on the local CPU.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 rust/helpers/helpers.c   |  1 +
 rust/helpers/interrupt.c | 18 ++++++++
 rust/helpers/sync.c      |  5 +++
 rust/kernel/interrupt.rs | 89 ++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs       |  1 +
 5 files changed, 114 insertions(+)
 create mode 100644 rust/helpers/interrupt.c
 create mode 100644 rust/kernel/interrupt.rs

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 998e31052e66..0d85b5e68ec2 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -65,6 +65,7 @@
 #include "irq.c"
 #include "fs.c"
 #include "gpu.c"
+#include "interrupt.c"
 #include "io.c"
 #include "jump_label.c"
 #include "kunit.c"
diff --git a/rust/helpers/interrupt.c b/rust/helpers/interrupt.c
new file mode 100644
index 000000000000..51b319bd4c00
--- /dev/null
+++ b/rust/helpers/interrupt.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/spinlock.h>
+
+__rust_helper void rust_helper_local_interrupt_disable(void)
+{
+	local_interrupt_disable();
+}
+
+__rust_helper void rust_helper_local_interrupt_enable(void)
+{
+	local_interrupt_enable();
+}
+
+__rust_helper bool rust_helper_irqs_disabled(void)
+{
+	return irqs_disabled();
+}
diff --git a/rust/helpers/sync.c b/rust/helpers/sync.c
index 82d6aff73b04..4f474fe847c4 100644
--- a/rust/helpers/sync.c
+++ b/rust/helpers/sync.c
@@ -11,3 +11,8 @@ __rust_helper void rust_helper_lockdep_unregister_key(struct lock_class_key *k)
 {
 	lockdep_unregister_key(k);
 }
+
+__rust_helper void rust_helper_lockdep_assert_irqs_disabled(void)
+{
+	lockdep_assert_irqs_disabled();
+}
diff --git a/rust/kernel/interrupt.rs b/rust/kernel/interrupt.rs
new file mode 100644
index 000000000000..a880ec3b8538
--- /dev/null
+++ b/rust/kernel/interrupt.rs
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Interrupt controls
+//!
+//! This module allows Rust code to annotate areas of code where local processor interrupts should
+//! be disabled, along with actually disabling local processor interrupts.
+//!
+//! # ⚠️ Warning! ⚠️
+//!
+//! The usage of this module can be more complicated than meets the eye, especially surrounding
+//! [preemptible kernels]. It's recommended to take care when using the functions and types defined
+//! here and familiarize yourself with the various documentation we have before using them, along
+//! with the various documents we link to here.
+//!
+//! # Reading material
+//!
+//! - [Software interrupts and realtime (LWN)](https://lwn.net/Articles/520076)
+//!
+//! [preemptible kernels]: https://www.kernel.org/doc/html/latest/locking/preempt-locking.html
+
+use crate::types::NotThreadSafe;
+
+/// A guard that represents local processor interrupt disablement on preemptible kernels.
+///
+/// [`LocalInterruptDisabled`] is a guard type that represents that local processor interrupts have
+/// been disabled on a preemptible kernel.
+///
+/// Certain functions take an immutable reference of [`LocalInterruptDisabled`] in order to require
+/// that they may only be run in local-interrupt-disabled contexts on preemptible kernels.
+///
+/// This is a marker type; it has no size, and is simply used as a compile-time guarantee that local
+/// processor interrupts are disabled on preemptible kernels. Note that no guarantees about the
+/// state of interrupts are made by this type on non-preemptible kernels.
+///
+/// # Invariants
+///
+/// Local processor interrupts are disabled on preemptible kernels for as long as an object of this
+/// type exists.
+pub struct LocalInterruptDisabled(NotThreadSafe);
+
+/// Disable local processor interrupts on a preemptible kernel.
+///
+/// This function disables local processor interrupts on a preemptible kernel, and returns a
+/// [`LocalInterruptDisabled`] token as proof of this. On non-preemptible kernels, this function is
+/// a no-op.
+///
+/// **Usage of this function is discouraged** unless you are absolutely sure you know what you are
+/// doing, as kernel interfaces for Rust that deal with interrupt state will typically handle local
+/// processor interrupt state management on their own and managing this by hand is quite error
+/// prone.
+#[inline]
+pub fn local_interrupt_disable() -> LocalInterruptDisabled {
+    // SAFETY: It's always safe to call `local_interrupt_disable()`.
+    unsafe { bindings::local_interrupt_disable() };
+
+    LocalInterruptDisabled(NotThreadSafe)
+}
+
+impl Drop for LocalInterruptDisabled {
+    #[inline]
+    fn drop(&mut self) {
+        // SAFETY: Per type invariants, a `local_interrupt_disable()` must be called to create this
+        // object, hence calling the corresponding `local_interrupt_enable()` is safe.
+        unsafe { bindings::local_interrupt_enable() };
+    }
+}
+
+impl LocalInterruptDisabled {
+    /// Assume that local processor interrupts are disabled on preemptible kernels.
+    ///
+    /// This can be used for annotating code that is known to be run in contexts where local
+    /// processor interrupts are disabled on preemptible kernels. It makes no changes to the local
+    /// interrupt state on its own.
+    ///
+    /// # Safety
+    ///
+    /// For the whole life `'a`, local interrupts must be disabled on preemptible kernels. This
+    /// could be a context like, for example, an interrupt handler.
+    #[inline]
+    pub unsafe fn assume_disabled<'a>() -> &'a LocalInterruptDisabled {
+        const ASSUME_DISABLED: &LocalInterruptDisabled = &LocalInterruptDisabled(NotThreadSafe);
+
+        // Confirm they're actually disabled if lockdep is available
+        // SAFETY: It's always safe to call `lockdep_assert_irqs_disabled()`.
+        unsafe { bindings::lockdep_assert_irqs_disabled() };
+
+        ASSUME_DISABLED
+    }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 9512af7156df..2ee6c24d39c2 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -82,6 +82,7 @@
 pub mod impl_flags;
 pub mod init;
 pub mod interop;
+pub mod interrupt;
 pub mod io;
 pub mod ioctl;
 pub mod iommu;
-- 
2.50.1 (Apple Git-155)

[PATCH v5 15/18] rust: helper: Add spin_{un,}lock_irq_{enable,disable}() helpers

[Boqun Feng]

spin_lock_irq_disable() and spin_unlock_irq_enable() are inline
functions, to use them in Rust helpers are introduced. This is for
interrupt disabling lock abstraction in Rust.

Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 rust/helpers/spinlock.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/rust/helpers/spinlock.c b/rust/helpers/spinlock.c
index 4d13062cf253..d53400c15022 100644
--- a/rust/helpers/spinlock.c
+++ b/rust/helpers/spinlock.c
@@ -36,3 +36,18 @@ __rust_helper void rust_helper_spin_assert_is_held(spinlock_t *lock)
 {
 	lockdep_assert_held(lock);
 }
+
+__rust_helper void rust_helper_spin_lock_irq_disable(spinlock_t *lock)
+{
+	spin_lock_irq_disable(lock);
+}
+
+__rust_helper void rust_helper_spin_unlock_irq_enable(spinlock_t *lock)
+{
+	spin_unlock_irq_enable(lock);
+}
+
+__rust_helper int rust_helper_spin_trylock_irq_disable(spinlock_t *lock)
+{
+	return spin_trylock_irq_disable(lock);
+}
-- 
2.50.1 (Apple Git-155)

[PATCH v5 16/18] rust: sync: Use super::* in spinlock.rs

[Boqun Feng]

From: Lyude Paul <lyude@redhat.com>

No functional changes.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 rust/kernel/sync/lock/spinlock.rs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index ef76fa07ca3a..d75af32218ba 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -3,6 +3,7 @@
 //! A kernel spinlock.
 //!
 //! This module allows Rust code to use the kernel's `spinlock_t`.
+use super::*;
 
 /// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
 ///
@@ -82,7 +83,7 @@ macro_rules! new_spinlock {
 /// ```
 ///
 /// [`spinlock_t`]: srctree/include/linux/spinlock.h
-pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
+pub type SpinLock<T> = Lock<T, SpinLockBackend>;
 
 /// A kernel `spinlock_t` lock backend.
 pub struct SpinLockBackend;
@@ -91,13 +92,11 @@ macro_rules! new_spinlock {
 ///
 /// This is simply a type alias for a [`Guard`] returned from locking a [`SpinLock`]. It will unlock
 /// the [`SpinLock`] upon being dropped.
-///
-/// [`Guard`]: super::Guard
-pub type SpinLockGuard<'a, T> = super::Guard<'a, T, SpinLockBackend>;
+pub type SpinLockGuard<'a, T> = Guard<'a, T, SpinLockBackend>;
 
 // SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
 // default implementation that always calls the same locking method.
-unsafe impl super::Backend for SpinLockBackend {
+unsafe impl Backend for SpinLockBackend {
     type State = bindings::spinlock_t;
     type GuardState = ();
 
-- 
2.50.1 (Apple Git-155)

[PATCH v5 17/18] rust: sync: Add SpinLockIrq

[Boqun Feng]

From: Lyude Paul <lyude@redhat.com>

A variant of `SpinLock` that ensures interrupts are disabled in the
critical section. `lock()` will ensure that either interrupts are
already disabled or disable them. `unlock()` will reverse the respective
operation.

[Boqun: Port to use spin_lock_irq_disable() and
spin_unlock_irq_enable()]

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 rust/kernel/sync.rs               |   9 +-
 rust/kernel/sync/lock/global.rs   |   3 +
 rust/kernel/sync/lock/spinlock.rs | 230 ++++++++++++++++++++++++++++++
 3 files changed, 241 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index 993dbf2caa0e..df4f2604ff9b 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -27,7 +27,14 @@
 pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult};
 pub use lock::global::{global_lock, GlobalGuard, GlobalLock, GlobalLockBackend, GlobalLockedBy};
 pub use lock::mutex::{new_mutex, Mutex, MutexGuard};
-pub use lock::spinlock::{new_spinlock, SpinLock, SpinLockGuard};
+pub use lock::spinlock::{
+    new_spinlock,
+    new_spinlock_irq,
+    SpinLock,
+    SpinLockGuard,
+    SpinLockIrq,
+    SpinLockIrqGuard, //
+};
 pub use locked_by::LockedBy;
 pub use refcount::Refcount;
 pub use set_once::SetOnce;
diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
index ec2dd84316fc..ebb10521d8bd 100644
--- a/rust/kernel/sync/lock/global.rs
+++ b/rust/kernel/sync/lock/global.rs
@@ -306,4 +306,7 @@ macro_rules! global_lock_inner {
     (backend SpinLock) => {
         $crate::sync::lock::spinlock::SpinLockBackend
     };
+    (backend SpinLockIrq) => {
+        $crate::sync::lock::spinlock::SpinLockIrqBackend
+    };
 }
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index d75af32218ba..872544948e5d 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -4,6 +4,7 @@
 //!
 //! This module allows Rust code to use the kernel's `spinlock_t`.
 use super::*;
+use crate::prelude::*;
 
 /// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
 ///
@@ -143,3 +144,232 @@ unsafe fn assert_is_held(ptr: *mut Self::State) {
         unsafe { bindings::spin_assert_is_held(ptr) }
     }
 }
+
+/// Creates a [`SpinLockIrq`] initialiser with the given name and a newly-created lock class.
+///
+/// It uses the name if one is given, otherwise it generates one based on the file name and line
+/// number.
+#[macro_export]
+macro_rules! new_spinlock_irq {
+    ($inner:expr $(, $name:literal)? $(,)?) => {
+        $crate::sync::SpinLockIrq::new(
+            $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
+    };
+}
+pub use new_spinlock_irq;
+
+/// A variant of `SpinLock` that ensures interrupts are disabled in the critical section.
+///
+/// For more info on spinlocks, see [`SpinLock`]. For more information on interrupts,
+/// [see the interrupt module](kernel::interrupt).
+///
+/// # Examples
+///
+/// The following example shows how to declare, allocate initialise and access a struct (`Example`)
+/// that contains an inner struct (`Inner`) that is protected by a spinlock that requires local
+/// processor interrupts to be disabled.
+///
+/// ```
+/// use kernel::sync::{new_spinlock_irq, SpinLockIrq};
+///
+/// struct Inner {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// #[pin_data]
+/// struct Example {
+///     #[pin]
+///     c: SpinLockIrq<Inner>,
+///     #[pin]
+///     d: SpinLockIrq<Inner>,
+/// }
+///
+/// impl Example {
+///     fn new() -> impl PinInit<Self> {
+///         pin_init!(Self {
+///             c <- new_spinlock_irq!(Inner { a: 0, b: 10 }),
+///             d <- new_spinlock_irq!(Inner { a: 20, b: 30 }),
+///         })
+///     }
+/// }
+///
+/// // Allocate a boxed `Example`
+/// let e = KBox::pin_init(Example::new(), GFP_KERNEL)?;
+///
+/// // Accessing an `Example` from a context where interrupts may not be disabled already.
+/// let c_guard = e.c.lock(); // interrupts are disabled now, +1 interrupt disable refcount
+/// let d_guard = e.d.lock(); // no interrupt state change, +1 interrupt disable refcount
+///
+/// assert_eq!(c_guard.a, 0);
+/// assert_eq!(c_guard.b, 10);
+/// assert_eq!(d_guard.a, 20);
+/// assert_eq!(d_guard.b, 30);
+///
+/// drop(c_guard); // Dropping c_guard will not re-enable interrupts just yet, since d_guard is
+///                // still in scope.
+/// drop(d_guard); // Last interrupt disable reference dropped here, so interrupts are re-enabled
+///                // now
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// [`lock()`]: SpinLockIrq::lock
+pub type SpinLockIrq<T> = super::Lock<T, SpinLockIrqBackend>;
+
+/// A kernel `spinlock_t` lock backend that can only be acquired in interrupt disabled contexts.
+pub struct SpinLockIrqBackend;
+
+/// A [`Guard`] acquired from locking a [`SpinLockIrq`] using [`lock()`].
+///
+/// This is simply a type alias for a [`Guard`] returned from locking a [`SpinLockIrq`] using
+/// [`lock()`]. It will unlock the [`SpinLockIrq`] and decrement the local processor's interrupt
+/// disablement refcount upon being dropped.
+///
+/// [`lock()`]: SpinLockIrq::lock
+pub type SpinLockIrqGuard<'a, T> = Guard<'a, T, SpinLockIrqBackend>;
+
+// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
+// default implementation that always calls the same locking method.
+unsafe impl Backend for SpinLockIrqBackend {
+    type State = bindings::spinlock_t;
+    type GuardState = ();
+
+    #[inline]
+    unsafe fn init(
+        ptr: *mut Self::State,
+        name: *const crate::ffi::c_char,
+        key: *mut bindings::lock_class_key,
+    ) {
+        // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
+        // `key` are valid for read indefinitely.
+        unsafe { bindings::__spin_lock_init(ptr, name, key) }
+    }
+
+    #[inline]
+    unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
+        // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
+        // memory, and that it has been initialised before.
+        unsafe { bindings::spin_lock_irq_disable(ptr) }
+    }
+
+    #[inline]
+    unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
+        // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
+        // caller is the owner of the spinlock.
+        unsafe { bindings::spin_unlock_irq_enable(ptr) }
+    }
+
+    #[inline]
+    unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
+        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+        let result = unsafe { bindings::spin_trylock_irq_disable(ptr) };
+
+        if result != 0 {
+            Some(())
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    unsafe fn assert_is_held(ptr: *mut Self::State) {
+        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+        unsafe { bindings::spin_assert_is_held(ptr) }
+    }
+}
+
+#[kunit_tests(rust_spinlock_irq_condvar)]
+mod tests {
+    use super::*;
+    use crate::{
+        sync::*,
+        workqueue::{
+            self,
+            impl_has_work,
+            new_work,
+            Work,
+            WorkItem, //
+        },
+    };
+
+    struct TestState {
+        value: u32,
+        waiter_ready: bool,
+    }
+
+    #[pin_data]
+    struct Test {
+        #[pin]
+        state: SpinLockIrq<TestState>,
+
+        #[pin]
+        state_changed: CondVar,
+
+        #[pin]
+        waiter_state_changed: CondVar,
+
+        #[pin]
+        wait_work: Work<Self>,
+    }
+
+    impl_has_work! {
+        impl HasWork<Self> for Test { self.wait_work }
+    }
+
+    impl Test {
+        pub(crate) fn new() -> Result<Arc<Self>> {
+            Arc::try_pin_init(
+                try_pin_init!(
+                    Self {
+                        state <- new_spinlock_irq!(TestState {
+                            value: 1,
+                            waiter_ready: false
+                        }),
+                        state_changed <- new_condvar!(),
+                        waiter_state_changed <- new_condvar!(),
+                        wait_work <- new_work!("IrqCondvarTest::wait_work")
+                    }
+                ),
+                GFP_KERNEL,
+            )
+        }
+    }
+
+    impl WorkItem for Test {
+        type Pointer = Arc<Self>;
+
+        fn run(this: Arc<Self>) {
+            // Wait for the test to be ready to wait for us
+            let mut state = this.state.lock();
+
+            // Make sure the interrupts actually turned off
+            // SAFETY: It's always safe to call `lockdep_assert_irqs_disabled()`
+            unsafe { bindings::lockdep_assert_irqs_disabled() };
+
+            while !state.waiter_ready {
+                this.waiter_state_changed.wait(&mut state);
+            }
+
+            // Deliver the exciting value update our test has been waiting for
+            state.value += 1;
+            this.state_changed.notify_sync();
+        }
+    }
+
+    #[test]
+    fn spinlock_irq_condvar() -> Result {
+        let testdata = Test::new()?;
+
+        let _ = workqueue::system().enqueue(testdata.clone());
+
+        // Let the updater know when we're ready to wait
+        let mut state = testdata.state.lock();
+        state.waiter_ready = true;
+        testdata.waiter_state_changed.notify_sync();
+
+        // Wait for the exciting value update
+        testdata.state_changed.wait(&mut state);
+        assert_eq!(state.value, 2);
+        Ok(())
+    }
+}
-- 
2.50.1 (Apple Git-155)

[PATCH v5 18/18] rust: sync: Introduce SpinLockIrq::lock_with() and friends

[Boqun Feng]

From: Lyude Paul <lyude@redhat.com>

`SpinLockIrq` and `SpinLock` use the exact same underlying C structure,
with the only real difference being that the former uses the
irq_disable() and irq_enable() variants for locking/unlocking. These
variants can introduce some minor overhead in contexts where we already
know that local processor interrupts are disabled, and as such we want a
way to be able to skip modifying processor interrupt state in said
contexts in order to avoid some overhead - just like the current C API
allows us to do.

In order to do this, we add some special functions for SpinLockIrq:
lock_with() and try_lock_with(), which allow acquiring the lock without
changing the interrupt state - as long as the caller can provide a
LocalInterruptDisabled reference to prove that local processor
interrupts have been disabled.

In some hacked-together benchmarks we ran, most of the time this did
actually seem to lead to a noticeable difference in overhead:

  From an aarch64 VM running on a MacBook M4:
    lock() when irq is disabled, 100 times cost Delta { nanos: 500 }
    lock_with() when irq is disabled, 100 times cost Delta { nanos: 292 }
    lock() when irq is enabled, 100 times cost Delta { nanos: 834 }

    lock() when irq is disabled, 100 times cost Delta { nanos: 459 }
    lock_with() when irq is disabled, 100 times cost Delta { nanos: 291 }
    lock() when irq is enabled, 100 times cost Delta { nanos: 709 }

  From an x86_64 VM (qemu/kvm) running on a i7-13700H
    lock() when irq is disabled, 100 times cost Delta { nanos: 1002 }
    lock_with() when irq is disabled, 100 times cost Delta { nanos: 729 }
    lock() when irq is enabled, 100 times cost Delta { nanos: 1516 }

    lock() when irq is disabled, 100 times cost Delta { nanos: 754 }
    lock_with() when irq is disabled, 100 times cost Delta { nanos: 966 }
    lock() when irq is enabled, 100 times cost Delta { nanos: 1227 }

    (note that there were some runs on x86_64 where lock() on irq
    disabled vs. lock_with() on irq disabled had equivalent benchmarks,
    but it very much appeared to be a minority of test runs.)

While it's not clear how this affects real-world workloads yet, let's
add this for the time being so we can find out.

This makes it so that a `SpinLockIrq` will work like a `SpinLock` if
interrupts are disabled. So a function:

        (&'a SpinLockIrq, &'a LocalInterruptDisabled) -> Guard<'a, .., SpinLockBackend>

makes sense. Note that due to `Guard` and `LocalInterruptDisabled`
having the same lifetime, interrupts cannot be enabled while the Guard
exists.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Boqun Feng <boqun@kernel.org>
---
 rust/kernel/sync/lock/spinlock.rs | 92 ++++++++++++++++++++++++++++++-
 1 file changed, 91 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index 872544948e5d..aafc80125f59 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -4,7 +4,10 @@
 //!
 //! This module allows Rust code to use the kernel's `spinlock_t`.
 use super::*;
-use crate::prelude::*;
+use crate::{
+    interrupt::LocalInterruptDisabled,
+    prelude::*, //
+};
 
 /// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
 ///
@@ -160,6 +163,16 @@ macro_rules! new_spinlock_irq {
 
 /// A variant of `SpinLock` that ensures interrupts are disabled in the critical section.
 ///
+/// This lock can be acquired in two ways:
+///
+/// - Using [`lock()`] like any other type of lock, in which case the bindings will modify the
+///   interrupt state to ensure that local processor interrupts remain disabled for at least as
+///   long as the [`SpinLockIrqGuard`] exists.
+/// - Using [`lock_with()`] in contexts where a [`LocalInterruptDisabled`] token is present and
+///   local processor interrupts are already known to be disabled, in which case the local
+///   interrupt state will not be touched. This method should be preferred if a
+///   [`LocalInterruptDisabled`] token is present in the scope.
+///
 /// For more info on spinlocks, see [`SpinLock`]. For more information on interrupts,
 /// [see the interrupt module](kernel::interrupt).
 ///
@@ -213,7 +226,47 @@ macro_rules! new_spinlock_irq {
 /// # Ok::<(), Error>(())
 /// ```
 ///
+/// The next example demonstrates locking a [`SpinLockIrq`] using [`lock_with()`] in a function
+/// which can only be called when local processor interrupts are already disabled.
+///
+/// ```
+/// use kernel::sync::{new_spinlock_irq, SpinLockIrq};
+/// use kernel::interrupt::*;
+///
+/// struct Inner {
+///     a: u32,
+/// }
+///
+/// #[pin_data]
+/// struct Example {
+///     #[pin]
+///     inner: SpinLockIrq<Inner>,
+/// }
+///
+/// impl Example {
+///     fn new() -> impl PinInit<Self> {
+///         pin_init!(Self {
+///             inner <- new_spinlock_irq!(Inner { a: 20 }),
+///         })
+///     }
+/// }
+///
+/// // Accessing an `Example` from a function that can only be called in no-interrupt contexts.
+/// fn noirq_work(e: &Example, interrupt_disabled: &LocalInterruptDisabled) {
+///     // Because we know interrupts are disabled from interrupt_disable, we can skip toggling
+///     // interrupt state using lock_with() and the provided token
+///     assert_eq!(e.inner.lock_with(interrupt_disabled).a, 20);
+/// }
+///
+/// # let e = KBox::pin_init(Example::new(), GFP_KERNEL)?;
+/// # let interrupt_guard = local_interrupt_disable();
+/// # noirq_work(&e, &interrupt_guard);
+/// #
+/// # Ok::<(), Error>(())
+/// ```
+///
 /// [`lock()`]: SpinLockIrq::lock
+/// [`lock_with()`]: SpinLockIrq::lock_with
 pub type SpinLockIrq<T> = super::Lock<T, SpinLockIrqBackend>;
 
 /// A kernel `spinlock_t` lock backend that can only be acquired in interrupt disabled contexts.
@@ -278,6 +331,43 @@ unsafe fn assert_is_held(ptr: *mut Self::State) {
     }
 }
 
+impl<T: ?Sized> Lock<T, SpinLockIrqBackend> {
+    /// Casts the lock as a `Lock<T, SpinLockBackend>`.
+    #[inline]
+    fn as_lock_in_interrupt<'a>(&'a self, _context: &'a LocalInterruptDisabled) -> &'a SpinLock<T> {
+        // SAFETY:
+        // - `Lock<T, SpinLockBackend>` and `Lock<T, SpinLockIrqBackend>` both have identical data
+        //   layouts.
+        // - As long as local interrupts are disabled (which is proven to be true by _context), it
+        //   is safe to treat a lock with SpinLockIrqBackend as a SpinLockBackend lock.
+        unsafe { core::mem::transmute(self) }
+    }
+
+    /// Acquires the lock without modifying local interrupt state.
+    ///
+    /// This function should be used in place of the more expensive [`Lock::lock()`] function when
+    /// possible for [`SpinLockIrq`] locks.
+    #[inline]
+    pub fn lock_with<'a>(&'a self, context: &'a LocalInterruptDisabled) -> SpinLockGuard<'a, T> {
+        self.as_lock_in_interrupt(context).lock()
+    }
+
+    /// Tries to acquire the lock without modifying local interrupt state.
+    ///
+    /// This function should be used in place of the more expensive [`Lock::try_lock()`] function
+    /// when possible for [`SpinLockIrq`] locks.
+    ///
+    /// Returns a guard that can be used to access the data protected by the lock if successful.
+    #[must_use = "if unused, the lock will be immediately unlocked"]
+    #[inline]
+    pub fn try_lock_with<'a>(
+        &'a self,
+        context: &'a LocalInterruptDisabled,
+    ) -> Option<SpinLockGuard<'a, T>> {
+        self.as_lock_in_interrupt(context).try_lock()
+    }
+}
+
 #[kunit_tests(rust_spinlock_irq_condvar)]
 mod tests {
     use super::*;
-- 
2.50.1 (Apple Git-155)