[PATCH 19/21] context_tracking: Convert state to atomic_t

Frederic Weisbecker
2022-05-19T15:01:42Z

Context tracking's state and dynticks counter are going to be merged
in a single field so that both updates can happen atomically and at the
same time. Prepare for that with converting the state into an atomic_t.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao<liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
---
include/linux/context_tracking.h | 24 ++++------------
include/linux/context_tracking_state.h | 40 ++++++++++++++++++++++----
kernel/context_tracking.c | 15 ++++++----
3 files changed, 49 insertions(+), 30 deletions(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 1f568676bc1d..a8c1db0a3f65 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -56,7 +56,7 @@ static inline enum ctx_state exception_enter(void)
!context_tracking_enabled())
return 0;

- prev_ctx = this_cpu_read(context_tracking.state);
+ prev_ctx = __ct_state();
if (prev_ctx != CONTEXT_KERNEL)
ct_user_exit(prev_ctx);

@@ -86,33 +86,21 @@ static __always_inline void context_tracking_guest_exit(void)
__ct_user_exit(CONTEXT_GUEST);
}

-/**
- * ct_state() - return the current context tracking state if known
- *
- * Returns the current cpu's context tracking state if context tracking
- * is enabled. If context tracking is disabled, returns
- * CONTEXT_DISABLED. This should be used primarily for debugging.
- */
-static __always_inline enum ctx_state ct_state(void)
-{
- return context_tracking_enabled() ?
- this_cpu_read(context_tracking.state) : CONTEXT_DISABLED;
-}
+#define CT_WARN_ON(cond) WARN_ON(context_tracking_enabled() && (cond))
+
#else
static inline void user_enter(void) { }
static inline void user_exit(void) { }
static inline void user_enter_irqoff(void) { }
static inline void user_exit_irqoff(void) { }
-static inline enum ctx_state exception_enter(void) { return 0; }
+static inline int exception_enter(void) { return 0; }
static inline void exception_exit(enum ctx_state prev_ctx) { }
-static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }
+static inline int ct_state(void) { return -1; }
static __always_inline bool context_tracking_guest_enter(void) { return false; }
static inline void context_tracking_guest_exit(void) { }
-
+#define CT_WARN_ON(cond)
#endif /* !CONFIG_CONTEXT_TRACKING_USER */

-#define CT_WARN_ON(cond) WARN_ON(context_tracking_enabled() && (cond))
-
#ifdef CONFIG_CONTEXT_TRACKING_USER_FORCE
extern void context_tracking_init(void);
#else
diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index b99e9827cc08..1501df6d4cfa 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -9,6 +9,13 @@
/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */
#define DYNTICK_IRQ_NONIDLE ((LONG_MAX / 2) + 1)

+enum ctx_state {
+ CONTEXT_DISABLED = -1, /* returned by ct_state() if unknown */
+ CONTEXT_KERNEL = 0,
+ CONTEXT_USER,
+ CONTEXT_GUEST,
+};
+
struct context_tracking {
#ifdef CONFIG_CONTEXT_TRACKING_USER
/*
@@ -19,12 +26,7 @@ struct context_tracking {
*/
bool active;
int recursion;
- enum ctx_state {
- CONTEXT_DISABLED = -1, /* returned by ct_state() if unknown */
- CONTEXT_KERNEL = 0,
- CONTEXT_USER,
- CONTEXT_GUEST,
- } state;
+ atomic_t state;
#endif
#ifdef CONFIG_CONTEXT_TRACKING_IDLE
atomic_t dynticks; /* Even value for idle, else odd. */
@@ -96,6 +98,32 @@ static inline bool context_tracking_enabled_this_cpu(void)
return context_tracking_enabled() && __this_cpu_read(context_tracking.active);
}

+static __always_inline int __ct_state(void)
+{
+ return atomic_read(this_cpu_ptr(&context_tracking.state));
+}
+
+/**
+ * ct_state() - return the current context tracking state if known
+ *
+ * Returns the current cpu's context tracking state if context tracking
+ * is enabled. If context tracking is disabled, returns
+ * CONTEXT_DISABLED. This should be used primarily for debugging.
+ */
+static __always_inline int ct_state(void)
+{
+ int ret;
+
+ if (!context_tracking_enabled())
+ return CONTEXT_DISABLED;
+
+ preempt_disable();
+ ret = __ct_state();
+ preempt_enable();
+
+ return ret;
+}
+
#else
static inline bool context_tracking_enabled(void) { return false; }
static inline bool context_tracking_enabled_cpu(int cpu) { return false; }
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 6152313ea787..30a3d4c8c045 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -460,6 +460,7 @@ static __always_inline void context_tracking_recursion_exit(void)
*/
void noinstr __ct_user_enter(enum ctx_state state)
{
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);
lockdep_assert_irqs_disabled();

/* Kernel threads aren't supposed to go to userspace */
@@ -468,8 +469,8 @@ void noinstr __ct_user_enter(enum ctx_state state)
if (!context_tracking_recursion_enter())
return;

- if ( __this_cpu_read(context_tracking.state) != state) {
- if (__this_cpu_read(context_tracking.active)) {
+ if (__ct_state() != state) {
+ if (ct->active) {
/*
* At this stage, only low level arch entry code remains and
* then we'll run in userspace. We can assume there won't be
@@ -510,7 +511,7 @@ void noinstr __ct_user_enter(enum ctx_state state)
* OTOH we can spare the calls to vtime and RCU when context_tracking.active
* is false because we know that CPU is not tickless.
*/
- __this_cpu_write(context_tracking.state, state);
+ atomic_set(&ct->state, state);
}
context_tracking_recursion_exit();
}
@@ -571,11 +572,13 @@ NOKPROBE_SYMBOL(user_enter_callable);
*/
void noinstr __ct_user_exit(enum ctx_state state)
{
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);
+
if (!context_tracking_recursion_enter())
return;

- if (__this_cpu_read(context_tracking.state) == state) {
- if (__this_cpu_read(context_tracking.active)) {
+ if (__ct_state() == state) {
+ if (ct->active) {
/*
* Exit RCU idle mode while entering the kernel because it can
* run a RCU read side critical section anytime.
@@ -588,7 +591,7 @@ void noinstr __ct_user_exit(enum ctx_state state)
instrumentation_end();
}
}
- __this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
+ atomic_set(&ct->state, CONTEXT_KERNEL);
}
context_tracking_recursion_exit();
}
--
2.25.1