Re: [PATCH] sched: fix BUG in preempt_notifier

Wanpeng Li Wed, 01 Jul 2015 00:42:08 -0700


On 7/1/15 2:33 PM, Lidong Chen wrote:

Signed-off-by: Lidong Chen <[email protected]>


Subject: sched,kvm: Fix KVM preempt_notifier usage

The preempt-notifier API needs to sleep with the addition of the
static_key, we do however need to hold off preemption while modifying
the preempt notifier list, otherwise a preemption could observe an
inconsistent list state.

There is no reason to have preemption disabled in the caller,
registering a preempt notifier is a purely task local affair.

Therefore move the preempt_disable into the functions and change the
callers to a preemptible context.

Cc: Gleb Natapov<[email protected]>
Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
Reported-and-Tested-by: Pontus Fuchs<[email protected]>
Signed-off-by: Peter Zijlstra (Intel)<[email protected]>


If this commit in tip tree fix your bug?

Regards,
Wanpeng Li

---
  kernel/sched/core.c | 25 ++++---------------------
  1 file changed, 4 insertions(+), 21 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b803e1b..4a5a964 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2318,15 +2318,12 @@ void wake_up_new_task(struct task_struct *p)

#ifdef CONFIG_PREEMPT_NOTIFIERS-static struct static_key preempt_notifier_key = STATIC_KEY_INIT_FALSE;

-
  /**
   * preempt_notifier_register - tell me when current is being preempted & 
rescheduled
   * @notifier: notifier struct to register
   */
  void preempt_notifier_register(struct preempt_notifier *notifier)
  {
-       static_key_slow_inc(&preempt_notifier_key);
        hlist_add_head(&notifier->link, &current->preempt_notifiers);
  }
  EXPORT_SYMBOL_GPL(preempt_notifier_register);
@@ -2340,11 +2337,10 @@ EXPORT_SYMBOL_GPL(preempt_notifier_register);
  void preempt_notifier_unregister(struct preempt_notifier *notifier)
  {
        hlist_del(&notifier->link);
-       static_key_slow_dec(&preempt_notifier_key);
  }
  EXPORT_SYMBOL_GPL(preempt_notifier_unregister);

-static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)

+static void fire_sched_in_preempt_notifiers(struct task_struct *curr)
  {
        struct preempt_notifier *notifier;

@@ -2352,14 +2348,9 @@ static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)

                notifier->ops->sched_in(notifier, raw_smp_processor_id());
  }

-static __always_inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)

-{
-       if (static_key_false(&preempt_notifier_key))
-               __fire_sched_in_preempt_notifiers(curr);
-}

static void

-__fire_sched_out_preempt_notifiers(struct task_struct *curr,
+fire_sched_out_preempt_notifiers(struct task_struct *curr,
                                   struct task_struct *next)
  {
        struct preempt_notifier *notifier;
@@ -2368,21 +2359,13 @@ __fire_sched_out_preempt_notifiers(struct task_struct 
*curr,
                notifier->ops->sched_out(notifier, next);
  }

-static __always_inline void

-fire_sched_out_preempt_notifiers(struct task_struct *curr,
-                                struct task_struct *next)
-{
-       if (static_key_false(&preempt_notifier_key))
-               __fire_sched_out_preempt_notifiers(curr, next);
-}
-
  #else /* !CONFIG_PREEMPT_NOTIFIERS */

-static inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)

+static void fire_sched_in_preempt_notifiers(struct task_struct *curr)
  {
  }

-static inline void

+static void
  fire_sched_out_preempt_notifiers(struct task_struct *curr,
                                 struct task_struct *next)
  {


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Re: [PATCH] sched: fix BUG in preempt_notifier

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