Re: [PATCH] sched: fix BUG in preempt_notifier

From: Wanpeng Li
Date: Wed Jul 01 2015 - 03:41:46 EST




On 7/1/15 2:33 PM, Lidong Chen wrote:
Signed-off-by: Lidong Chen <cfme_admin@xxxxxxx>

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<gleb@xxxxxxxxxx>
Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
Reported-and-Tested-by: Pontus Fuchs<pontus.fuchs@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel)<peterz@xxxxxxxxxxxxx>


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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