[PATCH] sched: fix BUG in preempt_notifier

[PATCH] sched: fix BUG in preempt_notifier

[Lidong Chen]

Signed-off-by: Lidong Chen <cfme_admin@163.com>
---
 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)
 {
-- 
2.1.0

Re:[PATCH] sched: fix BUG in preempt_notifier

[cfme_admin]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset=UTF-8, Size: 3076 bytes --]



more information about the bug is below:
https://bugzilla.kernel.org/show_bug.cgi?id=100701

the preempt_notifier_unregister function is run in_atomic context, but static_key_slow_dec function may cause sleep.


At 2015-07-01 14:33:30, "Lidong Chen" <cfme_admin@163.com> wrote:
>Signed-off-by: Lidong Chen <cfme_admin@163.com>
>---
> 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)
> {
>-- 
>2.1.0
>
ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

Re: [PATCH] sched: fix BUG in preempt_notifier

[Ingo Molnar]

* cfme_admin <cfme_admin@163.com> wrote:

> more information about the bug is below:
> https://bugzilla.kernel.org/show_bug.cgi?id=100701
> 
> the preempt_notifier_unregister function is run in_atomic context, but static_key_slow_dec function may cause sleep.

This bug should already be fixed by this pending commit:

   6efde1d3716b ("sched/preempt, kvm: Fix KVM preempt_notifier usage")

Attached below.

Thanks,

	Ingo

========================>
>From 6efde1d3716b7d055d3310bccba2df244cf430d7 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Thu, 25 Jun 2015 14:55:14 +0200
Subject: [PATCH] sched/preempt, 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.

Reported-and-Tested-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Pontus Fuchs <pontus.fuchs@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
Link: http://lkml.kernel.org/r/20150625125514.GA3644@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c | 11 +++++++++++
 virt/kvm/kvm_main.c |  5 +++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c86935a7f1f8..5bcf926e62a4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2138,7 +2138,12 @@ static struct static_key preempt_notifier_key = STATIC_KEY_INIT_FALSE;
 void preempt_notifier_register(struct preempt_notifier *notifier)
 {
 	static_key_slow_inc(&preempt_notifier_key);
+	/*
+	 * Avoid preemption while changing the preempt notifier list.
+	 */
+	preempt_disable();
 	hlist_add_head(&notifier->link, &current->preempt_notifiers);
+	preempt_enable();
 }
 EXPORT_SYMBOL_GPL(preempt_notifier_register);
 
@@ -2150,7 +2155,13 @@ EXPORT_SYMBOL_GPL(preempt_notifier_register);
  */
 void preempt_notifier_unregister(struct preempt_notifier *notifier)
 {
+	/*
+	 * Avoid preemption while changing the preempt notifier list.
+	 */
+	preempt_disable();
 	hlist_del(&notifier->link);
+	preempt_enable();
+
 	static_key_slow_dec(&preempt_notifier_key);
 }
 EXPORT_SYMBOL_GPL(preempt_notifier_unregister);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 90977418aeb6..d7aafa0458a0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -128,8 +128,9 @@ int vcpu_load(struct kvm_vcpu *vcpu)
 
 	if (mutex_lock_killable(&vcpu->mutex))
 		return -EINTR;
-	cpu = get_cpu();
 	preempt_notifier_register(&vcpu->preempt_notifier);
+
+	cpu = get_cpu();
 	kvm_arch_vcpu_load(vcpu, cpu);
 	put_cpu();
 	return 0;
@@ -139,8 +140,8 @@ void vcpu_put(struct kvm_vcpu *vcpu)
 {
 	preempt_disable();
 	kvm_arch_vcpu_put(vcpu);
-	preempt_notifier_unregister(&vcpu->preempt_notifier);
 	preempt_enable();
+	preempt_notifier_unregister(&vcpu->preempt_notifier);
 	mutex_unlock(&vcpu->mutex);
 }
 

Re: [PATCH] sched: fix BUG in preempt_notifier

[Wanpeng Li]

On 7/1/15 2:33 PM, Lidong Chen wrote:
> Signed-off-by: Lidong Chen <cfme_admin@163.com>

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@kernel.org>
Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
Reported-and-Tested-by: Pontus Fuchs<pontus.fuchs@gmail.com>
Signed-off-by: Peter Zijlstra (Intel)<peterz@infradead.org>


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)
>   {

Re:Re: [PATCH] sched: fix BUG in preempt_notifier

[cfme_admin]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset=UTF-8, Size: 3975 bytes --]

This is a better way to solve this bug.
Thanks. 

At 2015-07-01 15:41:28, "Wanpeng Li" <wanpeng.li@hotmail.com> wrote:
>
>
>On 7/1/15 2:33 PM, Lidong Chen wrote:
>> Signed-off-by: Lidong Chen <cfme_admin@163.com>
>
>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@kernel.org>
>Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers")
>Reported-and-Tested-by: Pontus Fuchs<pontus.fuchs@gmail.com>
>Signed-off-by: Peter Zijlstra (Intel)<peterz@infradead.org>
>
>
>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)
>>   {
>
ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥