* [PATCH] sched: reset task's lockless wake-queues on fork()
@ 2015-12-21 17:17 Sebastian Andrzej Siewior
2016-01-06 18:48 ` [tip:sched/core] sched/core: Reset task' s " tip-bot for Sebastian Andrzej Siewior
0 siblings, 1 reply; 4+ messages in thread
From: Sebastian Andrzej Siewior @ 2015-12-21 17:17 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Davidlohr Bueso, Thomas Gleixner, Steven Rostedt, linux-kernel,
Ingo Molnar
In 7675104990ed ("sched: Implement lockless wake-queues") we gained
lockless wake-queues. -RT managed to lockup itself with those. There
could be multiple attempts for task X to enqueue it for a wakeup
_even_ if task X is already running.
The reason is that task X could be runnable but not yet on CPU. The the
task performing the wakeup did not leave the CPU it could performe
multiple wakeups.
With the proper timming task X could be running and enqueued for a
wakeup. If this happens while X is performing a fork() then its its
child will have a !NULL `wake_q` member copied.
This is not a problem as long as the child task does not participate in
lockless wakeups :)
Fixes: 7675104990ed ("sched: Implement lockless wake-queues")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/fork.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/fork.c b/kernel/fork.c
index b508f757c60b..46c1e8342ad8 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -393,6 +393,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
#endif
tsk->splice_pipe = NULL;
tsk->task_frag.page = NULL;
+ tsk->wake_q.next = NULL;
account_kernel_stack(ti, 1);
--
2.6.4
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [tip:sched/core] sched/core: Reset task' s lockless wake-queues on fork()
2015-12-21 17:17 [PATCH] sched: reset task's lockless wake-queues on fork() Sebastian Andrzej Siewior
@ 2016-01-06 18:48 ` tip-bot for Sebastian Andrzej Siewior
2016-01-08 9:41 ` Thomas Gleixner
0 siblings, 1 reply; 4+ messages in thread
From: tip-bot for Sebastian Andrzej Siewior @ 2016-01-06 18:48 UTC (permalink / raw)
To: linux-tip-commits
Cc: mingo, rostedt, linux-kernel, dbueso, bigeasy, peterz, tglx,
torvalds, hpa
Commit-ID: 093e5840ae76f1082633503964d035f40ed0216d
Gitweb: http://git.kernel.org/tip/093e5840ae76f1082633503964d035f40ed0216d
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Mon, 21 Dec 2015 18:17:10 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 6 Jan 2016 11:01:07 +0100
sched/core: Reset task's lockless wake-queues on fork()
In the following commit:
7675104990ed ("sched: Implement lockless wake-queues")
we gained lockless wake-queues.
The -RT kernel managed to lockup itself with those. There could be multiple
attempts for task X to enqueue it for a wakeup _even_ if task X is already
running.
The reason is that task X could be runnable but not yet on CPU. The the
task performing the wakeup did not leave the CPU it could performe
multiple wakeups.
With the proper timming task X could be running and enqueued for a
wakeup. If this happens while X is performing a fork() then its its
child will have a !NULL `wake_q` member copied.
This is not a problem as long as the child task does not participate in
lockless wakeups :)
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 7675104990ed ("sched: Implement lockless wake-queues")
Link: http://lkml.kernel.org/r/20151221171710.GA5499@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/fork.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/fork.c b/kernel/fork.c
index fce002e..1155eac 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -380,6 +380,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
#endif
tsk->splice_pipe = NULL;
tsk->task_frag.page = NULL;
+ tsk->wake_q.next = NULL;
account_kernel_stack(ti, 1);
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [tip:sched/core] sched/core: Reset task' s lockless wake-queues on fork()
2016-01-06 18:48 ` [tip:sched/core] sched/core: Reset task' s " tip-bot for Sebastian Andrzej Siewior
@ 2016-01-08 9:41 ` Thomas Gleixner
2016-01-09 19:25 ` Davidlohr Bueso
0 siblings, 1 reply; 4+ messages in thread
From: Thomas Gleixner @ 2016-01-08 9:41 UTC (permalink / raw)
To: bigeasy, peterz, linux-kernel, dbueso, rostedt, mingo, hpa, torvalds
Cc: linux-tip-commits
On Wed, 6 Jan 2016, tip-bot for Sebastian Andrzej Siewior wrote:
> Commit-ID: 093e5840ae76f1082633503964d035f40ed0216d
> Gitweb: http://git.kernel.org/tip/093e5840ae76f1082633503964d035f40ed0216d
> Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> AuthorDate: Mon, 21 Dec 2015 18:17:10 +0100
> Committer: Ingo Molnar <mingo@kernel.org>
> CommitDate: Wed, 6 Jan 2016 11:01:07 +0100
>
> sched/core: Reset task's lockless wake-queues on fork()
>
> In the following commit:
>
> 7675104990ed ("sched: Implement lockless wake-queues")
>
> we gained lockless wake-queues.
>
> The -RT kernel managed to lockup itself with those. There could be multiple
> attempts for task X to enqueue it for a wakeup _even_ if task X is already
> running.
>
> The reason is that task X could be runnable but not yet on CPU. The the
> task performing the wakeup did not leave the CPU it could performe
> multiple wakeups.
>
> With the proper timming task X could be running and enqueued for a
> wakeup. If this happens while X is performing a fork() then its its
> child will have a !NULL `wake_q` member copied.
>
> This is not a problem as long as the child task does not participate in
> lockless wakeups :)
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Davidlohr Bueso <dbueso@suse.de>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Fixes: 7675104990ed ("sched: Implement lockless wake-queues")
Shouldn't that go into stable?
Thanks,
tglx
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [tip:sched/core] sched/core: Reset task' s lockless wake-queues on fork()
2016-01-08 9:41 ` Thomas Gleixner
@ 2016-01-09 19:25 ` Davidlohr Bueso
0 siblings, 0 replies; 4+ messages in thread
From: Davidlohr Bueso @ 2016-01-09 19:25 UTC (permalink / raw)
To: Thomas Gleixner
Cc: bigeasy, peterz, linux-kernel, dbueso, rostedt, mingo, hpa,
torvalds, linux-tip-commits, stable
On Fri, 08 Jan 2016, Thomas Gleixner wrote:
>On Wed, 6 Jan 2016, tip-bot for Sebastian Andrzej Siewior wrote:
>
>> Commit-ID: 093e5840ae76f1082633503964d035f40ed0216d
>> Gitweb: http://git.kernel.org/tip/093e5840ae76f1082633503964d035f40ed0216d
>> Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> AuthorDate: Mon, 21 Dec 2015 18:17:10 +0100
>> Committer: Ingo Molnar <mingo@kernel.org>
>> CommitDate: Wed, 6 Jan 2016 11:01:07 +0100
>>
>> sched/core: Reset task's lockless wake-queues on fork()
>>
>> In the following commit:
>>
>> 7675104990ed ("sched: Implement lockless wake-queues")
>>
>> we gained lockless wake-queues.
>>
>> The -RT kernel managed to lockup itself with those. There could be multiple
>> attempts for task X to enqueue it for a wakeup _even_ if task X is already
>> running.
>>
>> The reason is that task X could be runnable but not yet on CPU. The the
>> task performing the wakeup did not leave the CPU it could performe
>> multiple wakeups.
>>
>> With the proper timming task X could be running and enqueued for a
>> wakeup. If this happens while X is performing a fork() then its its
>> child will have a !NULL `wake_q` member copied.
>>
>> This is not a problem as long as the child task does not participate in
>> lockless wakeups :)
It also makes sense in that a new task has no business inherinting whatever
pending wakeups the parent is involved in. It should get a fresh wake_q.
>>
>> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>> Cc: Davidlohr Bueso <dbueso@suse.de>
>> Cc: Linus Torvalds <torvalds@linux-foundation.org>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Fixes: 7675104990ed ("sched: Implement lockless wake-queues")
>
>Shouldn't that go into stable?
Yes, as of v4.2 afaict. Ccing.
Thanks,
Davidlohr
^ permalink raw reply [flat|nested] 4+ messages in thread
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2015-12-21 17:17 [PATCH] sched: reset task's lockless wake-queues on fork() Sebastian Andrzej Siewior
2016-01-06 18:48 ` [tip:sched/core] sched/core: Reset task' s " tip-bot for Sebastian Andrzej Siewior
2016-01-08 9:41 ` Thomas Gleixner
2016-01-09 19:25 ` Davidlohr Bueso
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