Commit 093e5840 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Ingo Molnar

sched/core: Reset task's lockless wake-queues on fork()

In the following commit:

  76751049 ("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: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarPeter 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: 76751049 ("sched: Implement lockless wake-queues")
Link: http://lkml.kernel.org/r/20151221171710.GA5499@linutronix.deSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent be958bdc
...@@ -380,6 +380,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig) ...@@ -380,6 +380,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
#endif #endif
tsk->splice_pipe = NULL; tsk->splice_pipe = NULL;
tsk->task_frag.page = NULL; tsk->task_frag.page = NULL;
tsk->wake_q.next = NULL;
account_kernel_stack(ti, 1); account_kernel_stack(ti, 1);
......
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