Messages in this thread | | | Date | Mon, 30 Nov 2015 17:47:37 -0800 | Subject | Re: [PATCH] sched: remove false-positive warning from wake_up_process() | From | Linus Torvalds <> |
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On Mon, Nov 30, 2015 at 5:34 PM, Sasha Levin <sasha.levin@oracle.com> wrote: > Futex can have a spurious wake up before we actually wake it up on our own, > which will trigger this warning if the task is still stopped.
Actually, I think it would presumably be the other way around: a spurious stale futex wakeup happens *after* the process has been woken up for some other reason and moved to stopped state.
(The "wake up and move to stopped state" could be for the same reason: a SIGSTOP signal).
So the setup is presumably something like this:
- on cpu1: futex code is about to go to sleep, adds itself to the futex hash chains, but then gets interrupted by a SIGSTOP
- in the meantime, on cpu2, the futex is changed, and the wakup code sees the process from cpu1 on the futex hash chains
- on cpu1, the process has now removed itself from the hash chains, and goes through the signal code that sets the state to STOPPED
- in the meantime, on cpu2, the futex code now gets around to waking things up, and sees that stopped state
Roughly.
Linus
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