Messages in this thread |  | | | From | Linus Torvalds <> | | Date | Sun, 29 Jan 2012 10:28:06 -0800 | | Subject | Re: [tip:sched/core] sched: Fix ancient race in do_exit() |
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On Sun, Jan 29, 2012 at 9:44 AM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > So it may be completely and utterly broken for some subtle reason, but > I don't see what it would be. It seems to clean up and simplify the > logic, and remove all the bogus workarounds for the fact that we used > to do things stupidly. > > But maybe there's some reason for those "stupid" things. I just don't see it.
Hmm. Ok, so I see one reason for it. The silly extraneous "set task to TASK_UNINTERRUPTIBLE" shouldn't matter normally - even if there are spurious wakeups (say, disk IO while taking a page fault - not that I see why we'd be on any wait queues yet), we'll just schedule a bit more than we need in the extremely unlikely case that they hit us.
But for RT tasks with higher priorities, looping - even if we call schedule() all the time - can cause livelocks. Damn. So while I don't think the spurious wakeup is a big issue (I don't think it happens in practice), it could lead to problems.
I think we could possibly use the "flags" field to do that "are we just about to get woken up" logic, and set TASK_UNINTERRUPTIBLE in the loop - and just clear "flags" before doing the wakeup (the same way we used to clear "task"). Dunno. Ideas?
Linus
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