From: Linus Torvalds <torvalds@linux-foundation.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org,
a.p.zijlstra@chello.nl, y-goto@jp.fujitsu.com,
akpm@linux-foundation.org, tglx@linutronix.de, mingo@elte.hu,
linux-tip-commits@vger.kernel.org
Subject: Re: [tip:sched/core] sched: Fix ancient race in do_exit()
Date: Sun, 29 Jan 2012 10:28:06 -0800 [thread overview]
Message-ID: <CA+55aFx4nJwxWab4x8pKM+NEHPx_3kHbwf3xzQOLEpaXMks-CA@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFz20=H0ZubZEAmEbv0gL8j3C5Kgt4m2+5MU63uVipZt0Q@mail.gmail.com>
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
next prev parent reply other threads:[~2012-01-29 18:28 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-22 0:42 [BUG] TASK_DEAD task is able to be woken up in special condition Yasunori Goto
2011-12-22 2:14 ` KOSAKI Motohiro
2011-12-22 8:22 ` Yasunori Goto
2011-12-22 20:02 ` KOSAKI Motohiro
2011-12-23 9:49 ` Peter Zijlstra
2011-12-23 15:41 ` Oleg Nesterov
2011-12-26 8:23 ` Yasunori Goto
2011-12-26 17:11 ` Oleg Nesterov
2011-12-27 6:48 ` Yasunori Goto
2012-01-06 10:22 ` Yasunori Goto
2012-01-06 11:01 ` Peter Zijlstra
2012-01-06 12:01 ` Yasunori Goto
2012-01-06 12:43 ` Peter Zijlstra
2012-01-06 14:12 ` Oleg Nesterov
2012-01-06 14:19 ` Oleg Nesterov
2012-01-07 1:31 ` Yasunori Goto
2012-01-16 11:51 ` Yasunori Goto
2012-01-16 13:38 ` Peter Zijlstra
2012-01-17 8:40 ` Yasunori Goto
2012-01-17 9:06 ` Ingo Molnar
2012-01-17 15:12 ` Oleg Nesterov
2012-01-18 9:42 ` Ingo Molnar
2012-01-18 14:20 ` Oleg Nesterov
2012-01-24 10:19 ` Peter Zijlstra
2012-01-24 10:55 ` Peter Zijlstra
2012-01-24 17:25 ` KOSAKI Motohiro
2012-01-25 15:45 ` Oleg Nesterov
2012-01-25 16:51 ` Peter Zijlstra
2012-01-25 17:43 ` Oleg Nesterov
2012-01-26 15:32 ` Peter Zijlstra
2012-01-26 16:26 ` Oleg Nesterov
2012-01-27 8:59 ` Peter Zijlstra
2012-01-24 10:11 ` Peter Zijlstra
2012-01-26 9:39 ` Ingo Molnar
2012-01-28 12:03 ` [tip:sched/core] sched: Fix ancient race in do_exit() tip-bot for Yasunori Goto
2012-01-28 21:12 ` Linus Torvalds
2012-01-29 16:07 ` Oleg Nesterov
2012-01-29 17:44 ` Linus Torvalds
2012-01-29 18:28 ` Linus Torvalds [this message]
2012-01-29 18:59 ` Oleg Nesterov
2012-01-30 16:27 ` Linus Torvalds
2012-01-06 13:48 ` [BUG] TASK_DEAD task is able to be woken up in special condition Oleg Nesterov
2011-12-28 21:07 ` KOSAKI Motohiro
2012-01-24 10:23 ` Peter Zijlstra
2012-01-24 18:01 ` KOSAKI Motohiro
2012-01-25 6:15 ` Mike Galbraith
2012-01-26 21:24 ` KOSAKI Motohiro
2012-01-25 10:10 ` Peter Zijlstra
2012-01-26 20:25 ` [tip:sched/urgent] sched: Fix rq->nr_uninterruptible update race tip-bot for Peter Zijlstra
2012-01-27 5:20 ` Rakib Mullick
2012-01-27 8:19 ` Peter Zijlstra
2012-01-27 14:11 ` Rakib Mullick
2012-01-26 21:21 ` [BUG] TASK_DEAD task is able to be woken up in special condition KOSAKI Motohiro
2012-01-27 8:21 ` Peter Zijlstra
2011-12-26 6:52 ` Yasunori Goto
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CA+55aFx4nJwxWab4x8pKM+NEHPx_3kHbwf3xzQOLEpaXMks-CA@mail.gmail.com \
--to=torvalds@linux-foundation.org \
--cc=a.p.zijlstra@chello.nl \
--cc=akpm@linux-foundation.org \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=mingo@redhat.com \
--cc=oleg@redhat.com \
--cc=tglx@linutronix.de \
--cc=y-goto@jp.fujitsu.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).