From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Manfred Spraul <manfred@colorfullife.com>,
LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH 2/3] ipc/sem.c: handle spurious wakeups
Date: Wed, 12 Oct 2011 09:09:35 +0200 [thread overview]
Message-ID: <1318403375.3968.4.camel@twins> (raw)
In-Reply-To: <20111011145441.228e4c94.akpm@linux-foundation.org>
On Tue, 2011-10-11 at 14:54 -0700, Andrew Morton wrote:
> On Sat, 24 Sep 2011 19:37:11 +0200
> Manfred Spraul <manfred@colorfullife.com> wrote:
>
> > semtimedop() does not handle spurious wakeups, it returns -EINTR to user space.
> > Most other schedule() users would just loop and not return to user space.
> > The patch adds such a loop to semtimedop()
>
> What is a "spurious wakeup" and how can a process receive one?
Its a wakeup unrelated to the condition its waiting for. They shouldn't
happen (often) but all wait loops should deal with them. Sadly of course
most out of core wait loops don't :-(
> I'm wondering about the userspace-visible effects of this change, and
> any compatibility issues?
For this particular case it would be returning to userspace with -EINTR
without a signal having been raised what so ever. Not a big deal as
userspace it supposed to be able to deal with -EINTR and retry.
Also, these spurious wakeups hardly ever happen in the current kernel, I
only noticed it because I made them slightly more likely with a patch
currently on the back-burner until I figure out a sane way to audit all
1400+ schedule() and co. callsites.
next prev parent reply other threads:[~2011-10-12 7:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-24 17:37 [PATCH 2/3] ipc/sem.c: handle spurious wakeups Manfred Spraul
2011-10-11 21:54 ` Andrew Morton
2011-10-12 7:09 ` Peter Zijlstra [this message]
2011-10-13 18:51 ` Manfred Spraul
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=1318403375.3968.4.camel@twins \
--to=a.p.zijlstra@chello.nl \
--cc=akpm@linux-foundation.org \
--cc=efault@gmx.de \
--cc=linux-kernel@vger.kernel.org \
--cc=manfred@colorfullife.com \
--cc=tglx@linutronix.de \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.