linux-kernel - Re: 3.14-rc2 XFS backtrace because irqs

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Message-ID: <20140213181013.GA15596@redhat.com>
Date:	Thu, 13 Feb 2014 19:10:13 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>,
	Dave Jones <davej@...hat.com>,
	Eric Sandeen <sandeen@...deen.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>, xfs@....sgi.com
Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled.

On 02/13, Linus Torvalds wrote:
>
> On Thu, Feb 13, 2014 at 9:40 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > And we should be careful with SIGQUEUE_PREALLOC, at least
> > collect_signal() should not do list_del_init()... Plus we need to
> > handle the SEND_SIG_FORCED-like case.
>
> I don't think the users need to care. They'd just call
> "sigqueue_free()" not knowing about our preallocations etc.

Yes, but we need to be careful to avoid the races with
release_posix_timer().

> That kind
> of detail should be confined to inside signal.c.

Yes, sure.

> But there really aren't that many users. There's a couple of
> "dequeue_signal_lock()" users, but they don't actually *want* the
> siginfo at all (they're kernel threads), so we can just make that
> function free the siginfo immediately (and get rid of the totally
> unnecessay kernel stack allocation).

Yes. Perhaps this helper should be changed/renamed. And perhaps we
can even change __send_signal() to avoid __sigqueue_alloc() if
PF_KTHREAD. Or sig == SIGKILL.

Oleg.

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