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Message-ID: <20120425130329.GA16413@redhat.com>
Date: Wed, 25 Apr 2012 15:03:29 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Al Viro <viro@...IV.linux.org.uk>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
Russell King <linux@....linux.org.uk>,
Tejun Heo <tj@...nel.org>, Arnd Bergmann <arnd@...db.de>,
Roland McGrath <roland@...k.frob.com>
Subject: Re: [RFC] TIF_NOTIFY_RESUME, arch/*/*/*signal*.c and all such
On 04/25, Al Viro wrote:
>
> On Wed, Apr 25, 2012 at 02:37:46PM +0200, Oleg Nesterov wrote:
> > As for sys_sigsuspend() and this race in particular:
> >
> > > Arrival of a signal that has userland handler
> > > and that isn't blocked by the mask given to sigsuspend() should terminate
> > > sigsuspend().
> >
> > Yes. But note that do_signal() restores the old sigmask. This means that
> > the signal we get after the first do_signal() was not blocked before
> > sigsuspend() was called. So, to some extent, we can pretend that the
> > handler was executed before sigsuspend() and it was never restarted.
>
> Signal might have already arrived by the time we restore sigmask.
Yes, and it sets TIF_SIGPENDING, but unless I missed something this doesn't
matter.
> So no,
> it might have been blocked prior to sigsuspend().
If it was not blocked, then the next do_signal()->get_signal_to_deliver()
returns 0 and clears TIF_SIGPENDING. After that we finally re-enter
sys_sigsuspend() and (assuming it unblocks this sig) notice this pending
signal again and return -EINTR eventually.
Oleg.
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