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Date: Wed, 25 Apr 2012 15:32:09 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org, Russell King <linux@arm.linux.org.uk>,
        Tejun Heo <tj@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Roland McGrath <roland@hack.frob.com>
Subject: Re: [RFC] TIF_NOTIFY_RESUME, arch/*/*/*signal*.c and all such
Message-ID: <20120425133209.GA17900@redhat.com>
References: <20120420160848.GG6871@ZenIV.linux.org.uk> <20120420164239.GH6871@ZenIV.linux.org.uk> <CA+55aFzuTspDyyLaOA-g-dTWydaUeeWo9uVGR+rZ=ZJzPW_Ocw@mail.gmail.com> <20120420180748.GI6871@ZenIV.linux.org.uk> <20120423180150.GA6871@ZenIV.linux.org.uk> <20120424072617.GB6871@ZenIV.linux.org.uk> <20120425030659.GE6871@ZenIV.linux.org.uk> <20120425123746.GA15560@redhat.com> <20120425125042.GF6871@ZenIV.linux.org.uk> <20120425130329.GA16413@redhat.com>
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On 04/25, Oleg Nesterov wrote:
>
> 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,
        ^^^^^^^
I meant, If it WAS 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.