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From:   Deepa Dinamani <deepa.kernel@gmail.com>
Date:   Tue, 21 May 2019 17:35:38 -0700
Message-ID: <CABeXuvoOGwOGmSz_vgTugLD1NPE=2ULvmESPTtK9d6r8S+WVdQ@mail.gmail.com>
Subject: Re: [PATCH 1/1] signal: Adjust error codes according to restore_user_sigmask()
To:     Eric Wong <e@80x24.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>, dbueso@suse.de, axboe@kernel.dk,
        Davidlohr Bueso <dave@stgolabs.net>,
        Jason Baron <jbaron@akamai.com>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        linux-aio <linux-aio@kvack.org>,
        Omar Kilani <omar.kilani@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, stable@vger.kernel.org,
        Oleg Nesterov <oleg@redhat.com>
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> > > It's been 2 weeks and this fix hasn't appeared in mmots / mmotm.
> > > I also noticed it's missing Cc: for stable@ (below)
> >
> > Why is a -stable backport needed?  I see some talk above about lost
> > signals but it is unclear whether these are being observed after fixing
> > the regression caused by 854a6ed56839a.
>
> I guess Deepa's commit messages wasn't clear...
> I suggest prepending this as the first paragraph to Deepa's
> original message:
>
>   This fixes a bug introduced with 854a6ed56839a which caused
>   EINTR to not be reported to userspace on epoll_pwait.  Failure
>   to report EINTR to userspace caused problems with user code
>   which relies on EINTR to run signal handlers.

This is not what the patch fixed.

The notable change is userspace is that now whenever a signal is
delivered, the return value is adjusted to reflect the signal
delivery.
Prior to this patch, there was a window, however small it might have
been, when the signal was delivered but the errono was not adjusted
appropriately.
This is because of the regression caused by 854a6ed56839a, which
extended the window of delivery of signals that was delivered to
userspace.
The patch also fixes more than sys_epoll_pwait().

I will post a follow up patch.

>
> > IOW, can we please have a changelog which has a clear and complete
> > description of the user-visible effects of the change.
> >
> > And please Cc Oleg.

I will cc Oleg.