MIME-Version: 1.0
From: Andy Lutomirski <luto@kernel.org>
Date: Wed, 30 Dec 2015 03:18:11 -0800
Message-ID: <CALCETrUHFDdfPymKfD2TJHL6w-C5dc675xuJfk=c=-twsPZqqA@mail.gmail.com>
Subject: Linux 4.4-rc4 regression, bisected to "net: fix sock_wake_async() rcu protection"
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>, Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Linus Torvalds <torvalds@linux-foundation.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On recent v4.4-rc releases, I can't run emacs.  No, really, running
"emacs" in a GNOME 3 session makes gnome-shell think that emacs is
running, but no window is drawn, and the overall system UI is a bit
weird when the invisible emacs window is focused.

This is 100% reproducible.

There might be other symptoms involving gdb malfunctioning, but those
are, at best, sporadic.  The emacs failure is entirely reliable.  I
have no idea what the underlying failure mode is, but failure to wake
a socket waiter seems plausible,  I also have no idea why oocalc,
gimp, vim, gedit, firefox, etc aren't affected.

A somewhat unorthodox "git bisect" run blames:

commit ceb5d58b217098a657f3850b7a2640f995032e62
Author: Eric Dumazet <edumazet@google.com>
Date:   Sun Nov 29 20:03:11 2015 -0800

    net: fix sock_wake_async() rcu protection

I've confirmed that v4.4-rc7 with that patch reverted works fine.

Since the offending commit was apparently a security fix, simply
reverting it might not be the best idea.

--Andy
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