linux-kernel - Re: [PATCH] tcp: Replace infinite loop on recvmsg bug with proper crash

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Message-ID: <20121107155434.GA17677@redhat.com>
Date:	Wed, 7 Nov 2012 10:54:34 -0500
From:	Dave Jones <davej@...hat.com>
To:	Julius Werner <jwerner@...omium.org>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Patrick McHardy <kaber@...sh.net>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	James Morris <jmorris@...ei.org>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Sameer Nanda <snanda@...omium.org>,
	Mandeep Singh Baines <msb@...omium.org>,
	Eric Dumazet <edumazet@...omium.org>
Subject: Re: [PATCH] tcp: Replace infinite loop on recvmsg bug with proper
 crash

On Tue, Nov 06, 2012 at 05:51:19PM -0800, Julius Werner wrote:
 > > We've had reports of this WARN against the Fedora kernel for a while.
 > > Had this been immediately followed by a BUG(), we'd have never seen those traces at all,
 > > and just got "my machine just locked up" reports instead.
 > >
 > > The proper fix here is to find out why we're getting into this state.
 > 
 > Are you sure you don't mean the WARN below that ("recvmsg bug 2")
 > instead? I don't think this one can happen without eventually running
 > into the syslog overflow issue I described.

bug2 is more common (And usually is accompanied by mangled traces),
but we have reports of the first WARN too..

https://bugzilla.redhat.com/show_bug.cgi?id=841769
https://bugzilla.redhat.com/show_bug.cgi?id=845853
https://bugzilla.redhat.com/show_bug.cgi?id=846991
https://bugzilla.redhat.com/show_bug.cgi?id=860039

(I note that none of these reports mention "also, my hard disk is now full")

 > I agree that the underlying cause must be fixed too, but as we will
 > always have bugs in the kernel I think proper handling when it does
 > happen is also important (and filling the hard disk with junk is
 > obviously not the best approach). If you think a full panic is too
 > extreme, I have an alternative version of this patch that logs the
 > WARN once, closes the socket, and returns EBADFD from the syscall...
 > would you think that is more appropriate?

It sounds more appropriate to me, instead of silently wedging the box.
At least with that approach we have a chance of finding out what happened.

	Dave

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