linux-kernel - 2.6.27 inotify causes unkillable processes with 100% CPU usage

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Message-Id: <E459FC1E-BD45-459A-A9BD-AC682DBCD2D2@iki.fi>
Date:	Mon, 15 Dec 2008 13:31:29 +0200
From:	Timo Sirainen <tss@....fi>
To:	linux-kernel@...r.kernel.org
Cc:	nuitari-dovecot@...tari.net, Arno Wald <arno.wald@...cologne.de>,
	David Rosenstrauch <darose@...ose.net>
Subject: 2.6.27 inotify causes unkillable processes with 100% CPU usage

There appears to be a bug in 2.6.27 and inotify where it causes  
processes in running state to eat 100% CPU and they can't be killed  
with kill -9, requiring a reboot to get rid of them.

3 people (Cc'd) so far have reported this to me, all of them last  
week. The problem shows up when running my Dovecot IMAP server. Its  
imap processes start hanging, apparently it can happen after running  
for only a couple of minutes:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
6717 arno      20   0  2964 1608 1192 R  100  0.2   1158:05 imap

Only the imap processes hang (Dovecot has a few others). The only  
thing special about it is that it uses inotify. After disabling  
Dovecot's inotify support at least one of the people (Arno) reported  
that he can't reprocuce the bug anymore. He also couldn't reproduce  
the bug with 2.6.26 kernel.

I don't think Dovecot does anything special with its inotify code. It  
just listens on two directories. You can find the code here: http://hg.dovecot.org/dovecot-1.1/file/f9a000ee400d/src/lib/ioloop-notify-inotify.c

Kernels causing the hang:

2.6.27-9.slh.1-sidux-686
Arch Linux, kernel 2.6.27.8
Gentoo with 2.6.27-gentoo-r5, amd64, 2 dual core opterons

Not causing the hang:

2.6.26-6.slh.1-sidux-686

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