linux-kernel - Re: 2.6.35-rc3 deadlocks on semaphore operations

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Date:	Mon, 21 Jun 2010 22:01:18 +0200
From:	Luca Tettamanti <kronos.it@...il.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Julia Lawall <julia@...u.dk>,
	Manfred Spraul <manfred@...orfullife.com>
Subject: Re: 2.6.35-rc3 deadlocks on semaphore operations

On Fri, Jun 18, 2010 at 09:49:44AM -0500, Christoph Lameter wrote:
> Can produce it with make-kpkg building a kernel.
[...]
> linux-2.6$ strace -p21561
> Process 21561 attached - interrupt to quit
> semop(32768, {{0, -1, SEM_UNDO}}, 1
> 
> linux-2.6$ strace -p21751
> Process 21751 attached - interrupt to quit
> semop(32768, {{0, -1, SEM_UNDO}}, 1
> 
> linux-2.6$ strace -p21792
> Process 21792 attached - interrupt to quit
> semop(32768, {{0, -1, SEM_UNDO}}, 1
> 
> linux-2.6$ strace -p21793
> Process 21793 attached - interrupt to quit
> semop(32768, {{0, -1, SEM_UNDO}}, 1

Ah! I was trying to understand what was going on with apache... I see
the same symptoms with apache and prefork module: each child serves one
request and then just hangs until it's recycled.
Strace shows the same semop syscall.

# ipcs

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status      

------ Semaphore Arrays --------
key        semid      owner      perms      nsems     
0x00000000 65536      www-data   600        1         

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    

# cat /proc/sysvipc/sem
       key      semid perms      nsems   uid   gid  cuid  cgid      otime      ctime
         0      65536   600          1    33    33     0     0 1277149940 1277149903

# /tmp/getall 65536 -v
getall <id> [-v]
found 1 semaphores.
   0:   0 (cnt   4 zcnt   0)


Luca
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