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Date: Fri, 1 Oct 2004 14:55:36 -0700
From: Andrew Morton <akpm@osdl.org>
To: Badari Pulavarty <pbadari@us.ibm.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2.6.9-rc2-mm4 ps hang ?
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Badari Pulavarty <pbadari@us.ibm.com> wrote:
>
> > Can you work out who is holding mmap_sem for writing?
> > 
> 
> grr.. okay. It hangs randomly. Don't we have code to record the holder
> of a sem somewhere ?

The full sysrq-T trace should tell us.  All I saw from your initial email
was two processes stuck in down_read().  That shouldn't happen, so either
there was another process in down_write() somewhere or we mucked up the
semaphore (it is corrupted, or someone forget up_write()).