linux-kernel - Re: Cheap lock for user mode processes release when process exits

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Message-Id: <20070412194352.a29de6f5.akpm@linux-foundation.org>
Date:	Thu, 12 Apr 2007 19:43:52 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	<mchu@...apoint.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: Cheap lock for user mode processes release when process exits

On Fri, 13 Apr 2007 01:54:28 +0000 (GMT) <mchu@...apoint.com> wrote:

> Hi all,
> 
> Maybe someone here knows better.
> 
> I have several user-mode processes using shared mmap.  There can be several reader processes and only one writer.  Readers access the shared region frequently, writer seldom.
> 
> Naturally, multi-reader/single-writer locks works best.  I tried this with futex on 2.6.9-42.EL.  However, if one of the processes is killed/exits, the lock doesn't get released.
> 
> I can trap the signal to release the lock, but not all signals like kill.
> 
> Anyway I can achieve this without a potential deadlock?
> 

Robust futexes: http://lwn.net/Articles/172149/

But I don't know whether RH backported them into RHEL4.
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