linux-kernel - Re: [PATCH 7/9] liblockdep: Support using LD

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Date:	Wed, 08 May 2013 09:29:45 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	torvalds@...ux-foundation.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/9] liblockdep: Support using LD_PRELOAD

Peter,

Thanks for your comments! I'll address them and re-send the patch series.

On 05/08/2013 06:22 AM, Peter Zijlstra wrote:
>> +	/*
>> > +	 * Some programs attempt to initialize and use locks in their
>> > +	 * allocation path. This means that a call to malloc() would
>> > +	 * result in locks being initialized and locked.
>> > +	 *
>> > +	 * Why is it an issue for us? dlsym() below will try allocating to
>> > +	 * give us the original function. Since this allocation will result
>> > +	 * in a locking operations, we have to let pthread deal with it,
>> > +	 * but we can't! we don't have the pointer to the original API
>> > +	 * since we're inside dlsym() trying to get it :(
>> > +	 *
>> > +	 * We can work around it by telling the program that locking was
>> > +	 * really okay, and just initialize those locks when we're fully
>> > +	 * up and running (this is ok because this all happens during
>> > +	 * initialization phase, when we have just one thread). But
>> > +	 * this is a big TODO at this point.
>> > +	 */
> Fun.. got any example programs that trigger this?

firefox.

The problem there is that it uses jemalloc, which tries to do what I've
described in the blurb above.


Thanks,
Sasha
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