linux-kernel - Re: [PATCH 0/2] lockdep vs recursive read locks

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Message-ID: <Pine.LNX.4.64.0803131124220.17196@blonde.site>
Date:	Thu, 13 Mar 2008 11:25:28 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: Re: [PATCH 0/2] lockdep vs recursive read locks

On Wed, 12 Mar 2008, Peter Zijlstra wrote:
> We seemed to have some lockdep trouble wrt recursive read locks. Today Gautham
> asked me some specific questions about it, which led to these patches.
> 
> IIRC Hugh ran into something similar a while back. This hopefully fixes it.

Hmm, I don't remember that myself: can you jog my memory?

What I do remember is that when I fixed madvise(MADV_REMOVE i.e. holepunch)
not to hold mmap_sem (at that time down_write but today down_read, though
would still be bad) across vmtruncate_range which takes i_mutex (contrast
writing from an unfaulted area that takes i_mutex then down_read mmap_sem),
Ingo asked me offline if lockdep caught that and it didn't.  Just tried
again now, with your patches applied, and madvise_remove restored to its
old misbehaviour, and it looks like lockdep still doesn't catch it
(but suspect me of pilot error if you find otherwise).

Hugh
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