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Date:   Sun, 04 Sep 2016 13:29:47 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     torvalds@...ux-foundation.org
Cc:     hannes@...essinduktion.org, rweikusat@...ileactivedefense.com,
        edumazet@...gle.com, w@....eu, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] af_unix: split 'u->readlock' into two: 'iolock'
 and 'bindlock'

From: Linus Torvalds <torvalds@...ux-foundation.org>
Date: Fri, 2 Sep 2016 11:13:09 -0700 (PDT)

> 
> From: Linus Torvalds <torvalds@...ux-foundation.org>
> Date: Thu, 1 Sep 2016 14:43:53 -0700
> Subject: [PATCH 2/2] af_unix: split 'u->readlock' into two: 'iolock' and 'bindlock'
> 
> Right now we use the 'readlock' both for protecting some of the af_unix
> IO path and for making the bind be single-threaded.
> 
> The two are independent, but using the same lock makes for a nasty
> deadlock due to ordering with regards to filesystem locking.  The bind
> locking would want to nest outside the VSF pathname locking, but the IO
> locking wants to nest inside some of those same locks.
> 
> We tried to fix this earlier with commit c845acb324aa ("af_unix: Fix
> splice-bind deadlock") which moved the readlock inside the vfs locks,
> but that caused problems with overlayfs that will then call back into
> filesystem routines that take the lock in the wrong order anyway.
> 
> Splitting the locks means that we can go back to having the bind lock be
> the outermost lock, and we don't have any deadlocks with lock ordering.
> 
> Acked-by: Rainer Weikusat <rweikusat@...eradapt.com>
> Acked-by: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

Applied.

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