linux-kernel - Re: [PATCH] autofs

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Date:	Thu, 24 Apr 2014 12:10:38 +0800
From:	Ian Kent <raven@...maw.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	autofs mailing list <autofs@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] autofs - fix lockref lookup

On Wed, 2014-04-23 at 14:46 -0700, Andrew Morton wrote:
> On Wed, 23 Apr 2014 13:20:36 +0800 Ian Kent <raven@...maw.net> wrote:
> 
> > autofs needs to be able to see private data dentry flags for
> > its dentrys that are being created but not yet hashed and for
> > its dentys that have been rmdir()ed but not yet freed. It
> > needs to do this so it can block processes in these states
> > until a status has been returned to indicate the given
> > operation is complete.
> > 
> > It does this by keeping two lists, active and expring, of
> > dentrys in this state and uses ->d_release() to keep them
> > stable while it checks the reference count to determine
> > if they should be used.
> > 
> > But with the recent lockref changes dentrys being freed
> > sometimes don't transition to a reference count of 0 before
> > being freed so autofs can occassionally use a dentry that
> > is invalid which can lead to a panic.
> 
> What's the value of "recent"?  I assume 3.14 is OK?

I'll need to look again but from memory it's broken from 3.12 onward.

The breakage happened when lockref_mark_dead() was introduced because it
sets lockref->count = -128 instead of reducing count by one as was done
previously.

Ian
  


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