Date: Wed, 8 Dec 2010 12:53:44 +1100
From: Dave Chinner <david@fromorbit.com>
To: Nick Piggin <npiggin@kernel.dk>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 02/46] fs: d_validate fixes
Message-ID: <20101208015344.GE29333@dastard>
References: <cover.1290852958.git.npiggin@kernel.dk>
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On Sat, Nov 27, 2010 at 08:44:32PM +1100, Nick Piggin wrote:
> d_validate has been broken for a long time.
> 
> kmem_ptr_validate does not guarantee that a pointer can be dereferenced
> if it can go away at any time. Even rcu_read_lock doesn't help, because
> the pointer might be queued in RCU callbacks but not executed yet.
> 
> So the parent cannot be checked, nor the name hashed. The dentry pointer
> can not be touched until it can be verified under lock. Hashing simply
> cannot be used.
> 
> Instead, verify the parent/child relationship by traversing parent's
> d_child list. It's slow, but only ncpfs and the destaged smbfs care
> about it, at this point.

I'd drop the previous revert patch and just convert the RCU hash
traversal straight to the d_child traversal code you introduce here.
This is a much better explanation of why the d_validate mechanism
needs to be changed, and the revert is really an unnecessary extra
step...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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