linux-kernel - Re: [patch 01/28] fs: d

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Message-Id: <20101118.125913.13739447.davem@davemloft.net>
Date:	Thu, 18 Nov 2010 12:59:13 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	npiggin@...nel.dk
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 01/28] fs: d_validate fixes

From: David Miller <davem@...emloft.net>
Date: Thu, 18 Nov 2010 12:51:23 -0800 (PST)

> From: Nick Piggin <npiggin@...nel.dk>
> Date: Wed, 17 Nov 2010 01:09:01 +1100
> 
>> 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.
>> 
>> Signed-off-by: Nick Piggin <npiggin@...nel.dk>
> 
> This won't apply because is conflicts with Christoph Hellwig's
> RCU conversion of d_validate().
> 
> Which is a change that went in more than a month ago.

In fact the conflicts of your patch set are even more pervasive, since
all dcache hash traversals are essentially RCU protected instead of
dcache_lock protected right now.

This makes it very difficult to test or analyze your patches for those
of us on mainline or similar.
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