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Message-ID: <20101208015344.GE29333@dastard> Date: Wed, 8 Dec 2010 12:53:44 +1100 From: Dave Chinner <david@...morbit.com> To: Nick Piggin <npiggin@...nel.dk> Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 02/46] fs: d_validate fixes 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@...morbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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