linux-kernel - Re: dcache shrink list corruption?

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Message-ID: <20140429232013.GM18016@ZenIV.linux.org.uk>
Date:	Wed, 30 Apr 2014 00:20:13 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Chinner <david@...morbit.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: dcache shrink list corruption?

On Tue, Apr 29, 2014 at 04:04:11PM -0700, Linus Torvalds wrote:
> But at a minimum, we have "d_op->d_prune()" that would now be possibly
> be called for the old dentry *after* a new dentry has been allocated.
> Not to mention the inode not having been dropped. So it looks like a
> disaster where the filesystem now ends up having concurrent "live"
> dentries for the same entry.  Even if one of them is on its way out,
> it's still visible to the filesystem. That makes me very
> uncomfortable.
> 
> I'm starting to think that Miklos' original patch (perhaps with the
> spinlock split to at least be one per superblock) is the most
> straightforward approach after all. It's annoying having to add locks
> here, but the whole pruning path should not be a hotpath, so maybe
> it's not actually a big deal.

FWIW, my solution is more or less working; I'll give more local beating
and post it... 
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