linux-kernel - Re: [RFC PATCH] shrink_dcache

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Date:	Tue, 10 Jan 2012 16:15:17 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	mgorman@...e.de, gregkh@...e.de, akpm@...ux-foundation.org
Subject: Re: [RFC PATCH] shrink_dcache_parent() deadlock

On Tue, Jan 10, 2012 at 08:00:30AM -0800, Linus Torvalds wrote:
> On Tue, Jan 10, 2012 at 2:05 AM, Miklos Szeredi <miklos@...redi.hu> wrote:
> >
> > I tested Dave's patch and the bug can still be easily reproduced.
> >
> > And that's to be expected, as the intermediate "being on the lru"
> > state that Dave's patch eliminates doesn't play a fundamental part in
> > the mechanism of the livelock. ?It does eliminate one trylock, but
> > that's not the one critical to this bug (removing it is a very good
> > idea anyway).
> >
> > The critical trylock here is the one in dentry_kill() which tries to
> > lock the parent.
> 
> Ok. Here's your patch munged for current -git. You've got most of a
> changelog, can you send this out with the right subject and a
> sign-off, and re-test with the current git just to make sure.
> 
> Al, do you want to handle this or should I take it directly?

I'll pick it once Miklos posts it.

> I'm assuming nobody has any objections to Miklos' patch?

I'm fine with it.

ObGrrr: I'm down to two remaining d_alloc_root() callers and while
neither is buggy per se, looking around a bit has turned up breakage
in both cases ;-/  (coda lookup treating OOM in new_inode() as
"not found" rather than -ENOMEM and hfs+ mount not bothering to check
if allocation *or* disk IO might fail, with very ugly results)...
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