linux-kernel - Re: [PATCH 1/2] vfs: dcache: fix deadlock in tree traversal

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Message-ID: <CA+55aFxeghUVxiFS=P+ck_BCnOuMm=HFAkqTBccxJoubk96afQ@mail.gmail.com>
Date:	Mon, 17 Sep 2012 15:09:39 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Miklos Szeredi <miklos@...redi.hu>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	Trond.Myklebust@...app.com
Subject: Re: [PATCH 1/2] vfs: dcache: fix deadlock in tree traversal

On Mon, Sep 17, 2012 at 1:39 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> Egads...  The problem is real and analysis, AFAICS, is correct, but result
> is extremely ugly ;-/

Agreed.

The problem (or at least one *part* of the problem) is that the "goto
rename_retry" case is done for two different entities entirely:

 - the "try_to_ascend()" failure path, which can happen even when
renamelock is held for writing.

 - the "if we weren't write-locked before, and the read-lock failed"
case (which obviously cannot happen if we already held things for
writing)

That said, I'm not sure why/how that try_to_ascend() could even fail
when we're holding things locked. I guess it's the DCACHE_DISCONNECTED
case that triggers.

So I'll ignore this series for now, hoping that Al will send a nicer
version. Al, Miklos, please make sure this issue doesn't get dropped
by mistake.

            Linus
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