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	Thu, 09 Nov 2023 20:39:27 +0000
Date: Thu, 9 Nov 2023 20:39:26 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Christian Brauner <brauner@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 09/22] fast_dput(): handle underflows gracefully
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Thu, Nov 09, 2023 at 03:46:21PM +0100, Christian Brauner wrote:
> On Thu, Nov 09, 2023 at 06:20:43AM +0000, Al Viro wrote:
> > If refcount is less than 1, we should just warn, unlock dentry and
> > return true, so that the caller doesn't try to do anything else.
> 
> That's effectively to guard against bugs in filesystems, not in dcache
> itself, right? Have we observed this frequently?

Hard to tell - it doesn't happen often, but... extra dput() somewhere
is not an impossible class of bugs.  I remember running into that
while doing work in namei.c, I certainly have seen failure exits in
random places that fucked refcounting up by dropping the wrong things.