linux-kernel - Re: [PATCH] fs/9p: fix inode nlink accounting

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Message-ID: <ZZvaRt4T-RjOBoS2@codewreck.org>
Date: Mon, 8 Jan 2024 20:19:34 +0900
From: asmadeus@...ewreck.org
To: Eric Van Hensbergen <ericvh@...nel.org>
Cc: linux-kernel@...r.kernel.org, v9fs@...ts.linux.dev,
	linux_oss@...debyte.com, rminnich@...il.com, lucho@...kov.net
Subject: Re: [PATCH] fs/9p: fix inode nlink accounting

Eric Van Hensbergen wrote on Sun, Jan 07, 2024 at 07:07:52PM +0000:
> I was running some regressions and noticed a (race-y) kernel warning that
> happens when nlink becomes less than zero.  Looking through the code
> it looks like we aren't good about protecting the inode lock when
> manipulating nlink and some code that was added several years ago to
> protect against bugs in underlying file systems nlink handling didn't
> look quite right either.  I took a look at what NFS was doing and tried to
> follow similar approaches in the 9p code.

I was about to say the set/inc/etc_nlink helpers could probably just be
using atomic (there's an atomic_dec_if_postive that we could have used
for the v9fs_dec_count warning), but this isn't our code so not much to
do about that -- I agree it needs a lock.

I didn't take the time to check if you missed any, but it won't be worse
than what we have right now:
Acked-by: Dominique Martinet <asmadeus@...ewreck.org>

-- 
Dominique Martinet | Asmadeus