linux-kernel - Re: [PATCH 1/2] cgroup-v1: Fix missing mutex

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Message-ID: <mqzlqupbzt4zlsphipac4qz75uzzhcbiuxez2bupmcatp32hkw@y4ltledez5y2>
Date: Fri, 18 Jul 2025 14:55:14 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Zijiang Huang <huangzjsmile@...il.com>
Cc: tj@...nel.org, hannes@...xchg.org, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Zijiang Huang <kerayhuang@...cent.com>, 
	Hao Peng <flyingpeng@...cent.com>
Subject: Re: [PATCH 1/2] cgroup-v1: Fix missing mutex_unlock in error paths

On Fri, Jul 18, 2025 at 07:54:08PM +0800, Zijiang Huang <huangzjsmile@...il.com> wrote:
> In the function, after acquiring the mutex with mutex_lock, multiple return
> paths (such as returning ERR_PTR, NULL, or normal pointers)fail to call
> mutex_unlock to release the lock, which could lead to deadlock risks.

You've almost convinced me that you've found a case for the scoped
locks. However, this patch doesn't look correct -- the lock is released
in cgroup_pidlist_stop() + the comment in fs/kernfs/file.c:

 * As kernfs_seq_stop() is also called after kernfs_seq_start() or
 * kernfs_seq_next() failure,

Or have you found a path where the pairing is unmatched?

Thanks,
Michal

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