linux-kernel - [BUG] ocfs2/dlm: possible data races in dlm_drop_lockres_ref_done() and dlm_get_lock

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Message-ID: <32dc96d0-2d27-47e4-448a-a42e9ce352af@gmail.com>
Date:   Tue, 13 Jun 2023 15:58:28 +0800
From:   Tuo Li <islituo@...il.com>
To:     mark@...heh.com, jlbec@...lplan.org,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        akpm@...ux-foundation.org
Cc:     ocfs2-devel@....oracle.com,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        baijiaju1990@...look.com
Subject: [BUG] ocfs2/dlm: possible data races in dlm_drop_lockres_ref_done()
 and dlm_get_lock_resource()

Hello,

Our static analysis tool finds some possible data races in the OCFS2 file
system in Linux 6.4.0-rc6.

In most calling contexts, the variables  such as res->lockname.name and
res->owner are accessed with holding the lock res->spinlock. Here is an
example:

   lockres_seq_start() --> Line 539 in dlmdebug.c
     spin_lock(&res->spinlock); --> Line 574 in dlmdebug.c (Lock 
res->spinlock)
     dump_lockres(res, ...); --> Line 575 in fs/ocfs2/dlm/dlmdebug.c
       stringify_lockname(res->lockname.name, ...);  --> Line 493 in 
dlmdebug.c (Access res->lockname.name)
       scnprintf(..., res->owner, ...);  -->Line 498 in dlmdebug.c 
(Access res->owner)

However, in the following calling contexts:

   dlm_deref_lockres_worker() --> Line 2439 in dlmmaster.c
     dlm_drop_lockres_ref_done() --> Line 2459 in dlmmaster.c
       lockname = res->lockname.name; --> Line 2416 in dlmmaster.c 
(Access res->lockname.name)

   dlm_get_lock_resource() --> Line 701 in dlmmaster.c
     if (res->owner != dlm->node_num) --> Line 1023 in dlmmaster.c 
(Access res->owner)

The variables res->lockname.name and res->owner are accessed respectively
without holding the lock res->spinlock, and thus data races can occur.

I am not quite sure whether these possible data races are real and how 
to fix
them if they are real.

Any feedback would be appreciated, thanks!

Reported-by: BassCheck <bass@...a.edu.cn>

Best wishes,
Tuo Li