linux-kernel - Re: WARNING: ODEBUG bug in get

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Message-ID: <20200827112426.GE28468@redhat.com>
Date:   Thu, 27 Aug 2020 13:24:26 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     syzbot <syzbot+e3cf8f93cf86936710db@...kaller.appspotmail.com>
Cc:     axboe@...nel.dk, linux-kernel@...r.kernel.org,
        peterz@...radead.org, syzkaller-bugs@...glegroups.com
Subject: Re: WARNING: ODEBUG bug in get_signal

On 08/27, syzbot wrote:
>
>  __debug_check_no_obj_freed lib/debugobjects.c:967 [inline]
>  debug_check_no_obj_freed+0x301/0x41c lib/debugobjects.c:998
>  kmem_cache_free.part.0+0x16d/0x1f0 mm/slab.c:3692
>  task_work_run+0xdd/0x190 kernel/task_work.c:141

I don't understand this trace, work->func(work) can call kmem_cache_free()
but task_work_run() doesn't do this.

In theory the patch below makes sense anyway, but I have no idea if it can
explain the problem.

Oleg.

--- x/kernel/task_work.c
+++ x/kernel/task_work.c
@@ -137,7 +137,7 @@ void task_work_run(void)
 		raw_spin_unlock_irq(&task->pi_lock);
 
 		do {
-			next = work->next;
+			next = READ_ONCE(work->next);
 			work->func(work);
 			work = next;
 			cond_resched();