linux-kernel - Re: [syzbot] [kernel?] possible deadlock in stack_depot

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Message-ID: <317e077b-71a7-4112-a7d0-5c49efce4f39@I-love.SAKURA.ne.jp>
Date:   Tue, 5 Dec 2023 21:00:46 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+186b55175d8360728234@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        John Ogness <john.ogness@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [kernel?] possible deadlock in stack_depot_put

On 2023/12/05 20:31, Hillf Danton wrote:
> Unlike down_trylock(), mutex_trylock() is unable to trigger any lockdep
> warning, so why is a binary semaphore prefered over mutex?

The mutex has limitations which makes it impossible to use for console lock.

https://elixir.bootlin.com/linux/v6.7-rc4/source/kernel/locking/mutex.c#L537

By the way, this is a KASAN bug saying "refcount_t: underflow; use-after-free.".
Possibly a candidate for printk_deferred_enter() user?