linux-kernel - Re: possible deadlock in console

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Message-ID: <20190216073856.GA9979@tigerII.localdomain>
Date:   Sat, 16 Feb 2019 16:46:17 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Yao HongBo <yaohongbo@...wei.com>, linuxarm@...wei.com,
        linux-kernel@...r.kernel.org
Subject: Re: possible deadlock in console_unlock

On (02/16/19 16:21), Sergey Senozhatsky wrote:
> On (02/16/19 14:36), Yao HongBo wrote:
> > hi, sergey:
> > 
> > As shown in that link, https://lkml.org/lkml/2018/6/6/397
> > 
> > On the linux kernel 5.0-rc6, Syzkaller also hit 'possible deadlock in console_unlock'
> > bug for several times in my environment.
> > 
> > This solution fixes things for me. Do you have a plan to submit patches to
> > solve this problem.
> > 
> > diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> > 	__printk_safe_enter();
> > 	kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
> > 	__printk_safe_exit();
> 
> I would probably try the following:

Yao HongBo, could you please post the lockdep splat?

GFP_NOWARN is probably the best option for now. Yes, it, maybe,
will not work for fault-injection cases; but printk_safe approach
is harder to push for, especially given that printk_safe maybe will
not even exist in the future.

	-ss