linux-kernel - Re: possible deadlock in console

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Message-ID: <20190219013254.GA20023@jagdpanzerIV>
Date:   Tue, 19 Feb 2019 10:32:54 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Yao HongBo <yaohongbo@...wei.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linuxarm@...wei.com, linux-kernel@...r.kernel.org
Subject: Re: possible deadlock in console_unlock

On (02/18/19 22:07), Yao HongBo wrote:
> >> I have tried GFP_NOWARN, but the problem still exists.
> >> Only print_safe contexts for tty locks can solve the problem.
> >> My test scenario is falt-injection.
> > 
> > Oh, I see. Yes, fault-injection is special.
> > 
> > I suspect that this patch series can be helpful then
> > https://lore.kernel.org/lkml/20181016050428.17966-1-sergey.senozhatsky@gmail.com/T/#u
> 
> hi, sergey.

Hello,

> I merged this patch series on linux-4.19.18, but it didn't work for the fault-injection cases.

Thanks!

> The failure seems to be the same as before.

OK... So tty_port lock must switch to printk_safe, after all...
I had it in one of the previous versions of the patchset which you
have tested, but people were strictly against new locking rules
in TTY, so I dropped that part. Need to think what we can do here.

BTW,
we are now looking at a completely new printk implementation; which
would not use printk_safe at all:
https://lore.kernel.org/lkml/20190212143003.48446-1-john.ogness@linutronix.de/T/#u

	-ss