linux-kernel - Re: [PATCH 2/2] Subject: printk: Don't trap random context in infinite log

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Message-ID: <20171108162813.GA983427@devbig577.frc2.facebook.com>
Date:   Wed, 8 Nov 2017 08:28:13 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org,
        kernel-team@...com, Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/2] Subject: printk: Don't trap random context in
 infinite log_buf flush

Hello, Steven.

On Wed, Nov 08, 2017 at 11:22:29AM -0500, Steven Rostedt wrote:
> > Oh, I was talking about tweaking the repro, but I'm not sure the above
> > would change anything. 
> 
> No, it would change an awful lot.
> 
> It would cause two printers to access the consoles at the same time,
> which would lead to unpredictable behavior.

Sure, I'll give it a shot later but in the repro there literally is no
context which is safe, so I kinda have a difficult time imagining how
that will make things materially better.  Neither of the producers can
get scheduled out no matter they switch back and forth between them or
not, so rcu stalls seem rather unavoidable without introducing an
independent context.

Thanks.

-- 
tejun