From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>, Jan Kara <jack@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Jan Kara <jack@suse.com>, Tejun Heo <tj@kernel.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Byungchul Park <byungchul.park@lge.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
vlevenetz@mm-sol.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v10 1/2] printk: Make printk() completely async
Date: Thu, 18 Aug 2016 11:27:12 +0900 [thread overview]
Message-ID: <20160818022712.GB500@swordfish> (raw)
In-Reply-To: <20160812094447.GD7339@pathway.suse.cz>
Hello,
really sorry for very long reply.
On (08/12/16 11:44), Petr Mladek wrote:
[..]
> IMHO, this is fine. We force the synchronous mode in critical
> situations anyway.
yes, I think it makes sense to lower the priority (we also have
briefly discussed this in private emails with Viresh). I'd still
prefer to have forced sync-printk on suspend/hibernate/etc., though.
> But I was curious if we could hit a printk from the wake_up_process().
> The change above causes using the fair scheduler and there is
> the following call chain [*]
>
> vprintk_emit()
> -> wake_up_process()
> -> try_to_wake_up()
> -> ttwu_queue()
> -> ttwu_do_activate()
> -> ttwu_activate()
> -> activate_task()
> -> enqueue_task()
> -> enqueue_task_fair() via p->sched_class->enqueue_task
> -> cfs_rq_of()
> -> task_of()
> -> WARN_ON_ONCE(!entity_is_task(se))
>
> We should never trigger this because printk_kthread is a task.
> But what if the date gets inconsistent?
>
> Then there is the following chain:
>
> vprintk_emit()
> -> wake_up_process()
> -> try_to_wake_up()
> -> ttwu_queue()
> -> ttwu_do_activate()
> -> ttwu_activate()
> -> activate_task()
> -> enqueue_task()
> -> enqueue_task_fair() via p->sched_class->enqueue_task
> ->hrtick_update()
> -> hrtick_start_fair()
> -> WARN_ON(task_rq(p) != rq)
>
> This looks like another paranoid consistency check that might be
> triggered when the scheduler gets messed.
>
> I see few possible solutions:
>
> 1. Replace the WARN_ONs by printk_deferred().
>
> This is the usual solution but it would make debugging less convenient.
what I did internally was a combination of #1 and #3: I introduced a
dump_stack_deferred() function which is basically (almost) a copy-past
of dump_stack() from lib/dump_stack.c with the difference that it calls
printk_deferred(). and added a WARN_ON_DEFERRED() macro.
> 2. Force synchronous printk inside WARN()/BUG() macros.
will it help? semaphore up() calls wake_up_process() regardless the context.
not to mention that we still may have spin_dump() enabled.
> 3. Force printk_deferred() inside WARN()/BUG() macros via the per-CPU
> printk_func.
>
> It might be elegant. But we do not want this outside the scheduler
> code. Therefore we would need special variants of WARN_*_SCHED()
> BUG_*_SCHED() macros.
>
> I personally prefer the 2nd solution. What do you think about it,
> please?
I personally think a combo of #1 and #3 is a bit better than plain #2.
-ss
next prev parent reply other threads:[~2016-08-18 2:27 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-04 16:57 [PATCH v10 0/2] printk: Make printk() completely async Sergey Senozhatsky
2016-04-04 16:57 ` [PATCH v10 1/2] " Sergey Senozhatsky
2016-04-04 22:51 ` Andrew Morton
2016-04-05 5:17 ` Sergey Senozhatsky
2016-04-05 7:39 ` Sergey Senozhatsky
2016-04-06 0:19 ` Sergey Senozhatsky
2016-04-06 8:27 ` Jan Kara
2016-04-07 9:48 ` Sergey Senozhatsky
2016-04-07 12:08 ` Sergey Senozhatsky
2016-04-07 13:15 ` Jan Kara
2016-08-10 21:17 ` Viresh Kumar
2016-08-12 9:44 ` Petr Mladek
2016-08-15 14:26 ` Vladislav Levenetz
2016-08-16 9:04 ` Petr Mladek
2016-08-18 2:27 ` Sergey Senozhatsky [this message]
2016-08-18 9:33 ` Petr Mladek
2016-08-18 9:51 ` Sergey Senozhatsky
2016-08-18 10:56 ` Petr Mladek
2016-08-19 6:32 ` Sergey Senozhatsky
2016-08-19 9:54 ` Petr Mladek
2016-08-19 19:00 ` Jan Kara
2016-08-20 5:24 ` Sergey Senozhatsky
2016-08-22 4:15 ` Sergey Senozhatsky
2016-08-23 12:19 ` Petr Mladek
2016-08-24 1:33 ` Sergey Senozhatsky
2016-08-25 21:10 ` Petr Mladek
2016-08-26 1:56 ` Sergey Senozhatsky
2016-08-26 8:20 ` Sergey Senozhatsky
2016-08-30 9:29 ` Petr Mladek
2016-08-31 2:31 ` Sergey Senozhatsky
2016-08-31 9:38 ` Petr Mladek
2016-08-31 12:52 ` Sergey Senozhatsky
2016-09-01 8:58 ` Petr Mladek
2016-09-02 7:58 ` Sergey Senozhatsky
2016-09-02 15:15 ` Petr Mladek
2016-09-06 7:16 ` Sergey Senozhatsky
2016-08-23 13:03 ` Petr Mladek
2016-08-23 13:48 ` Petr Mladek
2016-04-04 16:57 ` [PATCH v10 2/2] printk: Make wake_up_klogd_work_func() async Sergey Senozhatsky
2016-08-23 3:32 [PATCH v10 1/2] printk: Make printk() completely async Andreas Mohr
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