linux-kernel - Re: [External] Re: [PATCH 2/2] sched: mark PRINTK_DEFERRED_CONTEXT_MASK in _

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Message-ID: <20200928235052.GB871730@jagdpanzerIV.localdomain>
Date:   Tue, 29 Sep 2020 08:50:52 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Chengming Zhou <zhouchengming@...edance.com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        pmladek@...e.com, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, songmuchun@...edance.com,
        john.ogness@...utronix.de
Subject: Re: [External] Re: [PATCH 2/2] sched: mark
 PRINTK_DEFERRED_CONTEXT_MASK in __schedule()

On (20/09/28 12:25), Peter Zijlstra wrote:
[..]
> > printk
> >   vprintk_emit
> >     console_unlock
> >       vt_console_print
> >         hide_cursor
> >           bit_cursor
> >             soft_cursor
> >               queue_work_on
> >                 __queue_work
> >                   try_to_wake_up
> >                     _raw_spin_lock
> >                       native_queued_spin_lock_slowpath
> > 
> > Looks like it's introduced by this commit:
> > 
> > eaa434defaca1781fb2932c685289b610aeb8b4b
> > 
> > "drm/fb-helper: Add fb_deferred_io support"
> 
> Oh gawd, yeah, all the !serial consoles are utter batshit.
> 
> Please look at John's last printk rewrite, IIRC it farms all that off to
> a kernel thread instead of doing it from the printk() caller's context.

Not yet. Scheduler is still part of the printk() - either in the
form of !serial consoles or console_sem, or both.

	-ss