From: Jan Kara <jack@suse.cz>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jan Kara <jack@suse.cz>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Byungchul Park <byungchul.park@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.com>, Petr Mladek <pmladek@suse.com>,
Tejun Heo <tj@kernel.org>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async
Date: Mon, 21 Mar 2016 16:33:05 +0100 [thread overview]
Message-ID: <20160321153305.GA31279@quack.suse.cz> (raw)
In-Reply-To: <20160321145832.GA545@swordfish>
On Mon 21-03-16 23:58:32, Sergey Senozhatsky wrote:
> Hello Jan,
>
> On (03/21/16 15:32), Jan Kara wrote:
> [..]
> > > we have 2 spin locks in vprintk_emit() -- logbuf_lock and sem->lock. and N
> > > CPUs can concurrently lockup on those two locks, which already makes a
> > > single static pointer in spiun_dump() questionable.
> > >
> > > logbug_lock *theoretically* can detect and handle recursive printk()s,
> > > there is no way to catch sem->lock spin_dump() at the moment (but that's
> > > not the point).
> > >
> > > there are 2 new spin locks in vprintk_emit() -- p->pi_lock and rq->lock.
> >
> > Actually, this is not true. These locks are already in vprintk_emit() via
> > the up(&console_sem) call from console_unlock() since up() can call
> > wake_up() which needs the same locks as wake_up_process().
>
> true. I meant new locks (which come with printk_kthread). the already
> existing locks and problems were not addressed.
>
> > And by calling wake_up_process() under logbuf_lock, you actually introduce
> > recursion issues for printk_deferred() messages which are supposed to be
> > working from under rq->lock and similar. So I think you have to keep this
> > section outside of logbuf_lock.
>
> hm, in_sched (printk_deferred()) messages are printed by
> irq work->wake_up_klogd_work_func(), not by wake_up_process()
> from vprintk_emit(). or am I missing something?
Think of following:
some function
printk()
vprintk_emit()
spin_lock(&logbuf_lock);
...
wake_up_process()
printk_deferred()
vprintk_emit() -> recursion on logbuf_lock
Previously scheduler code was allowed to call printk_deferred() wherever it
wanted...
So we are not supposed to call into the scheduler from under logbuf_lock...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2016-03-21 15:32 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-20 14:13 [RFC][PATCH v5 0/2] printk: Make printk() completely async Sergey Senozhatsky
2016-03-20 14:13 ` [RFC][PATCH v5 1/2] " Sergey Senozhatsky
2016-03-21 0:06 ` Byungchul Park
2016-03-21 0:43 ` Sergey Senozhatsky
2016-03-21 0:56 ` Byungchul Park
2016-03-21 7:35 ` Sergey Senozhatsky
2016-03-21 8:07 ` Byungchul Park
2016-03-21 8:47 ` Byungchul Park
2016-03-21 9:28 ` Sergey Senozhatsky
2016-03-21 14:32 ` Jan Kara
2016-03-21 14:58 ` Sergey Senozhatsky
2016-03-21 15:33 ` Jan Kara [this message]
2016-03-21 17:11 ` Sergey Senozhatsky
2016-03-22 2:18 ` Byungchul Park
2016-03-22 2:13 ` Byungchul Park
2016-03-22 5:52 ` Sergey Senozhatsky
2016-03-22 6:57 ` Byungchul Park
2016-03-22 7:43 ` Sergey Senozhatsky
2016-03-21 8:51 ` Sergey Senozhatsky
2016-03-20 14:13 ` [RFC][PATCH v5 2/2] printk: Make wake_up_klogd_work_func() async Sergey Senozhatsky
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