linux-kernel - Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160321171105.GA1809@swordfish>
Date:	Tue, 22 Mar 2016 02:11:05 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Byungchul Park <byungchul.park@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.com>, Petr Mladek <pmladek@...e.com>,
	Tejun Heo <tj@...nel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH v5 1/2] printk: Make printk() completely async

On (03/21/16 16:33), Jan Kara wrote:
[..]
> > > 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

uh, indeed. I was more concerned about printk() calls that are
troublemakers and are already in wake_up_process() - spin_dump()s.
but yes, braking printk_deferred() in this case is a regression.
thanks for pointing that out. and also thanks to Byungchul.

	-ss

> 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@...e.com>
> SUSE Labs, CR
>