linux-kernel - Re: [PATCH 1/3] printk: Release console_sem after logbuf

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]

Date:	Fri, 10 Jun 2011 11:40:44 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, efault@....de,
	Arne Jansen <lists@...-jansens.de>
Subject: Re: [PATCH 1/3] printk: Release console_sem after logbuf_lock

On Fri, 2011-06-10 at 11:33 +0200, Ingo Molnar wrote:
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > > Some notes:
> > 
> > Stupid thing doesn't explain the magical locking though :( I'm 
> > 99.9% sure that putting an up() inside a spinlock_irq()ed region 
> > was deliberate.
> 
> My guess would be it's done so that pending irqs that have queued up 
> during our current printk-ing activities do not hit us with the 
> console still locked.

Ah, so we already flushed the buffer, but have console_sem locked, so
any interrupt that comes in and prints something will place it in the
buffer but find console_sem is taken, so not flush it.

Then when we're back to doing up() the buffer is filled and nobody will
flush it.

I guess, we can write it like:

	spin_unlock(&logbuf_lock);
	up(&console_sem);
	local_irq_restore(flags);

which would keep interrupt disabled over up(), but have the logbuf_lock
dropped.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/