From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 15339 invoked by alias); 24 Jan 2007 17:30:15 -0000 Received: (qmail 15331 invoked by uid 22791); 24 Jan 2007 17:30:14 -0000 X-Spam-Status: No, hits=-2.4 required=5.0 tests=AWL,BAYES_00,FORGED_RCVD_HELO X-Spam-Check-By: sourceware.org Received: from tomts20.bellnexxia.net (HELO tomts20-srv.bellnexxia.net) (209.226.175.74) by sourceware.org (qpsmtpd/0.31) with ESMTP; Wed, 24 Jan 2007 17:30:01 +0000 Received: from krystal.dyndns.org ([67.68.204.133]) by tomts20-srv.bellnexxia.net (InterMail vM.5.01.06.13 201-253-122-130-113-20050324) with ESMTP id <20070124172958.ENIS24907.tomts20-srv.bellnexxia.net@krystal.dyndns.org> for ; Wed, 24 Jan 2007 12:29:58 -0500 Received: from localhost (localhost [127.0.0.1]) (uid 1000) by krystal.dyndns.org with local; Wed, 24 Jan 2007 12:24:45 -0500 id 001D2812.45B7965D.0000174B Date: Wed, 24 Jan 2007 17:30:00 -0000 From: Mathieu Desnoyers To: Andrew Morton Cc: Greg Kroah-Hartman , Richard J Moore , linux-kernel@vger.kernel.org, "Martin J. Bligh" , Christoph Hellwig , Douglas Niehaus , Ingo Molnar , ltt-dev@shafik.org, systemtap@sources.redhat.com, Thomas Gleixner Subject: [PATCH] order of lockdep off/on in vprintk() should be changed Message-ID: <20070124172445.GA1145@Krystal> References: <20061220235216.GA28643@Krystal> <20070116175624.GA16022@Krystal> <20070123202637.970e467b.akpm@osdl.org> <20070124165150.GC4979@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20070124165150.GC4979@Krystal> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.4.32-grsec (i686) X-Uptime: 12:16:56 up 154 days, 14:24, 4 users, load average: 0.70, 0.74, 0.74 User-Agent: Mutt/1.5.13 (2006-08-11) X-IsSubscribed: yes Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2007-q1/txt/msg00189.txt.bz2 The order of locking between lockdep_off/on() and local_irq_save/restore() in vprintk() should be changed. * In kernel/printk.c : vprintk() does : preempt_disable() local_irq_save() lockdep_off() spin_lock(&logbuf_lock) spin_unlock(&logbuf_lock) if(!down_trylock(&console_sem)) up(&console_sem) lockdep_on() local_irq_restore() preempt_enable() The goals here is to make sure we do not call printk() recursively from kernel/lockdep.c:__lock_acquire() (called from spin_* and down/up) nor from kernel/lockdep.c:trace_hardirqs_on/off() (called from local_irq_restore/save). It can then potentially call printk() through mark_held_locks/mark_lock. It correctly protects against the spin_lock call and the up/down call, but it does not protect against local_irq_restore. It could cause infinite recursive printk/trace_hardirqs_on() calls when printk() is called from the mark_lock() error handing path. We should change the locking so it becomes correct : preempt_disable() lockdep_off() local_irq_save() spin_lock(&logbuf_lock) spin_unlock(&logbuf_lock) if(!down_trylock(&console_sem)) up(&console_sem) local_irq_restore() lockdep_on() preempt_enable() Signed-off-by: Mathieu Desnoyers --- a/kernel/printk.c +++ b/kernel/printk.c @@ -530,8 +530,8 @@ asmlinkage int vprintk(const char *fmt, va_list args) zap_locks(); /* This stops the holder of console_sem just where we want him */ - local_irq_save(flags); lockdep_off(); + local_irq_save(flags); spin_lock(&logbuf_lock); printk_cpu = smp_processor_id(); @@ -640,8 +640,8 @@ asmlinkage int vprintk(const char *fmt, va_list args) console_locked = 0; up(&console_sem); } - lockdep_on(); local_irq_restore(flags); + lockdep_on(); } else { /* * Someone else owns the drivers. We drop the spinlock, which @@ -650,8 +650,8 @@ asmlinkage int vprintk(const char *fmt, va_list args) */ printk_cpu = UINT_MAX; spin_unlock(&logbuf_lock); - lockdep_on(); local_irq_restore(flags); + lockdep_on(); } preempt_enable(); -- OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68