From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757735Ab1FINOY (ORCPT ); Thu, 9 Jun 2011 09:14:24 -0400 Received: from casper.infradead.org ([85.118.1.10]:39529 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757403Ab1FINOV (ORCPT ); Thu, 9 Jun 2011 09:14:21 -0400 Message-Id: <20110609131307.493181962@chello.nl> User-Agent: quilt/0.48-1 Date: Thu, 09 Jun 2011 15:06:48 +0200 From: Peter Zijlstra To: Linus Torvalds , Ingo Molnar , Thomas Gleixner Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, efault@gmx.de, Arne Jansen , Peter Zijlstra Subject: [PATCH 1/3] printk: Release console_sem after logbuf_lock References: <20110609130647.937204592@chello.nl> Content-Disposition: inline; filename=printk-up-after-unlock.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Release console_sem after unlocking the logbuf_lock so that we don't generate wakeups while holding logbuf_lock. This avoids some lock inversion troubles once we remove the lockdep_off bits between logbuf_lock and rq->lock (prints while holding rq->lock vs doing wakeups while holding logbuf_lock). There's of course still an actual deadlock where the printk()s under rq->lock will issue a wakeup from the up() call. Signed-off-by: Peter Zijlstra --- kernel/printk.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) Index: linux-2.6/kernel/printk.c =================================================================== --- linux-2.6.orig/kernel/printk.c +++ linux-2.6/kernel/printk.c @@ -782,7 +782,7 @@ static inline int can_use_console(unsign static int console_trylock_for_printk(unsigned int cpu) __releases(&logbuf_lock) { - int retval = 0; + int retval = 0, wake = 0; if (console_trylock()) { retval = 1; @@ -795,12 +795,14 @@ static int console_trylock_for_printk(un */ if (!can_use_console(cpu)) { console_locked = 0; - up(&console_sem); + wake = 1; retval = 0; } } printk_cpu = UINT_MAX; spin_unlock(&logbuf_lock); + if (wake) + up(&console_sem); return retval; } static const char recursion_bug_msg [] = @@ -1271,8 +1273,8 @@ void console_unlock(void) if (unlikely(exclusive_console)) exclusive_console = NULL; - up(&console_sem); spin_unlock_irqrestore(&logbuf_lock, flags); + up(&console_sem); if (wake_klogd) wake_up_klogd(); }