From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756800AbZAIUcB (ORCPT ); Fri, 9 Jan 2009 15:32:01 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756573AbZAIUbO (ORCPT ); Fri, 9 Jan 2009 15:31:14 -0500 Received: from bee.hiwaay.net ([216.180.54.11]:38448 "EHLO bee.hiwaay.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756449AbZAIUbM (ORCPT ); Fri, 9 Jan 2009 15:31:12 -0500 Date: Fri, 9 Jan 2009 14:31:10 -0600 From: Chris Adams To: linux-kernel@vger.kernel.org Subject: [PATCH] Fix leap second message hang Message-ID: <20090109203110.GA1523360@hiwaay.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Resending this outside the big long thread to make sure it gets added (it isn't critical right now but I don't want to forget it). From: Chris Adams The code to handle leap seconds printks an information message when the second is inserted or deleted. It does this while holding xtime_lock. However, printk wakes up klogd, and in some cases, the scheduler tries to get the current kernel time, trying to get xtime_lock (which results in a deadlock). This moved the printks outside of the lock. It also adds a comment to not use printk while holding xtime_lock. Signed-off-by: Chris Adams Acked-by: Linas Vepstas --- diff -urpN linux-2.6.28-git5-vanilla/include/linux/time.h linux-2.6.28-git5/include/linux/time.h --- linux-2.6.28-git5-vanilla/include/linux/time.h 2009-01-02 22:09:10.000000000 -0600 +++ linux-2.6.28-git5/include/linux/time.h 2009-01-03 11:57:27.000000000 -0600 @@ -99,6 +99,12 @@ static inline struct timespec timespec_s extern struct timespec xtime; extern struct timespec wall_to_monotonic; + +/* + * Do not call printk while holding this lock; it wakes klogd and the + * scheduler may try to get the current kernel time, which will try to get + * this lock. + */ extern seqlock_t xtime_lock; extern unsigned long read_persistent_clock(void); diff -urpN linux-2.6.28-git5-vanilla/kernel/time/ntp.c linux-2.6.28-git5/kernel/time/ntp.c --- linux-2.6.28-git5-vanilla/kernel/time/ntp.c 2009-01-02 22:09:34.000000000 -0600 +++ linux-2.6.28-git5/kernel/time/ntp.c 2009-01-03 11:57:46.000000000 -0600 @@ -130,6 +130,7 @@ void ntp_clear(void) static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer) { enum hrtimer_restart res = HRTIMER_NORESTART; + const char *msg = NULL; write_seqlock(&xtime_lock); @@ -140,8 +141,7 @@ static enum hrtimer_restart ntp_leap_sec xtime.tv_sec--; wall_to_monotonic.tv_sec++; time_state = TIME_OOP; - printk(KERN_NOTICE "Clock: " - "inserting leap second 23:59:60 UTC\n"); + msg = "Clock: inserting leap second 23:59:60 UTC"; hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC); res = HRTIMER_RESTART; break; @@ -150,8 +150,7 @@ static enum hrtimer_restart ntp_leap_sec time_tai--; wall_to_monotonic.tv_sec--; time_state = TIME_WAIT; - printk(KERN_NOTICE "Clock: " - "deleting leap second 23:59:59 UTC\n"); + msg = "Clock: deleting leap second 23:59:59 UTC"; break; case TIME_OOP: time_tai++; @@ -166,6 +165,9 @@ static enum hrtimer_restart ntp_leap_sec write_sequnlock(&xtime_lock); + if (msg) + printk(KERN_NOTICE "%s\n", msg); + return res; }