From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751091AbWAYSAT (ORCPT ); Wed, 25 Jan 2006 13:00:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751090AbWAYSAT (ORCPT ); Wed, 25 Jan 2006 13:00:19 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:53194 "EHLO mx3.mail.elte.hu") by vger.kernel.org with ESMTP id S1751091AbWAYSAS (ORCPT ); Wed, 25 Jan 2006 13:00:18 -0500 Date: Wed, 25 Jan 2006 19:00:32 +0100 From: Ingo Molnar To: John Stultz Cc: Andrew Morton , Thomas Gleixner , linux-kernel@vger.kernel.org, Arjan van de Ven Subject: [patch, validator] fix clocksource_lock deadlock Message-ID: <20060125180032.GA11734@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=AWL autolearn=no SpamAssassin version=3.0.3 0.0 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org clocksource_lock is used in softirq-context via e.g. timeofday_periodic_hook() -> get_next_clocksource(), but the lock is not acquired in a softirq-safe manner - which could lead to deadlocks. this bug was found via the lock validator i'm working on: ============================ [ BUG: illegal lock usage! ] ---------------------------- illegal {used-in-softirq} -> {enabled-softirqs} usage. swapper/1 [HC0[0]:SC0[0]:HE1:SE1] takes {clocksource_lock [u:21]}, at: [] register_clocksource+0x16/0xf0 {used-in-softirq} state was registered at: [] get_next_clocksource+0xd/0x40 hardirqs last enabled at: [] vprintk+0x28a/0x3e0 softirqs last enabled at: [] irq_exit+0x39/0x50 other info that might help in debugging this: ------------------------------ | showing all locks held by: | (swapper/1 [c30d7790, 125]): ------------------------------ [] show_trace+0xd/0x10 [] dump_stack+0x17/0x20 [] print_usage_bug+0x1e2/0x200 [] mark_lock+0x28d/0x2a0 [] debug_lock_chain+0x6a5/0x10d0 [] debug_lock_chain_spin+0x3d/0x60 [] _raw_spin_lock+0x2d/0x90 [] _spin_lock+0x8/0x10 [] register_clocksource+0x16/0xf0 [] init_pit_clocksource+0x57/0x90 [] init+0xfa/0x3e0 [] kernel_thread_helper+0x5/0x10 the fix is to lock clocksource_lock in a softirq-safe way. (with this patch applied, the timeofday code validates fine.) Signed-off-by: Ingo Molnar ---- kernel/time/clocksource.c | 31 +++++++++++++++++-------------- 1 files changed, 17 insertions(+), 14 deletions(-) Index: linux/kernel/time/clocksource.c =================================================================== --- linux.orig/kernel/time/clocksource.c +++ linux/kernel/time/clocksource.c @@ -48,6 +48,9 @@ extern struct clocksource clocksource_ji static struct clocksource *curr_clocksource = &clocksource_jiffies; static struct clocksource *next_clocksource; static LIST_HEAD(clocksource_list); +/* + * May be used in softirq context too: + */ static DEFINE_SPINLOCK(clocksource_lock); static char override_name[32]; @@ -70,12 +73,12 @@ late_initcall(clocksource_done_booting); */ struct clocksource *get_next_clocksource(void) { - spin_lock(&clocksource_lock); + spin_lock_bh(&clocksource_lock); if (next_clocksource && finished_booting) { curr_clocksource = next_clocksource; next_clocksource = NULL; } - spin_unlock(&clocksource_lock); + spin_unlock_bh(&clocksource_lock); return curr_clocksource; } @@ -141,7 +144,7 @@ static int is_registered_source(struct c */ void register_clocksource(struct clocksource *c) { - spin_lock(&clocksource_lock); + spin_lock_bh(&clocksource_lock); /* check if clocksource is already registered */ if (is_registered_source(c)) { @@ -152,7 +155,7 @@ void register_clocksource(struct clockso /* select next clocksource */ next_clocksource = select_clocksource(); } - spin_unlock(&clocksource_lock); + spin_unlock_bh(&clocksource_lock); } EXPORT_SYMBOL(register_clocksource); @@ -166,9 +169,9 @@ EXPORT_SYMBOL(register_clocksource); */ void reselect_clocksource(void) { - spin_lock(&clocksource_lock); + spin_lock_bh(&clocksource_lock); next_clocksource = select_clocksource(); - spin_unlock(&clocksource_lock); + spin_unlock_bh(&clocksource_lock); } /** @@ -183,9 +186,9 @@ sysfs_show_current_clocksources(struct s { char *curr = buf; - spin_lock(&clocksource_lock); + spin_lock_bh(&clocksource_lock); curr += sprintf(curr, "%s ", curr_clocksource->name); - spin_unlock(&clocksource_lock); + spin_unlock_bh(&clocksource_lock); curr += sprintf(curr, "\n"); @@ -214,7 +217,7 @@ static ssize_t sysfs_override_clocksourc if (count < 1) return -EINVAL; - spin_lock(&clocksource_lock); + spin_lock_bh(&clocksource_lock); /* copy the name given: */ memcpy(override_name, buf, count); @@ -223,7 +226,7 @@ static ssize_t sysfs_override_clocksourc /* try to select it: */ next_clocksource = select_clocksource(); - spin_unlock(&clocksource_lock); + spin_unlock_bh(&clocksource_lock); return count; } @@ -241,14 +244,14 @@ sysfs_show_available_clocksources(struct struct list_head *tmp; char *curr = buf; - spin_lock(&clocksource_lock); + spin_lock_bh(&clocksource_lock); list_for_each(tmp, &clocksource_list) { struct clocksource *src; src = list_entry(tmp, struct clocksource, list); curr += sprintf(curr, "%s ", src->name); } - spin_unlock(&clocksource_lock); + spin_unlock_bh(&clocksource_lock); curr += sprintf(curr, "\n"); @@ -301,10 +304,10 @@ device_initcall(init_clocksource_sysfs); */ static int __init boot_override_clocksource(char* str) { - spin_lock(&clocksource_lock); + spin_lock_bh(&clocksource_lock); if (str) strlcpy(override_name, str, sizeof(override_name)); - spin_unlock(&clocksource_lock); + spin_unlock_bh(&clocksource_lock); return 1; }