[tip:timers/urgent] clocksource: Resume clocksource without taking the clocksource mutex

[tip-bot for Martin Schwidefsky <schwidefsky@de.ibm.com>]

Commit-ID:  89133f93508137231251543d1732da638e6022e1
Gitweb:     http://git.kernel.org/tip/89133f93508137231251543d1732da638e6022e1
Author:     Martin Schwidefsky <schwidefsky@de.ibm.com>
AuthorDate: Thu, 24 Sep 2009 17:29:52 +0200
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 24 Sep 2009 22:37:53 +0200

clocksource: Resume clocksource without taking the clocksource mutex

git commit 75c5158f70c065b9 converted the clocksource spinlock to a
mutex. This causes the following BUG:

BUG: sleeping function called from invalid context at
kernel/mutex.c:280 in_atomic(): 0, irqs_disabled(): 1, pid: 2473,
name: pm-suspend 2 locks held by pm-suspend/2473:
 #0:  (&buffer->mutex){......}, at: [<ffffffff8115ab13>]
sysfs_write_file+0x3c/0x137
 #1:  (pm_mutex){......}, at: [<ffffffff810865b5>]
enter_state+0x39/0x130 Pid: 2473, comm: pm-suspend Not tainted 2.6.31
#1 Call Trace:
 [<ffffffff810792f0>] ? __debug_show_held_locks+0x22/0x24
 [<ffffffff8104a2ef>] __might_sleep+0x107/0x10b
 [<ffffffff8141fca9>] mutex_lock_nested+0x25/0x43
 [<ffffffff81073537>] clocksource_resume+0x1c/0x60
 [<ffffffff81072902>] timekeeping_resume+0x1e/0x1c8
 [<ffffffff812aee62>] __sysdev_resume+0x25/0xcf
 [<ffffffff812aef79>] sysdev_resume+0x6d/0xae
 [<ffffffff810864f8>] suspend_devices_and_enter+0x12b/0x1af
 [<ffffffff8108665b>] enter_state+0xdf/0x130
 [<ffffffff81085dc3>] state_store+0xb6/0xd3
 [<ffffffff81204c73>] kobj_attr_store+0x17/0x19
 [<ffffffff8115abd2>] sysfs_write_file+0xfb/0x137
 [<ffffffff811057d2>] vfs_write+0xae/0x10b
 [<ffffffff81208392>] ? __up_read+0x1a/0x7f
 [<ffffffff811058ef>] sys_write+0x4a/0x6e
 [<ffffffff81011b82>] system_call_fastpath+0x16/0x1b

clocksource_resume is called early in the resume process, there is
only one cpu, no processes are running and the interrupts are
disabled. It is therefore possible to resume the clocksources
without taking the clocksource mutex.

Reported-by: Xiaotian Feng <xtfeng@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Tested-by: Michal Schmidt <mschmidt@redhat.com>
Cc: Xiaotian Feng <xtfeng@gmail.com>
Cc: John Stultz <johnstul@us.ibm.com>
LKML-Reference: <20090924172952.49697825@mschwide.boeblingen.de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
 kernel/time/clocksource.c |    4 ----
 1 files changed, 0 insertions(+), 4 deletions(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 0911334..5e18c6a 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -394,15 +394,11 @@ void clocksource_resume(void)
 {
 	struct clocksource *cs;
 
-	mutex_lock(&clocksource_mutex);
-
 	list_for_each_entry(cs, &clocksource_list, list)
 		if (cs->resume)
 			cs->resume();
 
 	clocksource_resume_watchdog();
-
-	mutex_unlock(&clocksource_mutex);
 }
 
 /**