[PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock+ local_irq_save, especially when CONFIG_LOCKDEP not defined

From: Chen Gang
Date: Tue Jun 18 2013 - 23:00:16 EST

When CONFIG_LOCKDEP is not defined, spin_lock_irqsave() is not equal to
spin_lock() + local_irq_save().

In __mod_timer(), After call spin_lock_irqsave() with 'base->lock' in
lock_timer_base(), it may use spin_lock() with the 'new_base->lock'.

It may let original call do_raw_spin_lock_flags() with 'base->lock',
but new call LOCK_CONTENDED() with 'new_base->lock'.

In fact, we need both of them call do_raw_spin_lock_flags(), so use
spin_lock_irqsave() instead of spin_lock() + local_irq_save().

Signed-off-by: Chen Gang <gang.chen@xxxxxxxxxxx>
kernel/timer.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/timer.c b/kernel/timer.c
index aa8b964..2550a62 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -754,9 +754,9 @@ __mod_timer(struct timer_list *timer, unsigned long expires,
if (likely(base->running_timer != timer)) {
/* See the comment in lock_timer_base() */
timer_set_base(timer, NULL);
- spin_unlock(&base->lock);
+ spin_unlock_irqrestore(&base->lock, flags);
base = new_base;
- spin_lock(&base->lock);
+ spin_lock_irqsave(&base->lock, flags);
timer_set_base(timer, base);
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/