linux-kernel - [PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock + local_irq_save, especially when CONFIG

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Date:	Wed, 19 Jun 2013 10:59:15 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock
 + local_irq_save, especially when CONFIG_LOCKDEP not defined


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@...anux.com>
---
 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);
 		}
 	}
-- 
1.7.7.6
--
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