linux-kernel - Re: [PATCH] x86_64: fix a deadlock in set_rtc

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Date:	Sat, 17 Nov 2007 10:34:52 +0200
From:	Dan Aloni <da-x@...atomic.org>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Aristeu Rozanski <aris@...vo.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86_64: fix a deadlock in set_rtc_mmss()

On Fri, Nov 16, 2007 at 11:26:17AM +0800, Li Zefan wrote:
> Aristeu Rozanski wrote:
> > Hello Dan,
> >> Patch is valid only for 2.6.23.x, guessing from the recent arch/ changes 
> >> in 2.6.24-rc.
> >>
> >> set_rtc_mmss() was used to be called from interrupt context in 2.6.22,
> >> however in 2.6.23, it is called from a timer context, where interrupts
> >> are enabled. This patch ensures that rtc_interrupt() won't dead-lock 
> >> with set_rtc_mmss().
> > 
> >> diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
> >> index 6241b50..8414236 100644
> >> --- a/arch/x86_64/kernel/time.c
> >> +++ b/arch/x86_64/kernel/time.c
> >> @@ -87,13 +87,14 @@ static int set_rtc_mmss(unsigned long nowtime)
> >>  	int retval = 0;
> >>  	int real_seconds, real_minutes, cmos_minutes;
> >>  	unsigned char control, freq_select;
> >> +	unsigned long flags;
> >>  
> >>  /*
> >>   * IRQs are disabled when we're called from the timer interrupt,
> >>   * no need for spin_lock_irqsave()
> >>   */
> >>  
> >> -	spin_lock(&rtc_lock);
> >> +	spin_lock_irqsave(&rtc_lock, flags);
> > I think it's a good idea to update or just remove the comment above.
> > 
> 
> David P. Reed has sent a patch to fix this bug before you.
> 
> http://lkml.org/lkml/2007/11/14/435

Yes, missed by a day. Although that patch was aimed for 2.6.24-rc, 
I am currently more concerned about the 2.6.23.x tree.

Greg, can this be added to 2.6.23-stable?

Signed-off-by: Dan Aloni <da-x@...atomic.org>

---
commit 26c05aa66d10e95de63d95a348023ada4827ceed
tree 7c12f2b35fcba31c9f62ba278b9d232406f80e83
parent ad1765c56c2178a09e87d123548a35f221e1fc05
author Dan Aloni <da-x@...atomic.org> Sat, 17 Nov 2007 10:31:01 +0200
committer Dan Aloni <da-x@...atomic.org> Sat, 17 Nov 2007 10:31:01 +0200

 arch/x86_64/kernel/time.c |   10 +++-------
 1 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 6d48a4e..fde5796 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -87,13 +87,9 @@ static int set_rtc_mmss(unsigned long nowtime)
 	int retval = 0;
 	int real_seconds, real_minutes, cmos_minutes;
 	unsigned char control, freq_select;
+	unsigned long flags;
 
-/*
- * IRQs are disabled when we're called from the timer interrupt,
- * no need for spin_lock_irqsave()
- */
-
-	spin_lock(&rtc_lock);
+	spin_lock_irqsave(&rtc_lock, flags);
 
 /*
  * Tell the clock it's being set and stop it.
@@ -143,7 +139,7 @@ static int set_rtc_mmss(unsigned long nowtime)
 	CMOS_WRITE(control, RTC_CONTROL);
 	CMOS_WRITE(freq_select, RTC_FREQ_SELECT);
 
-	spin_unlock(&rtc_lock);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	return retval;
 }


-- 
Dan Aloni
XIV LTD, http://www.xivstorage.com
da-x (at) monatomic.org, dan (at) xiv.co.il
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