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

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Date:	Fri, 16 Nov 2007 11:26:17 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Dan Aloni <da-x@...atomic.org>
CC:	Aristeu Rozanski <aris@...vo.org>,
	Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86_64: fix a deadlock in set_rtc_mmss()

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


Li Zefan
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