Message-ID: <474CFA64.8050608@lwfinger.net>
Date: Tue, 27 Nov 2007 23:19:32 -0600
From: Larry Finger <larry.finger@lwfinger.net>
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To: Robert Hancock <hancockr@shaw.ca>
CC: LKML <linux-kernel@vger.kernel.org>
Subject: Re: Question regarding mutex locking
References: <fa.C9TdvYAhY8SablNc39IpD8WDnNM@ifi.uio.no> <474CF440.2000001@shaw.ca>
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Robert Hancock wrote:
> Larry Finger wrote:
>> If a particular routine needs to lock a mutex, but it may be entered
>> with that mutex already locked,
>> would the following code be SMP safe?
>>
>> hold_lock = mutex_trylock()
>>
>> ..
>>
>> if (hold_lock)
>>     mutex_unlock()
> 
> Not if another task could be acquiring that lock at the same time, which
> is probably the case, otherwise you wouldn't need the mutex. In other
> words, if you're going to do this, you might as well toss the mutex
> entirely as it's about the same effect..
> 

Thanks for the help. Someday, I hope to understand this stuff.

Larry

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