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From: Larry Finger <larry.finger@lwfinger.net>
To: Robert Hancock <hancockr@shaw.ca>
Cc: LKML <linux-kernel@vger.kernel.org>
Subject: Re: Question regarding mutex locking
Date: Tue, 27 Nov 2007 23:19:32 -0600	[thread overview]
Message-ID: <474CFA64.8050608@lwfinger.net> (raw)
In-Reply-To: <474CF440.2000001@shaw.ca>

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


  reply	other threads:[~2007-11-28  5:19 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <fa.C9TdvYAhY8SablNc39IpD8WDnNM@ifi.uio.no>
2007-11-28  4:53 ` Question regarding mutex locking Robert Hancock
2007-11-28  5:19   ` Larry Finger [this message]
2007-11-29  2:34     ` David Schwartz
2007-11-29  7:56       ` Jarek Poplawski
2007-11-28  4:37 Larry Finger
2007-11-28  8:10 ` Matthias Kaehlcke
2007-11-28 14:46   ` Larry Finger
2007-11-28 15:00     ` Matthias Kaehlcke
2007-11-28 15:22 ` Andreas Schwab
2007-11-28 15:41   ` Larry Finger
2007-11-28 22:45     ` Jarek Poplawski
2007-11-28 22:56       ` Jarek Poplawski
2007-11-28 23:07         ` Jarek Poplawski
2007-11-28 23:33       ` Stephen Hemminger
2007-11-29  6:40         ` Jarek Poplawski
2007-11-30  1:13 ` Bryan O'Sullivan

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