linux-kernel - Re: Question regarding mutex locking

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Message-ID: <474D7F5B.9090008@lwfinger.net>
Date:	Wed, 28 Nov 2007 08:46:51 -0600
From:	Larry Finger <larry.finger@...inger.net>
To:	Matthias Kaehlcke <matthias.kaehlcke@...il.com>,
	Larry Finger <Larry.Finger@...inger.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Question regarding mutex locking

Matthias Kaehlcke wrote:
> El Tue, Nov 27, 2007 at 10:37:00PM -0600 Larry Finger ha dit:
> 
>> 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()
> 
> this is wont work, a mutex must not be released from another
> context than the one that acquired it.

I thought that mutex_trylock() returned 1 if it got the lock and 0 if not. If that is true, wouldn't
the if statement only unlock if the lock was obtained in this routine?

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