linux-kernel - Re: Question regarding mutex locking

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Message-ID: <jemysy2y3y.fsf@sykes.suse.de>
Date:	Wed, 28 Nov 2007 16:22:57 +0100
From:	Andreas Schwab <schwab@...e.de>
To:	Larry Finger <Larry.Finger@...inger.net>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Question regarding mutex locking

Larry Finger <Larry.Finger@...inger.net> writes:

> 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()

When two CPUs may enter the critical region at the same time, what is
the point of the mutex?  Also, the first CPU may unlock the mutex while
the second one is still inside the critical region.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@...e.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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