[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <474DEF79.1080900@o2.pl>
Date: Wed, 28 Nov 2007 23:45:13 +0100
From: Jarek Poplawski <jarkao2@...pl>
To: Larry Finger <larry.finger@...inger.net>
CC: Andreas Schwab <schwab@...e.de>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: Question regarding mutex locking
Larry Finger wrote, On 11/28/2007 04:41 PM:
> Andreas Schwab wrote:
>> 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.
>
> Thank you for that answer. I think that I'm finally beginning to understand.
Probably it would be faster without these "...", which look like
no man's land...
hold_lock = mutex_trylock()
if (hold_lock) {
/* SMP safe */
...
mutex_unlock()
} else {
/* SMP unsafe */
...
/* maybe try again after some break or check */
}
Regards,
Jarek P.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists