Larry Finger wrote, On 11/28/2007 04:41 PM:
> Andreas Schwab wrote:
>> Larry Finger <[EMAIL PROTECTED]> 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.
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