Hi,
(2013/07/09 10:09), Waiman Long wrote:> +/**
> + * lockref_put_or_lock - decrements count unless count <= 1 before decrement
> + * @lockcnt: pointer to lockref structure
> + * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
> + *
> + * The only difference between lockref_put_or_lock and lockref_put is that
> + * the former function will hold the lock on return while the latter one
> + * will free it on return.
> + */
> +static __always_inline int lockref_put_or_locked(struct lockref *lockcnt)
Here is a function name typo. _locked should be _lock.
And also, I think we should take a note here to tell this function does *not*
guarantee lockcnt->refcnt == 0 or 1 until unlocked if this returns 0.
> +{
> + spin_lock(&lockcnt->lock);
> + if (likely(lockcnt->refcnt > 1)) {
> + lockcnt->refcnt--;
> + spin_unlock(&lockcnt->lock);
> + return 1;
> + }
> + return 0;
> +}
Using this implementation guarantees lockcnt->refcnt == 0 or 1 until unlocked
if this returns 0.
However, the below one looks not guarantee it. Since lockref_add_unless
and spinlock are not done atomically, there is a chance for someone
to increment it right before locking.
Or, I missed something?
> +/**
> + * lockref_put_or_lock - Decrements count unless the count is <= 1
> + * otherwise, the lock will be taken
> + * @lockcnt: pointer to struct lockref structure
> + * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
> + */
> +int
> +lockref_put_or_lock(struct lockref *lockcnt)
> +{
> + if (lockref_add_unless(lockcnt, -1, 1))
> + return 1;
> + spin_lock(&lockcnt->lock);
> + return 0;
> +}
BTW, it looks that your dcache patch knows this and keeps double check for
the case of lockcnt->refcnt > 1 in dput().
Thank you,
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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