From dcbfb2ad3bbd1c3c1b8dab86797e3c1c20a8d31b Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 2 Sep 2013 11:14:19 -0700 Subject: [PATCH] lockref: add 'lockref_get_or_lock() helper This behaves like "lockref_get_not_zero()", but instead of doing nothing if the count was zero, it returns with the lock held. This allows callers to revalidate the lockref-protected data structure if required even if the count was zero to begin with, and possibly increment the count if it passes muster. In particular, the dentry code wants this when it wants to turn an RCU-protected dentry into a stable refcounted one: if the dentry count it zero, but the sequence number still validates the dentry, we can take a reference to it. Signed-off-by: Linus Torvalds --- include/linux/lockref.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/include/linux/lockref.h b/include/linux/lockref.h index 01233e01627ab..0ea026092d1d5 100644 --- a/include/linux/lockref.h +++ b/include/linux/lockref.h @@ -53,6 +53,22 @@ static inline int lockref_get_not_zero(struct lockref *lockref) return retval; } +/** + * lockref_get_or_lock - Increments count unless the count is 0 + * @lockcnt: pointer to lockref structure + * Return: 1 if count updated successfully or 0 if count was zero + * and we got the lock instead. + */ +static inline int lockref_get_or_lock(struct lockref *lockref) +{ + spin_lock(&lockref->lock); + if (!lockref->count) + return 0; + lockref->count++; + spin_unlock(&lockref->lock); + return 1; +} + /** * lockref_put_or_lock - decrements count unless count <= 1 before decrement * @lockcnt: pointer to lockref structure -- 2.39.5