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authorLinus Torvalds <torvalds@linux-foundation.org>2022-07-03 14:40:28 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-07-03 14:40:28 -0700
commitb8d5109f50969ead9d49c3e8bd78ec1f82e548e3 (patch)
treedfb65d5b767f91e4518e74138a485719814b43ac /lib/lockref.c
parent4a557a5d1a6145ea586dc9b17a9b4e5190c9c017 (diff)
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lockref: remove unused 'lockref_get_or_lock()' function
Looking at the conditional lock acquire functions in the kernel due to the new sparse support (see commit 4a557a5d1a61 "sparse: introduce conditional lock acquire function attribute"), it became obvious that the lockref code has a couple of them, but they don't match the usual naming convention for the other ones, and their return value logic is also reversed. In the other very similar places, the naming pattern is '*_and_lock()' (eg 'atomic_put_and_lock()' and 'refcount_dec_and_lock()'), and the function returns true when the lock is taken. The lockref code is superficially very similar to the refcount code, only with the special "atomic wrt the embedded lock" semantics. But instead of the '*_and_lock()' naming it uses '*_or_lock()'. And instead of returning true in case it took the lock, it returns true if it *didn't* take the lock. Now, arguably the reflock code is quite logical: it really is a "either decrement _or_ lock" kind of situation - and the return value is about whether the operation succeeded without any special care needed. So despite the similarities, the differences do make some sense, and maybe it's not worth trying to unify the different conditional locking primitives in this area. But while looking at this all, it did become obvious that the 'lockref_get_or_lock()' function hasn't actually had any users for almost a decade. The only user it ever had was the shortlived 'd_rcu_to_refcount()' function, and it got removed and replaced with 'lockref_get_not_dead()' back in 2013 in commits 0d98439ea3c6 ("vfs: use lockred 'dead' flag to mark unrecoverably dead dentries") and e5c832d55588 ("vfs: fix dentry RCU to refcounting possibly sleeping dput()") In fact, that single use was removed less than a week after the whole function was introduced in commit b3abd80250c1 ("lockref: add 'lockref_get_or_lock() helper") so this function has been around for a decade, but only had a user for six days. Let's just put this mis-designed and unused function out of its misery. We can think about the naming and semantic oddities of the remaining 'lockref_put_or_lock()' later, but at least that function has users. And while the naming is different and the return value doesn't match, that function matches the whole '{atomic,refcount}_dec_and_test()' pattern much better (ie the magic happens when the count goes down to zero, not when it is incremented from zero). Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/lockref.c')
-rw-r--r--lib/lockref.c25
1 files changed, 0 insertions, 25 deletions
diff --git a/lib/lockref.c b/lib/lockref.c
index c6f0b183b937..45e93ece8ba0 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -111,31 +111,6 @@ int lockref_put_not_zero(struct lockref *lockref)
EXPORT_SYMBOL(lockref_put_not_zero);
/**
- * lockref_get_or_lock - Increments count unless the count is 0 or dead
- * @lockref: pointer to lockref structure
- * Return: 1 if count updated successfully or 0 if count was zero
- * and we got the lock instead.
- */
-int lockref_get_or_lock(struct lockref *lockref)
-{
- CMPXCHG_LOOP(
- new.count++;
- if (old.count <= 0)
- break;
- ,
- return 1;
- );
-
- spin_lock(&lockref->lock);
- if (lockref->count <= 0)
- return 0;
- lockref->count++;
- spin_unlock(&lockref->lock);
- return 1;
-}
-EXPORT_SYMBOL(lockref_get_or_lock);
-
-/**
* lockref_put_return - Decrement reference count if possible
* @lockref: pointer to lockref structure
*