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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 4a557a5d1a "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 0d98439ea3 ("vfs: use lockred 'dead' flag to
mark unrecoverably dead dentries") and e5c832d555 ("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 b3abd80250 ("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>
This commit is contained in:
Linus Torvalds 2022-07-03 14:40:28 -07:00
parent 4a557a5d1a
commit b8d5109f50
2 changed files with 0 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/lockref.h
View File

@ -38,7 +38,6 @@ extern void lockref_get(struct lockref *);
extern int lockref_put_return(struct lockref *);
extern int lockref_get_not_zero(struct lockref *);
extern int lockref_put_not_zero(struct lockref *);
extern int lockref_get_or_lock(struct lockref *);
extern int lockref_put_or_lock(struct lockref *);
extern void lockref_mark_dead(struct lockref *);

25
lib/lockref.c
View File

@ -110,31 +110,6 @@ 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