[PATCH 2/4] ucount: Replace get_ucounts_or_wrap() with atomic_inc_not_zero().

[Sebastian Andrzej Siewior]

get_ucounts_or_wrap() increments the counter and if the counter is
negative then it decrements it again in order to reset the previous increment.
This statement can be replaced with atomic_inc_not_zero() to only
increment the counter if it is not yet 0.
This simplifies the get function because the put (if the get failed) can
be removed. atomic_inc_not_zero() is implement as a cmpxchg() loop which
can be repeated several times if another get/put is performed in parallel. This
will be optimized later.

Increment the reference counter only if not yet dropped to zero.

Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
 kernel/ucount.c | 24 ++++++------------------
 1 file changed, 6 insertions(+), 18 deletions(-)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index 86c5f1c0bad90..4aa5011538257 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -146,25 +146,16 @@ static void hlist_add_ucounts(struct ucounts *ucounts)
        spin_unlock_irq(&ucounts_lock);
 }
 
-static inline bool get_ucounts_or_wrap(struct ucounts *ucounts)
-{
-       /* Returns true on a successful get, false if the count wraps. */
-       return !atomic_add_negative(1, &ucounts->count);
-}
-
 struct ucounts *get_ucounts(struct ucounts *ucounts)
 {
-       if (!get_ucounts_or_wrap(ucounts)) {
-               put_ucounts(ucounts);
-               ucounts = NULL;
-       }
-       return ucounts;
+       if (atomic_inc_not_zero(&ucounts->count))
+               return ucounts;
+       return NULL;
 }
 
 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
        struct hlist_head *hashent = ucounts_hashentry(ns, uid);
-       bool wrapped;
        struct ucounts *ucounts, *new = NULL;
 
        spin_lock_irq(&ucounts_lock);
@@ -189,14 +180,11 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, 
kuid_t uid)
                        return new;
                }
        }
-
-       wrapped = !get_ucounts_or_wrap(ucounts);
+       if (!atomic_inc_not_zero(&ucounts->count))
+               ucounts = NULL;
        spin_unlock_irq(&ucounts_lock);
        kfree(new);
-       if (wrapped) {
-               put_ucounts(ucounts);
-               return NULL;
-       }
+
        return ucounts;
 }
 
-- 
2.47.2