six locks: Use atomic_try_cmpxchg_acquire()

This switches to a newer cmpxchg variant which updates @old for us on
failure, simplifying the cmpxchg loops a bit and supposedly generating
better code.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/six.c b/fs/bcachefs/six.c
index 9a5fcd7d35661b74f44554595e3d17774deb4eb6..00580f8ff1c5cd59ce7c72fb729b907d55aa281b 100644 (file)
--- a/fs/bcachefs/six.c
+++ b/fs/bcachefs/six.c
@@ -116,7 +116,7 @@ static int __do_six_trylock(struct six_lock *lock, enum six_lock_type type,
                            struct task_struct *task, bool try)
 {
        int ret;
-       u32 old, new, v;
+       u32 old;
 
        EBUG_ON(type == SIX_LOCK_write && lock->owner != task);
        EBUG_ON(type == SIX_LOCK_write &&
@@ -177,19 +177,14 @@ static int __do_six_trylock(struct six_lock *lock, enum six_lock_type type,
                                ret = -1 - SIX_LOCK_read;
                }
        } else {
-               v = atomic_read(&lock->state);
+               old = atomic_read(&lock->state);
                do {
-                       new = old = v;
-
                        ret = !(old & l[type].lock_fail);
-
                        if (!ret || (type == SIX_LOCK_write && !try)) {
                                smp_mb();
                                break;
                        }
-
-                       new += l[type].lock_val;
-               } while ((v = atomic_cmpxchg_acquire(&lock->state, old, new)) != old);
+               } while (!atomic_try_cmpxchg_acquire(&lock->state, &old, old + l[type].lock_val));
 
                EBUG_ON(ret && !(atomic_read(&lock->state) & l[type].held_mask));
        }
@@ -675,10 +670,10 @@ EXPORT_SYMBOL_GPL(six_lock_downgrade);
  */
 bool six_lock_tryupgrade(struct six_lock *lock)
 {
-       u32 old, new, v = atomic_read(&lock->state);
+       u32 old = atomic_read(&lock->state), new;
 
        do {
-               new = old = v;
+               new = old;
 
                if (new & SIX_LOCK_HELD_intent)
                        return false;
@@ -689,7 +684,7 @@ bool six_lock_tryupgrade(struct six_lock *lock)
                }
 
                new |= SIX_LOCK_HELD_intent;
-       } while ((v = atomic_cmpxchg_acquire(&lock->state, old, new)) != old);
+       } while (!atomic_try_cmpxchg_acquire(&lock->state, &old, new));
 
        if (lock->readers)
                this_cpu_dec(*lock->readers);