iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

six locks: Use atomic_try_cmpxchg_acquire()

Browse Source 
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>
This commit is contained in:
Kent Overstreet 2023-05-25 14:35:06 -04:00
parent c4687a4a75
commit 2d9200cfe0
1 changed files with 6 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
fs/bcachefs/six.c
View File

@ -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);