On Wed, Aug 30, 2023 at 07:54:13PM -0400, Waiman Long wrote:
On 8/30/23 18:12, Michał Mirosław wrote:Isn't ww_mutex_lock() with ctx = NULL expected to behave like mutex_lock()?
use_ww_ctx is equivalent to ww_ctx != NULL. The one case whereI think ww_mutex_lock() can be called with a NULL ctx. Your patch will
use_ww_ctx was true but ww_ctx == NULL leads to the same
__mutex_add_waiter() call via __ww_mutex_add_waiter().
effectively change those ww_mutex_lock() to be equivalent to mutex_lock().
So it is a behavioral change.
[...]Since now __ww_mutex_add_waiter() is called only with ww_mutex != NULL,
remove the branch there.
I see that there is the rt_mutex version that stubs out@@ -627,12 +624,11 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclasThis one is fine.
debug_mutex_lock_common(lock, &waiter);
waiter.task = current;
- if (use_ww_ctx)
- waiter.ww_ctx = ww_ctx;
+ waiter.ww_ctx = ww_ctx;
lock_contended(&lock->dep_map, ip);That change will break ww_mutex.
- if (!use_ww_ctx) {
+ if (!ww_ctx) {
__ww_mutex_add_waiter(), but its ww_mutex_lock() doesn't use
__mutex_lock_common() at all. With the RT version out of the picture, we
can see that __ww_mutex_add_waiter(), when passed ww_ctx == NULL, just
forwards the work to __ww_waiter_add() with the same arguments
and returns 0 -- making the path exactly as the !use_ww_ctx branch.
Note: There is a lot of templating-via-preprocessor code here and I
might have missed something. I'll appreciate hints here as maybe it
could be made simpler or better understood.