On Fri, Feb 28, 2025 at 06:32:47AM -0800, Sean Christopherson wrote:

On Fri, Feb 28, 2025, Sean Christopherson wrote:

quoted

On Fri, Feb 28, 2025, Lei Yang wrote:

quoted

Hi Keith

V3 introduced a new bug, the following error messages from qemu output
after applying this patch to boot up a guest.

Doh, my bug.  Not yet tested, but this should fix things.  Assuming it does, I'll
post a v3 so I can add my SoB.

         v4

Confirmed that it worked, but deleting the pre-mutex check for ONCE_COMPLETED.
Will post v4 later today.

quoted

diff --git a/include/linux/call_once.h b/include/linux/call_once.h
index ddcfd91493ea..b053f4701c94 100644
--- a/include/linux/call_once.h
+++ b/include/linux/call_once.h

@@ -35,10 +35,12 @@ static inline int call_once(struct once *once, int (*cb)(struct once *))
                return 0;
 
         guard(mutex)(&once->lock);
-        WARN_ON(atomic_read(&once->state) == ONCE_RUNNING);
-        if (atomic_read(&once->state) != ONCE_NOT_STARTED)
+        if (WARN_ON(atomic_read(&once->state) == ONCE_RUNNING))
                 return -EINVAL;
 
+        if (atomic_read(&once->state) == ONCE_COMPLETED)
+                return 0;
+
         atomic_set(&once->state, ONCE_RUNNING);
        r = cb(once);
        if (r)

Possible suggestion since it seems odd to do an atomic_read twice on the
same value. Maybe make this a switch:

	switch (atomic_read(&once->state) {
	case ONCE_NOT_STARTED:
		atomic_set(&once->state, ONCE_RUNNING);
		break;
	case ONCE_COMPLETED:
		return 0;
	case ONCE_RUNNING:
	default:
		WARN_ON(1);
		return -EINVAL;
	}