Am Dienstag, dem 17.02.2026 um 17:52 +0100 schrieb Bert Karwatzki:

Am Dienstag, dem 17.02.2026 um 12:24 +0100 schrieb Bert Karwatzki:

quoted

Am Dienstag, dem 17.02.2026 um 11:42 +0100 schrieb Bert Karwatzki:

quoted

I just wondered if we can completely skip the

	if (READ_ONCE(txq->xmit_lock_owner) != cpu) {
		[...]
	} else 
	{
		/* "Recursion" alert */
	}
 
check, as the synchronization will we provided by HARD_TX_{LOCK,UNLOCK}.

I thought about that again, and it seems like a bad idea as (in the non-preempt) case
other threads trying to access the queue would wait for the spinlock to be freed, perhaps
one can just change the code like this:

My argument above seems wrong: In the non-preempt case we cannot have another thread accessing the txq
from the same CPU if the lock is taken (it is not preemptible) and for other threads
accessing the txq from different CPUs the check (txq->xmit_lock_owner != cpu) would succeed
and they would try the spinlock anyway, So this would not speak against killing the lock owner
check. As for the recursion detection, perhaps dev_xmit_recursion() is enough?

I tried to research the original commit which introduced the xmit_lock_owner check, but
it is present since linux 2.3.6 (released 19990610) (when __dev_queue_xmit() was still called dev_queue_xmit()),
so I can't tell the original idea behind that check (perhaps recuesion detection ...), so I'm
not completely sure if it can be omitted (and just let dev_xmit_recursion() do the recursion checking).

Bert Karwatzki