On Sat, May 03, 2025 at 11:19:21PM +0100, David Howells wrote:

Jarkko Sakkinen [off-list ref] wrote:

quoted

Oops, my bad (order swap), sorry. Should have been:
	
 				spin_unlock_irqrestore(&key->user->lock, flags);
			} else {
				smp_mb(); /* key->user before FINAL_PUT set. */
 			}
			set_bit(KEY_FLAG_FINAL_PUT, &key->flags);

Should spin_lock()/unlock() be good enough or what good does smp_mb() do
in that branch? Just checking if I'm missing something before sending
fixed version.

spin_unlock() is semi-permeable, so stuff after it can leak into the inside of
it up as far as the spin_lock().  With your change, the garbage collector can
no longer guarantee that key_put() will have done with accessing key->user
when it sees KEY_FLAG_FINAL_PUT is set.

So, NAK on this patch, I think.  If you want a second opinion, I'd suggest
waving it in front of Paul McKenney.

Fair enough.

If I revisit this in a way or another,  I'll cc to him for comments but
for this I'll buy what you said.

Possibly we only need smp_mb() in the IN_QUOTA branch in key_put().

David

Thank you for the comments.

BR, Jarkko