On Sat, 02 Oct 2021, Hugh Dickins <hughd@xxxxxxxxxx> wrote: > On Sat, 2 Oct 2021, Linus Torvalds wrote: >> On Sat, Oct 2, 2021 at 5:17 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: >> > On Sat, 2 Oct 2021 03:17:29 -0700 (PDT) >> > Hugh Dickins <hughd@xxxxxxxxxx> wrote: >> > >> > > Yes (though bisection doesn't work right on this one): the fix >> > >> > Interesting, as it appeared to be very reliable. But I didn't do the >> > "try before / after" on the patch. >> >> Well, even the before/after might well have worked, since the problem >> depended on how that sw_fence_dummy_notify() function ended up >> aligned. So random unrelated changes could re-align it just by >> mistake. > > Yup. > >> >> Patch applied directly. > > Great, thanks a lot. Thanks & sorry, really looks like we managed to drop this between the cracks. :( > >> >> I'd also like to point out how that BUG_ON() actually made things >> worse, and made this harder to debug. If it had been a WARN_ON_ONCE(), >> this would presumably not even have needed bisecting, it would have >> been obvious. >> >> BUG_ON() really is pretty much *always* the wrong thing to do. It >> onl;y results in problems being harder to see because you end up with >> a dead machine and the message is often hidden. > > Jani made the same point. But I guess they then went off into the weeds > of how to recover when warning, that the fix itself did not progress. Yes. That, as well as removing the entire alignment thing to reuse a couple of bits for flags. Too fragile for its own good. BR, Jani. -- Jani Nikula, Intel Open Source Graphics Center
