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. > > 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. Hugh
