Messages in this thread | | | Date | Sat, 2 Oct 2021 10:10:40 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: [BUG 5.15-rc3] kernel BUG at drivers/gpu/drm/i915/i915_sw_fence.c:245! |
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On Sat, 2 Oct 2021, Linus Torvalds wrote: > On Sat, Oct 2, 2021 at 5:17 AM Steven Rostedt <rostedt@goodmis.org> wrote: > > On Sat, 2 Oct 2021 03:17:29 -0700 (PDT) > > Hugh Dickins <hughd@google.com> 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
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