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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id l7sm5733936qtr.87.2021.10.02.10.10.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 02 Oct 2021 10:10:59 -0700 (PDT) Date: Sat, 2 Oct 2021 10:10:40 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.anvils To: Linus Torvalds cc: Steven Rostedt , Hugh Dickins , Daniele Ceraolo Spurio , Matt Roper , Lucas De Marchi , Tvrtko Ursulin , Caz Yokoyama , LKML , Jani Nikula , Matthew Brost , intel-gfx , dri-devel In-Reply-To: Message-ID: <7bad278d-ff81-21aa-48a-b46b9453b2b@google.com> References: <20211002020257.34a0e882@oasis.local.home> <259ff554-76b8-8523-033-9e996f549c70@google.com> <20211002081750.7eec92dd@oasis.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Subject: Re: [Intel-gfx] [BUG 5.15-rc3] kernel BUG at drivers/gpu/drm/i915/i915_sw_fence.c:245! X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Sat, 2 Oct 2021, Linus Torvalds wrote: > On Sat, Oct 2, 2021 at 5:17 AM Steven Rostedt wrote: > > On Sat, 2 Oct 2021 03:17:29 -0700 (PDT) > > Hugh Dickins 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