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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Sebastian Andrzej Siewior , Clark Williams , Simona Vetter , "=?utf-8?B?SsOpcsO0bWU=?= Glisse" , "Christian =?utf-8?B?S8O2bmln?=" , "Paul E. McKenney" , Paolo Bonzini , linux-mm@kvack.org, kvm@vger.kernel.org, linux-rt-devel@lists.linux.dev, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A53414000C X-Stat-Signature: jzdzi9i43kmpmdthxjftqw4jqck34u57 X-Rspam-User: X-HE-Tag: 1786629578-228474 X-HE-Meta: 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 02Gh3I5/ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 13, 2026, David Woodhouse wrote: > On Wed, 2026-08-12 at 15:38 +0100, David Woodhouse wrote: > > On Wed, 2026-08-12 at 11:26 -0300, Jason Gunthorpe wrote: > > > On Wed, Aug 12, 2026 at 03:05:43PM +0100, David Woodhouse wrote: > > > > the non_block_{start,end} guards around the MMU notifiers, which ar= e > > > > basically never being called anyway and don't actually seem to prot= ect > > > > against any real bugs. > > >=20 > > > If you think this blocked stuff is dead code then lets remove it, but > > > I'm pretty sure it is called and I remember seeing bug reports about > > > it being triggered in the wild. Vetter certainly added it because > > > their tests were actually triggering and they had bugs in their DRM > > > stack directly connected to this. > > >=20 > > > It might not trigger for your hypervisor case but we aren't here just > > > to make only kvm work now are we? > >=20 > > I'm sure there can be real-world use cases where it can trigger, but > > when I was *trying* to exercise the code path, to validate my belief > > (from source inspection) that even the plain spinlock would trigger the > > splat, I ended up having to hack the kernel to do so: > >=20 > > https://lore.kernel.org/all/787aa26cf62dfd361eea8ed19f384fc517892501.ca= mel@infradead.org/ > >=20 > > Perhaps in the past it was easier to trigger 'naturally'? >=20 > I did a bit more digging. On the one hand, I was wrong to claim that it > never triggers =E2=80=94 there *are* a handful of reports; of my searches= this > was probably the most fruitful: > https://lore.kernel.org/all/?q=3D%22non_block%3A+1%22 >=20 > On the other hand, they are basically *all* false positives from the > point of view of what the check was actually trying to do. And in KVM. FWIW, all of the KVM false positives are due to PREEMPT_RT turning mmu_lock= into a sleepable lock on x86. So killing off the restriction for PREEMPT_RT wou= ld "fix" the KVM issues. > It's causing more issues than it fixes. Including some bizarre MM > gymnastics: https://lore.kernel.org/all/amMZFqs1smKmMuj5@lucifer/ >=20 > At this point I don't think I even *care* whether we manage to do the > atomic SRCU thing; I think this check should die *anyway*.