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McKenney" , Sean Christopherson , Paolo Bonzini , linux-mm@kvack.org, kvm@vger.kernel.org, linux-rt-devel@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/mmu_notifier: Remove non_block_start/end() from notifier invocation Message-ID: <20260812122759.GA662699@ziepe.ca> References: <20260811135537.GC544626@ziepe.ca> <1d669aca4ffee797b9c29215382444a5b23624b3.camel@infradead.org> <20260811142730.GG544626@ziepe.ca> <20260811104229.72fdd928@gandalf.local.home> <37b83b429b9f14ea6ad4ca1c13cc8e565ec09033.camel@infradead.org> <44c51ace9b0dc44b795f6f48c91cda440eed910b.camel@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <44c51ace9b0dc44b795f6f48c91cda440eed910b.camel@infradead.org> X-Rspam-User: X-Rspamd-Queue-Id: 40FCE40007 X-Rspamd-Server: rspam07 X-Stat-Signature: wyixgcgo9hahmboq95gq74nmtp9bozoa X-HE-Tag: 1786537682-995608 X-HE-Meta: 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 VEkd53ZN wfWib6nRDjSM0e0Kf2flS4ZyO+DUTkEIK2PRfN0rYJvDBxHPIy16Cx+aftZFBC9i8D5km0VzJXuuDh27srfU+l95YPC8DZXXCn9lb75bx7793Ld1DLe6PYysSQCpDcFTaSgfM+R1qQzJyM0S5tN8B5sQYYfPaLHIWRCQOpsvfOh185E+r8cKKw8/XNDDY9NoXehzuXLCadGiFnagdIOg6Vmg6W60poy16NQUW7UFG+X42Bwf7MVhYnuDHDllQEKa0+BPj5dSWwbQxASx9wRhDkaAPfkclHgrk2D4FhCNo1m2BcIkELt+gVVYx7oJ/ak7O+hXNv4F137MbaB/qLCM0I6cltlY76k7Yt/tMftRzYG4DS8yoSKpQf6939BZLVlDYM+KsLw69QiPg38D2QfFfQd/6AicCuFiQkD+2 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 12, 2026 at 09:21:31AM +0100, David Woodhouse wrote: > On Wed, 2026-08-12 at 10:14 +0200, Michal Hocko wrote: > > On Tue 11-08-26 16:24:48, David Woodhouse wrote: > > [...] > > > I had a second reason for disabling the overzealous check too: to allow > > > SRCU grace periods within the notifier callbacks. > > > > Is there a way that srcu barrier could cause an indirect dependency on > > memory allocation? In other words what might block the scru to complete? > > Not after https://lore.kernel.org/all/6eed3fe3461e9690b486ca98fa7563f60d3940ff.camel@infradead.org/ The user of the SRCU might have a read side that wraps an allocate. In general it is not safe. I'm skeptical that without special API and documentation the KVM special use of SRCU you've outlined will not remain working long term too.. Jason