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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" , Sean Christopherson , 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: <20260812160751.GE662699@ziepe.ca> References: <37b83b429b9f14ea6ad4ca1c13cc8e565ec09033.camel@infradead.org> <44c51ace9b0dc44b795f6f48c91cda440eed910b.camel@infradead.org> <20260812122759.GA662699@ziepe.ca> <20260812134934.GC662699@ziepe.ca> Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Aug 12, 2026 at 06:04:47PM +0200, Paolo Bonzini wrote: > > + * Atomic-flavor readers run with preemption disabled, so every > > + * read-side critical section is bounded and running (not blocked) on > > + * some CPU, which is what makes spinning here sane: the wait is > > + * bounded by the longest such section. No index flip and no > > + * grace-period sequence update occur, so concurrent call_srcu(), > > + * synchronize_srcu() and srcu_barrier() are entirely unaffected. > > Making synchronize_srcu_atomic() spin in CONFIG_PREEMPT_RT is a > slightly tall request - it's basically putting it on the same level as > raw_spinlock. But if the MMU notifier guys really want to make OOM > notifiers atomic, this would be basically the only way to do so. IMHO it is fine if PREEMPT_RT does something else, just that the normal cases should follow the current arrangment where it is atomic > If instead it's okay to remove nonblock_start/end under > CONFIG_PREEMPT_RT, for RT kernels I'd rather avoid This seems well agreed at least Jason