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([2405:4802:21dc:72d0:50b1:2f22:32bb:703]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cc1f3312676sm4204321a12.12.2026.08.31.06.55.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Aug 2026 06:55:52 -0700 (PDT) From: ThangNN99 To: linux-kernel@vger.kernel.org Cc: linux-rt-devel@lists.linux.dev, linux-mm@kvack.org, Vlastimil Babka , Harry Yoo , Sebastian Andrzej Siewior Subject: Re: [PATCH v3] mm/slab: don't use kfree_rcu sheaves on PREEMPT_RT in kvfree_call_rcu() Date: Mon, 31 Aug 2026 20:55:46 +0700 Message-ID: <20260831135546.9929-1-ngocthang2710.1999@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260831135150.1B4B31F00A3E@smtp.kernel.org> References: <20260831135150.1B4B31F00A3E@smtp.kernel.org> Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Thanks, both are pre-existing and out of scope for this patch: - The GFP_NOWAIT/wakeup_kswapd() concern in __kfree_rcu_sheaf() applies identically before and after this patch on !PREEMPT_RT; this patch only changes the PREEMPT_RT branch. It also predates the commit this patch fixes: alloc_empty_sheaf() has used GFP_NOWAIT in this call chain since the sheaves feature was introduced in ec66e0d59952 ("slab: add sheaf support for batching kfree_rcu() operations"), not since 2a8bb29ec9b2. It's a real question about the sheaf/barn allocation design itself, not something a small, targeted fix for the syzbot-reported splat should also try to redesign. - Same as noted for the previous review: kfree_call_rcu_nolock() is intentionally left untouched by this patch. Agreed it doesn't fully deliver on its 'any context' contract on PREEMPT_RT either, for the reasons given (local_trylock ordering, and now also alloc_empty_sheaf() reaching zone->lock). That's a separate fix. Both would be good candidates for their own patches from whoever knows the sheaf/barn allocation path best; happy to help test if one gets posted. This patch stays scoped to the specific circular-locking splat in kvfree_call_rcu() reported by syzbot. Thanks, ThangNN99