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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 2470920006 X-Stat-Signature: in86p3concogr7p8dw4k9o4fm5oppbp7 X-HE-Tag: 1788184553-479451 X-HE-Meta: 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 y3J4NTnc 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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