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([2405:4802:21dc:72d0:e0c:d445:c26f:9091]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d75963bc14sm29404725ad.32.2026.08.30.23.33.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Aug 2026 23:33:50 -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 Subject: Re: [PATCH v2] mm/slab: don't use kfree_rcu sheaves on PREEMPT_RT in kvfree_call_rcu() Date: Mon, 31 Aug 2026 13:33:44 +0700 Message-ID: <20260831063344.7933-1-ngocthang2710.1999@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260831062054.319EA1F000E9@smtp.kernel.org> References: <20260831062054.319EA1F000E9@smtp.kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: C29F7C0002 X-Stat-Signature: w3t9u7aqu9jqsrzint8t3zjxxhki7m64 X-HE-Tag: 1788158033-697897 X-HE-Meta: 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 JRjACfHJ 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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 flagged items are pre-existing and out of scope for this patch: - The headless kvfree_rcu(ptr) might_sleep()/synchronize_rcu() path is never reached by the caller this patch fixes: set_cpus_allowed_force() uses the headed two-argument kfree_rcu(ptr, rcu) form specifically to avoid it (see its own comment), so it's unrelated to the sheaf-bypass this patch adds. - kfree_call_rcu_nolock() still hitting local_trylock(&s->cpu_sheaves->lock) unconditionally is exactly what this patch's commit message already calls out as unsafe under a raw spinlock. This patch intentionally leaves kfree_call_rcu_nolock() untouched; fixing its 'any context' guarantee belongs in a separate patch. This patch stays scoped to the specific syzbot-reported splat in kvfree_call_rcu(). Happy to look at the two pre-existing issues separately if a maintainer wants a follow-up patch for either. Thanks, ThangNN99