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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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