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Mon, 07 Sep 2026 00:59:08 -0700 (PDT) From: Kunwu Chan X-Google-Original-From: Kunwu Chan To: paulmck@kernel.org, jiangshanlai@gmail.com, josh@joshtriplett.org Cc: rostedt@goodmis.org, mathieu.desnoyers@efficios.com, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, Kunwu Chan Subject: [PATCH 07/13] srcutree: Don't transition atomic SRCU to big in srcu_gp_end() Date: Mon, 7 Sep 2026 15:58:23 +0800 Message-ID: <20260907075829.2073224-8-kunwu.chan@linux.dev> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260907075829.2073224-1-kunwu.chan@linux.dev> References: <20260907075829.2073224-1-kunwu.chan@linux.dev> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Kunwu Chan The transition-to-big code path in srcu_gp_end() calls init_srcu_struct_nodes() with GFP_KERNEL, which is illegal in the atomic context reachable from synchronize_srcu_atomic(). Atomic SRCU has no use for the srcu_node combining tree: it has neither callbacks nor srcu_barrier() operations, and its grace periods are serialized by ->srcu_atomic_gp_flag instead. Skip this transition entirely for atomic SRCU, which is also defense in depth against any path that might wrongly set ->srcu_size_state for an atomic srcu_struct. Signed-off-by: Kunwu Chan --- kernel/rcu/srcutree.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 01f224a56b41..74acd5645d4c 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1074,8 +1074,9 @@ static void srcu_gp_end(struct srcu_struct *ssp, bool is_atomic) raw_spin_unlock_irq_rcu_node(sup); } - /* Transition to big if needed. */ - if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) { + /* Transition to big if needed, but never for atomic SRCU. */ + if (!is_atomic && ss_state != SRCU_SIZE_SMALL && + ss_state != SRCU_SIZE_BIG) { if (ss_state == SRCU_SIZE_ALLOC) init_srcu_struct_nodes(ssp, GFP_KERNEL); else -- 2.43.0