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Mon, 07 Sep 2026 00:59:11 -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 08/13] srcutree: Forbid srcu_expedite_current() on atomic SRCU Date: Mon, 7 Sep 2026 15:58:24 +0800 Message-ID: <20260907075829.2073224-9-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 srcu_expedite_current() has no early guard for atomic SRCU, so calling it on an atomic srcu_struct leaks the expediting callback in __call_srcu(), leaving ->srcu_ec_state stuck at SRCU_EC_PENDING. Add the same WARN_ON_ONCE()-guarded early return used by the other forbidden APIs, and list srcu_expedite_current() and srcu_barrier() in synchronize_srcu_atomic()'s documentation. Signed-off-by: Kunwu Chan --- kernel/rcu/srcutree.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 74acd5645d4c..2d2a12f86115 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1972,6 +1972,9 @@ static void srcu_expedite_current_cb(struct rcu_head *rhp) * no current grace period, one might be created. If the current grace * period is currently sleeping, that sleep will complete before expediting * will take effect. + * + * This function must not be invoked on srcu_struct structures that are + * used with srcu_read_lock_atomic() and synchronize_srcu_atomic(). */ void srcu_expedite_current(struct srcu_struct *ssp) { @@ -1979,6 +1982,9 @@ void srcu_expedite_current(struct srcu_struct *ssp) bool needcb = false; struct srcu_data *sdp; + // Atomic SRCU has no callbacks, so there is nothing to expedite. + if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC)) + return; migrate_disable(); sdp = this_cpu_ptr(ssp->sda); raw_spin_lock_irqsave_sdp_contention(sdp, &flags); @@ -2104,8 +2110,9 @@ static void srcu_advance_state(struct srcu_struct *ssp, bool is_atomic) * * If synchronize_srcu_atomic() is invoked on a given srcu_struct * structure, then none of call_srcu(), synchronize_srcu(), - * synchronize_srcu_expedited(), or start_poll_synchronize_srcu() may be - * invoked on that same structure. + * synchronize_srcu_expedited(), start_poll_synchronize_srcu(), + * srcu_barrier(), or srcu_expedite_current() may be invoked on that + * same structure. * * Because synchronize_srcu_atomic() is even more expedited than is * synchronize_srcu_expedited(), there is no expedited counterpart to -- 2.43.0