From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com,
rostedt@goodmis.org, "Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH v2 07/21] srcutree: Disable preemption across synchronize_srcu_atomic()
Date: Wed, 7 Oct 2026 13:59:10 -0700 [thread overview]
Message-ID: <20261007205924.1983367-7-paulmck@kernel.org> (raw)
In-Reply-To: <546c81a7-f677-4d8e-a304-746b227058b0@paulmck-laptop>
Because synchronize_srcu_atomic() cannot sleep, if a pair of them run
concurrently pinned to the same CPU, it is possible that one will spin
uselessly waiting for the other while at the same time preventing that
other from running. This commit therefore disables preemption to prevent
this failure mode.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/srcutree.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 7ff45e992c011..672fb41345c91 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -2123,11 +2123,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
// Perhaps others will do our work for us.
srcu_state = get_state_synchronize_srcu(ssp);
+ preempt_disable();
while (atomic_read(&sup->srcu_atomic_gp_flag) ||
atomic_xchg(&sup->srcu_atomic_gp_flag, 1)) {
+ preempt_enable();
if (poll_state_synchronize_srcu(ssp, srcu_state))
return;
cpu_relax();
+ preempt_disable();
}
// One last check for others doing our work for us under the lock.
@@ -2135,6 +2138,7 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
if (poll_state_synchronize_srcu(ssp, srcu_state)) {
raw_spin_unlock_irq_rcu_node(sup);
atomic_set(&sup->srcu_atomic_gp_flag, 0);
+ preempt_enable();
return;
}
@@ -2152,6 +2156,7 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
}
ASSERT_EXCLUSIVE_WRITER(sup->srcu_atomic_gp_flag);
atomic_set_release(&sup->srcu_atomic_gp_flag, 0);
+ preempt_enable();
non_block_end();
}
EXPORT_SYMBOL_GPL(synchronize_srcu_atomic);
--
2.40.1
next prev parent reply other threads:[~2026-10-07 20:59 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-07 20:59 [PATCH v2 0/21] Add atomic SRCU &c for v7.4 Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 01/21] srcutiny: Make a Tiny SRCU grace period imply an RCU grace period Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 02/21] srcutree: Suppress srcu_advance_state() mutex_lock in atomic Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 03/21] srcutree: Suppress to-big transition for atomic SRCU Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 04/21] srcutree: Add an atomic Tree SRCU Paul E. McKenney
2026-10-08 7:39 ` David Woodhouse
2026-10-08 15:51 ` Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 05/21] srcutiny: Add an atomic Tiny SRCU Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 06/21] rcutorture: Add support for testing synchronize_srcu_atomic() Paul E. McKenney
2026-10-07 20:59 ` Paul E. McKenney [this message]
2026-10-07 20:59 ` [PATCH v2 08/21] srcu: Use IRQ_WORK_INIT_HARD for srcu's irq_work Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 09/21] srcutree: Warn if Tiny SRCU readers are preempted Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 10/21] srcutree: Explicitly note DEFINE_SRCU() needs for srcu_barrier() Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 11/21] rcutorture: Add atomic-SRCU support to torture.sh Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 12/21] srcutree: Add reader-free fastpath to synchronize_srcu_atomic() Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 13/21] srcutree: Skip callback scheduling for atomic SRCU grace periods Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 14/21] srcutree: Remove srcu_barrier() sleep for atomic SRCU Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 15/21] srcu: Restrict atomic-SRCU non_block annotation to task context Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 16/21] srcutree: Make init_srcu_struct_atomic() prevent transition to big Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 17/21] srcutree: Don't transition atomic SRCU to big in srcu_gp_end() Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 18/21] srcutree: Skip torture to-big transition for atomic SRCU Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 19/21] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic() Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 20/21] srcutiny: " Paul E. McKenney
2026-10-07 20:59 ` [PATCH v2 21/21] srcutree: Preserve IRQ state in synchronize_srcu_atomic() callchain Paul E. McKenney
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