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 09/21] srcutree: Warn if Tiny SRCU readers are preempted
Date: Wed, 7 Oct 2026 13:59:12 -0700 [thread overview]
Message-ID: <20261007205924.1983367-9-paulmck@kernel.org> (raw)
In-Reply-To: <546c81a7-f677-4d8e-a304-746b227058b0@paulmck-laptop>
The fastpath of synchronize_srcu_atomic() should always be taken
because readers always disable preemption. Therefore, the fact that
synchronize_srcu_atomic() is running at all should mean that all readers
have ended.
But there are always bugs. And responding to a usage bug with a
too-short SRCU grace period, and thus possibly corrupting memory
is at best a sadistic response so such a bug. For this reason,
synchronize_srcu_atomic() explicitly waits for readers. Except that
it does so silently, possibly failing to flag this bug. This commit
therefore adds a splat if synchronize_srcu_atomic() fails to take the
early exit.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/srcutiny.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 08e089e3e969e..a31398def0b18 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -375,6 +375,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
return;
}
+ // Because readers disable preemption, we should never get here.
+ // However, a splat and some spinning is usually preferable to
+ // memory corruption due to a too-short grace period. There is
+ // the possibility that this will hang if the preempted reader is
+ // not looked upon favorably by the scheduler, but this is still
+ // preferable to memory corruption.
+ WARN_ON_ONCE(1);
+
// Wait to drive a grace period or for someone else to do it
// for us while we are lazily preempted.
while (ssp->srcu_atomic_gp_flag) {
--
2.40.1
next prev parent reply other threads:[~2026-10-07 20:59 UTC|newest]
Thread overview: 22+ 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
2026-10-07 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 ` [PATCH v2 07/21] srcutree: Disable preemption across synchronize_srcu_atomic() Paul E. McKenney
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 ` Paul E. McKenney [this message]
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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