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 02/21] srcutree: Suppress srcu_advance_state() mutex_lock in atomic
Date: Wed, 7 Oct 2026 13:59:05 -0700 [thread overview]
Message-ID: <20261007205924.1983367-2-paulmck@kernel.org> (raw)
In-Reply-To: <546c81a7-f677-4d8e-a304-746b227058b0@paulmck-laptop>
The new SRCU_READ_FLAVOR_ATOMIC prohibits sleeping in both readers and
grace-period waits in order to permit waiting on an SRCU grace period
within an OOM notifier. This means that srcu_advance_state() cannot
acquire ->srcu_gp_mutex in this case, because mutex_lock() can sleep.
This commit therefore adds an is_atomic parameter to srcu_advance_state().
When this parameter is false, current behavior is maintained, in other
words, ->srcu_gp_mutex is acquired and released as before. But when this
is_atomic parameter is false, the caller is responsible for excluding
other callers.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/srcutree.c | 23 +++++++++++++++--------
1 file changed, 15 insertions(+), 8 deletions(-)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index b1b3c81a72f45..c305c54a3203b 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1941,13 +1941,16 @@ EXPORT_SYMBOL_GPL(srcu_batches_completed);
/*
* Core SRCU state machine. Push state bits of ->srcu_gp_seq
* to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has
- * completed in that state.
+ * completed in that state. Set is_atomic to indicate that
+ * the caller is excluding other calls so that ->srcu_gp_mutex
+ * is not needed, and to indicate that blocking is forbidden.
*/
-static void srcu_advance_state(struct srcu_struct *ssp)
+static void srcu_advance_state(struct srcu_struct *ssp, bool is_atomic)
{
int idx;
- mutex_lock(&ssp->srcu_sup->srcu_gp_mutex);
+ if (!is_atomic)
+ mutex_lock(&ssp->srcu_sup->srcu_gp_mutex);
/*
* Because readers might be delayed for an extended period after
@@ -1965,7 +1968,8 @@ static void srcu_advance_state(struct srcu_struct *ssp)
if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) {
WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq));
raw_spin_unlock_irq_rcu_node(ssp->srcu_sup);
- mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
+ if (!is_atomic)
+ mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
return;
}
idx = rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq));
@@ -1973,7 +1977,8 @@ static void srcu_advance_state(struct srcu_struct *ssp)
srcu_gp_start(ssp);
raw_spin_unlock_irq_rcu_node(ssp->srcu_sup);
if (idx != SRCU_STATE_IDLE) {
- mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
+ if (!is_atomic)
+ mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
return; /* Someone else started the grace period. */
}
}
@@ -1981,7 +1986,8 @@ static void srcu_advance_state(struct srcu_struct *ssp)
if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
idx = !(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]);
if (!try_check_zero(ssp, idx, 1)) {
- mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
+ if (!is_atomic)
+ mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
return; /* readers present, retry later. */
}
srcu_flip(ssp);
@@ -1999,7 +2005,8 @@ static void srcu_advance_state(struct srcu_struct *ssp)
*/
idx = !(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]);
if (!try_check_zero(ssp, idx, 2)) {
- mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
+ if (!is_atomic)
+ mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
return; /* readers present, retry later. */
}
ssp->srcu_sup->srcu_n_exp_nodelay = 0;
@@ -2107,7 +2114,7 @@ static void process_srcu(struct work_struct *work)
sup = container_of(work, struct srcu_usage, work.work);
ssp = sup->srcu_ssp;
- srcu_advance_state(ssp);
+ srcu_advance_state(ssp, false);
raw_spin_lock_irq_rcu_node(ssp->srcu_sup);
curdelay = srcu_get_delay(ssp);
raw_spin_unlock_irq_rcu_node(ssp->srcu_sup);
--
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 ` Paul E. McKenney [this message]
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 ` [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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