This is a note to let you know that I've just added the patch titled
rcu-tasks: Simplify trc_read_check_handler() atomic operations
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-tasks-simplify-trc_read_check_handler-atomic-operations.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From stable-owner@xxxxxxxxxxxxxxx Sat Jul 15 02:47:26 2023
From: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>
Date: Sat, 15 Jul 2023 00:47:11 +0000
Subject: rcu-tasks: Simplify trc_read_check_handler() atomic operations
To: stable@xxxxxxxxxxxxxxx
Cc: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>, "Paul E . McKenney" <paulmck@xxxxxxxxxx>
Message-ID: <20230715004711.2938489-4-joel@xxxxxxxxxxxxxxxxx>
From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
[ Upstream commit 96017bf9039763a2e02dcc6adaa18592cd73a39d ]
Currently, trc_wait_for_one_reader() atomically increments
the trc_n_readers_need_end counter before sending the IPI
invoking trc_read_check_handler(). All failure paths out of
trc_read_check_handler() and also from the smp_call_function_single()
within trc_wait_for_one_reader() must carefully atomically decrement
this counter. This is more complex than it needs to be.
This commit therefore simplifies things and saves a few lines of
code by dispensing with the atomic decrements in favor of having
trc_read_check_handler() do the atomic increment only in the success case.
In theory, this represents no change in functionality.
Cc: <stable@xxxxxxxxxxxxxxx> # 5.10.x
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tasks.h | 20 +++-----------------
1 file changed, 3 insertions(+), 17 deletions(-)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -841,32 +841,24 @@ static void trc_read_check_handler(void
// If the task is no longer running on this CPU, leave.
if (unlikely(texp != t)) {
- if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))
- wake_up(&trc_wait);
goto reset_ipi; // Already on holdout list, so will check later.
}
// If the task is not in a read-side critical section, and
// if this is the last reader, awaken the grace-period kthread.
if (likely(!READ_ONCE(t->trc_reader_nesting))) {
- if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))
- wake_up(&trc_wait);
- // Mark as checked after decrement to avoid false
- // positives on the above WARN_ON_ONCE().
WRITE_ONCE(t->trc_reader_checked, true);
goto reset_ipi;
}
// If we are racing with an rcu_read_unlock_trace(), try again later.
- if (unlikely(READ_ONCE(t->trc_reader_nesting) < 0)) {
- if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))
- wake_up(&trc_wait);
+ if (unlikely(READ_ONCE(t->trc_reader_nesting) < 0))
goto reset_ipi;
- }
WRITE_ONCE(t->trc_reader_checked, true);
// Get here if the task is in a read-side critical section. Set
// its state so that it will awaken the grace-period kthread upon
// exit from that critical section.
+ atomic_inc(&trc_n_readers_need_end); // One more to wait on.
WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs));
WRITE_ONCE(t->trc_reader_special.b.need_qs, true);
@@ -960,21 +952,15 @@ static void trc_wait_for_one_reader(stru
if (per_cpu(trc_ipi_to_cpu, cpu) || t->trc_ipi_to_cpu >= 0)
return;
- atomic_inc(&trc_n_readers_need_end);
per_cpu(trc_ipi_to_cpu, cpu) = true;
t->trc_ipi_to_cpu = cpu;
rcu_tasks_trace.n_ipis++;
- if (smp_call_function_single(cpu,
- trc_read_check_handler, t, 0)) {
+ if (smp_call_function_single(cpu, trc_read_check_handler, t, 0)) {
// Just in case there is some other reason for
// failure than the target CPU being offline.
rcu_tasks_trace.n_ipis_fails++;
per_cpu(trc_ipi_to_cpu, cpu) = false;
t->trc_ipi_to_cpu = cpu;
- if (atomic_dec_and_test(&trc_n_readers_need_end)) {
- WARN_ON_ONCE(1);
- wake_up(&trc_wait);
- }
}
}
}
Patches currently in stable-queue which might be from stable-owner@xxxxxxxxxxxxxxx are
queue-5.10/rcu-tasks-simplify-trc_read_check_handler-atomic-operations.patch
queue-5.10/netfilter-nf_tables-fix-chain-binding-transaction-logic.patch
queue-5.10/netfilter-nf_tables-drop-map-element-references-from-preparation-phase.patch
queue-5.10/netfilter-nf_tables-fix-scheduling-while-atomic-splat.patch
queue-5.10/netfilter-nf_tables-reject-unbound-anonymous-set-before-commit-phase.patch
queue-5.10/netfilter-nf_tables-use-net_generic-infra-for-transaction-data.patch
queue-5.10/netfilter-nftables-rename-set-element-data-activation-deactivation-functions.patch
queue-5.10/netfilter-nf_tables-incorrect-error-path-handling-with-nft_msg_newrule.patch
queue-5.10/rcu-tasks-mark-trc_reader_nesting-data-races.patch
queue-5.10/netfilter-nf_tables-reject-unbound-chain-set-before-commit-phase.patch
queue-5.10/rcu-tasks-mark-trc_reader_special.b.need_qs-data-races.patch
queue-5.10/netfilter-nf_tables-add-rescheduling-points-during-loop-detection-walks.patch
queue-5.10/netfilter-nf_tables-add-nft_trans_prepare_error-to-deal-with-bound-set-chain.patch
queue-5.10/netfilter-nf_tables-unbind-non-anonymous-set-if-rule-construction-fails.patch
