6.12-stable patches

added patches:
	sched-fair-block-delayed-tasks-on-throttled-hierarchy-during-dequeue.patch

diff --git a/queue-6.12/sched-fair-block-delayed-tasks-on-throttled-hierarchy-during-dequeue.patch b/queue-6.12/sched-fair-block-delayed-tasks-on-throttled-hierarchy-during-dequeue.patch
new file mode 100644 (file)
index 0000000..d530886
--- /dev/null
+++ b/queue-6.12/sched-fair-block-delayed-tasks-on-throttled-hierarchy-during-dequeue.patch
@@ -0,0 +1,96 @@
+From kprateek.nayak@amd.com  Fri Oct 17 15:25:45 2025
+From: K Prateek Nayak <kprateek.nayak@amd.com>
+Date: Wed, 15 Oct 2025 06:03:59 +0000
+Subject: sched/fair: Block delayed tasks on throttled hierarchy during dequeue
+To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Sasha Levin <sashal@kernel.org>, <stable@vger.kernel.org>, Matt Fleming <matt@readmodwrite.com>, Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>, Vincent Guittot <vincent.guittot@linaro.org>, <linux-kernel@vger.kernel.org>
+Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>, Steven Rostedt <rostedt@goodmis.org>, Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>, Valentin Schneider <vschneid@redhat.com>, <kernel-team@cloudflare.com>, Matt Fleming <mfleming@cloudflare.com>, "Oleg Nesterov" <oleg@redhat.com>, John Stultz <jstultz@google.com>, Chris Arges <carges@cloudflare.com>, K Prateek Nayak <kprateek.nayak@amd.com>
+Message-ID: <20251015060359.34722-1-kprateek.nayak@amd.com>
+
+From: K Prateek Nayak <kprateek.nayak@amd.com>
+
+Dequeuing a fair task on a throttled hierarchy returns early on
+encountering a throttled cfs_rq since the throttle path has already
+dequeued the hierarchy above and has adjusted the h_nr_* accounting till
+the root cfs_rq.
+
+dequeue_entities() crucially misses calling __block_task() for delayed
+tasks being dequeued on the throttled hierarchies, but this was mostly
+harmless until commit b7ca5743a260 ("sched/core: Tweak
+wait_task_inactive() to force dequeue sched_delayed tasks") since all
+existing cases would re-enqueue the task if task_on_rq_queued() returned
+true and the task would eventually be blocked at pick after the
+hierarchy was unthrottled.
+
+wait_task_inactive() is special as it expects the delayed task on
+throttled hierarchy to reach the blocked state on dequeue but since
+__block_task() is never called, task_on_rq_queued() continues to return
+true. Furthermore, since the task is now off the hierarchy, the pick
+never reaches it to fully block the task even after unthrottle leading
+to wait_task_inactive() looping endlessly.
+
+Remedy this by calling __block_task() if a delayed task is being
+dequeued on a throttled hierarchy.
+
+This fix is only required for stabled kernels implementing delay dequeue
+(>= v6.12) before v6.18 since upstream commit e1fad12dcb66 ("sched/fair:
+Switch to task based throttle model") indirectly fixes this by removing
+the early return conditions in dequeue_entities() as part of the per-task
+throttle feature.
+
+Cc: stable@vger.kernel.org
+Reported-by: Matt Fleming <matt@readmodwrite.com>
+Closes: https://lore.kernel.org/all/20250925133310.1843863-1-matt@readmodwrite.com/
+Fixes: b7ca5743a260 ("sched/core: Tweak wait_task_inactive() to force dequeue sched_delayed tasks")
+Tested-by: Matt Fleming <mfleming@cloudflare.com>
+Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ kernel/sched/fair.c |    9 ++++++---
+ 1 file changed, 6 insertions(+), 3 deletions(-)
+
+--- a/kernel/sched/fair.c
++++ b/kernel/sched/fair.c
+@@ -7187,6 +7187,7 @@ static int dequeue_entities(struct rq *r
+       int h_nr_delayed = 0;
+       struct cfs_rq *cfs_rq;
+       u64 slice = 0;
++      int ret = 0;
+ 
+       if (entity_is_task(se)) {
+               p = task_of(se);
+@@ -7218,7 +7219,7 @@ static int dequeue_entities(struct rq *r
+ 
+               /* end evaluation on encountering a throttled cfs_rq */
+               if (cfs_rq_throttled(cfs_rq))
+-                      return 0;
++                      goto out;
+ 
+               /* Don't dequeue parent if it has other entities besides us */
+               if (cfs_rq->load.weight) {
+@@ -7261,7 +7262,7 @@ static int dequeue_entities(struct rq *r
+ 
+               /* end evaluation on encountering a throttled cfs_rq */
+               if (cfs_rq_throttled(cfs_rq))
+-                      return 0;
++                      goto out;
+       }
+ 
+       sub_nr_running(rq, h_nr_queued);
+@@ -7273,6 +7274,8 @@ static int dequeue_entities(struct rq *r
+       if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
+               rq->next_balance = jiffies;
+ 
++      ret = 1;
++out:
+       if (p && task_delayed) {
+               SCHED_WARN_ON(!task_sleep);
+               SCHED_WARN_ON(p->on_rq != 1);
+@@ -7288,7 +7291,7 @@ static int dequeue_entities(struct rq *r
+               __block_task(rq, p);
+       }
+ 
+-      return 1;
++      return ret;
+ }
+ 
+ /*

diff --git a/queue-6.12/series b/queue-6.12/series
index 951af66de6d4581c563a4e92039b8aea9bfb6554..5bc91f66becab61bad4f36a3e5fa90e1406f62c1 100644 (file)
--- a/queue-6.12/series
+++ b/queue-6.12/series
@@ -270,3 +270,4 @@ fs-add-initramfs_options-to-set-initramfs-mount-opti.patch
 cramfs-verify-inode-mode-when-loading-from-disk.patch
 writeback-avoid-softlockup-when-switching-many-inode.patch
 writeback-avoid-excessively-long-inode-switching-tim.patch
+sched-fair-block-delayed-tasks-on-throttled-hierarchy-during-dequeue.patch