FAILED: patch "[PATCH] padata: Reset next CPU when reorder sequence wraps around" failed to apply to 5.10-stable tree

FAILED: patch "[PATCH] padata: Reset next CPU when reorder sequence wraps around" failed to apply to 5.10-stable tree

[gregkh]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 501302d5cee0d8e8ec2c4a5919c37e0df9abc99b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025101651-sizing-subfloor-8c1d@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 501302d5cee0d8e8ec2c4a5919c37e0df9abc99b Mon Sep 17 00:00:00 2001
From: Xiao Liang <shaw.leon@gmail.com>
Date: Sun, 17 Aug 2025 00:30:15 +0800
Subject: [PATCH] padata: Reset next CPU when reorder sequence wraps around

When seq_nr wraps around, the next reorder job with seq 0 is hashed to
the first CPU in padata_do_serial(). Correspondingly, need reset pd->cpu
to the first one when pd->processed wraps around. Otherwise, if the
number of used CPUs is not a power of 2, padata_find_next() will be
checking a wrong list, hence deadlock.

Fixes: 6fc4dbcf0276 ("padata: Replace delayed timer with immediate workqueue in padata_reorder")
Cc: <stable@vger.kernel.org>
Signed-off-by: Xiao Liang <shaw.leon@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/kernel/padata.c b/kernel/padata.c
index f85f8bd788d0..833740d75483 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -291,8 +291,12 @@ static void padata_reorder(struct padata_priv *padata)
 		struct padata_serial_queue *squeue;
 		int cb_cpu;
 
-		cpu = cpumask_next_wrap(cpu, pd->cpumask.pcpu);
 		processed++;
+		/* When sequence wraps around, reset to the first CPU. */
+		if (unlikely(processed == 0))
+			cpu = cpumask_first(pd->cpumask.pcpu);
+		else
+			cpu = cpumask_next_wrap(cpu, pd->cpumask.pcpu);
 
 		cb_cpu = padata->cb_cpu;
 		squeue = per_cpu_ptr(pd->squeue, cb_cpu);

[PATCH 5.10.y] padata: Reset next CPU when reorder sequence wraps around

[Sasha Levin]

From: Xiao Liang <shaw.leon@gmail.com>

[ Upstream commit 501302d5cee0d8e8ec2c4a5919c37e0df9abc99b ]

When seq_nr wraps around, the next reorder job with seq 0 is hashed to
the first CPU in padata_do_serial(). Correspondingly, need reset pd->cpu
to the first one when pd->processed wraps around. Otherwise, if the
number of used CPUs is not a power of 2, padata_find_next() will be
checking a wrong list, hence deadlock.

Fixes: 6fc4dbcf0276 ("padata: Replace delayed timer with immediate workqueue in padata_reorder")
Cc: <stable@vger.kernel.org>
Signed-off-by: Xiao Liang <shaw.leon@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
[ moved from padata_reorder() local variables to padata_find_next() using pd->processed and pd->cpu struct members ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/padata.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index 1bd61add09158..6c8a141b5c4b2 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -295,7 +295,11 @@ static struct padata_priv *padata_find_next(struct parallel_data *pd,
 	if (remove_object) {
 		list_del_init(&padata->list);
 		++pd->processed;
-		pd->cpu = cpumask_next_wrap(cpu, pd->cpumask.pcpu, -1, false);
+		/* When sequence wraps around, reset to the first CPU. */
+		if (unlikely(pd->processed == 0))
+			pd->cpu = cpumask_first(pd->cpumask.pcpu);
+		else
+			pd->cpu = cpumask_next_wrap(cpu, pd->cpumask.pcpu, -1, false);
 	}
 
 	spin_unlock(&reorder->lock);
-- 
2.51.0