From: Xiao Liang <shaw.leon@gmail.com>
Date: Mon, 20 Oct 2025 15:39:11 +0000 (-0400)
Subject: padata: Reset next CPU when reorder sequence wraps around
X-Git-Tag: v6.1.158~34
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ca2bfa1500b0fa6105fd3181877f9fa3d867346d;p=thirdparty%2Fkernel%2Fstable.git

padata: Reset next CPU when reorder sequence wraps around

[ 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>
[ applied fix in padata_find_next() instead of padata_reorder() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/kernel/padata.c b/kernel/padata.c
index b3f79f23060c1..d49f97abe086f 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -282,7 +282,11 @@ 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);