linux-kernel - [PATCH] padata: Reset next CPU when reorder sequence wraps around

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Message-ID: <20250715062401.172642-1-shaw.leon@gmail.com>
Date: Tue, 15 Jul 2025 14:23:57 +0800
From: Xiao Liang <shaw.leon@...il.com>
To: Steffen Klassert <steffen.klassert@...unet.com>,
	Daniel Jordan <daniel.m.jordan@...cle.com>,
	Herbert Xu <herbert@...dor.apana.org.au>
Cc: linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org
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")
Signed-off-by: Xiao Liang <shaw.leon@...il.com>
---
 kernel/padata.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index 7eee94166357..ebb52c6db637 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -290,7 +290,11 @@ 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);
+		/* 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);
 	}
 
 	spin_unlock(&reorder->lock);
-- 
2.50.0