From: Xiao Liang <shaw.leon@gmail.com>
Date: Sat, 16 Aug 2025 16:30:15 +0000 (+0800)
Subject: padata: Reset next CPU when reorder sequence wraps around
X-Git-Tag: v6.18-rc1~84^2~60
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=501302d5cee0d8e8ec2c4a5919c37e0df9abc99b;p=thirdparty%2Fkernel%2Fstable.git

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 f85f8bd788d0d..833740d754837 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);