[PATCH 6.6 088/105] padata: Reset next CPU when reorder sequence wraps around

Greg Kroah-Hartman
2025-10-21T19:56:52Z

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>
[ relocated fix from padata_reorder() function to padata_find_next() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/padata.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -290,7 +290,11 @@ static struct padata_priv *padata_find_n
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);