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Subject[PATCH v2 2/5] padata: always acquire cpu_hotplug_lock before pinst->lock
Date
lockdep complains when padata's paths to update cpumasks via CPU hotplug
and sysfs are both taken:

# echo 0 > /sys/devices/system/cpu/cpu1/online
# echo ff > /sys/kernel/pcrypt/pencrypt/parallel_cpumask

======================================================
WARNING: possible circular locking dependency detected
5.4.0-rc8-padata-cpuhp-v3+ #1 Not tainted
------------------------------------------------------
bash/205 is trying to acquire lock:
ffffffff8286bcd0 (cpu_hotplug_lock.rw_sem){++++}, at: padata_set_cpumask+0x2b/0x120

but task is already holding lock:
ffff8880001abfa0 (&pinst->lock){+.+.}, at: padata_set_cpumask+0x26/0x120

which lock already depends on the new lock.

padata doesn't take cpu_hotplug_lock and pinst->lock in a consistent
order. Which should be first? CPU hotplug calls into padata with
cpu_hotplug_lock already held, so it should have priority.

Fixes: 6751fb3c0e0c ("padata: Use get_online_cpus/put_online_cpus")
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
kernel/padata.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index a2fa6223e1a0..2f8db63aefc4 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -643,8 +643,8 @@ int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
struct cpumask *serial_mask, *parallel_mask;
int err = -EINVAL;

- mutex_lock(&pinst->lock);
get_online_cpus();
+ mutex_lock(&pinst->lock);

switch (cpumask_type) {
case PADATA_CPU_PARALLEL:
@@ -662,8 +662,8 @@ int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
err = __padata_set_cpumasks(pinst, parallel_mask, serial_mask);

out:
- put_online_cpus();
mutex_unlock(&pinst->lock);
+ put_online_cpus();

return err;
}
--
2.24.0
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