padata: always acquire cpu_hotplug_lock before pinst->lock

commit 38228e8848cd7dd86ccb90406af32de0cad24be3 upstream.

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
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/padata.c b/kernel/padata.c
index 286c5142a0f7456345c60662f1bd765148ea1cf4..6939111b3cbe08d522e8c6f623ec149653ce6fc7 100644 (file)
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -614,8 +614,8 @@ 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:
@@ -633,8 +633,8 @@ 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;
 }