[5.4,113/344] padata: always acquire cpu_hotplug_lock before pinst->lock

Commit Message

Greg KH Feb. 21, 2020, 7:38 a.m. UTC

From: Daniel Jordan <[e-mail]>

[ Upstream commit 38228e8848cd7dd86ccb90406af32de0cad24be3 ]

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 <[e-mail]>
Cc: Eric Biggers <[e-mail]>
Cc: Herbert Xu <[e-mail]>
Cc: Steffen Klassert <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Herbert Xu <[e-mail]>
Signed-off-by: Sasha Levin <[e-mail]>
---
 kernel/padata.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Patch

diff --git a/kernel/padata.c b/kernel/padata.c
index fda7a7039422d..fdbbe96547713 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;
 }