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* [PATCH 4.19 85/87] padata: always acquire cpu_hotplug_lock before pinst->lock
       [not found] <20200303174349.075101355@linuxfoundation.org>
@ 2020-03-03 17:44 ` Greg Kroah-Hartman
  0 siblings, 0 replies; only message in thread
From: Greg Kroah-Hartman @ 2020-03-03 17:44 UTC (permalink / raw)
  To: linux-kernel
  Cc: Greg Kroah-Hartman, stable, Daniel Jordan, Eric Biggers,
	Herbert Xu, Steffen Klassert, linux-crypto

From: Daniel Jordan <daniel.m.jordan@oracle.com>

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>

---
 kernel/padata.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -671,8 +671,8 @@ int padata_set_cpumask(struct padata_ins
 	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:
@@ -690,8 +690,8 @@ int padata_set_cpumask(struct padata_ins
 	err =  __padata_set_cpumasks(pinst, parallel_mask, serial_mask);
 
 out:
-	put_online_cpus();
 	mutex_unlock(&pinst->lock);
+	put_online_cpus();
 
 	return err;
 }



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