Commit 38228e88 authored Dec 03, 2019 by Daniel Jordan Committed by Herbert Xu Dec 11, 2019

padata: always acquire cpu_hotplug_lock before pinst->lock



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: 6751fb3c ("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>

parent 894c9ef9

kernel/padata.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

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