linux-kernel - [PATCH v2 4/5] padata: always acquire cpu_hotplug

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Message-Id: <20190828221425.22701-5-daniel.m.jordan@oracle.com>
Date:   Wed, 28 Aug 2019 18:14:24 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        Steffen Klassert <steffen.klassert@...unet.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: [PATCH v2 4/5] padata: always acquire cpu_hotplug_lock before pinst->lock

lockdep complains when...

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

  ======================================================
  WARNING: possible circular locking dependency detected
  5.3.0-rc5-padata-base+ #6 Not tainted
  ------------------------------------------------------
  bash/258 is trying to acquire lock:
  00000000c43f7f29 (cpu_hotplug_lock.rw_sem){++++}, at: padata_set_cpumask+0x30/0x130

  but task is already holding lock:
  00000000676aa31d (&pinst->lock){+.+.}, at: padata_set_cpumask+0x2b/0x130

  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@...cle.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-crypto@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 kernel/padata.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index 6adce3b203fe..75e668fedd8d 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -603,8 +603,8 @@ 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:
@@ -622,8 +622,8 @@ 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;
 }
-- 
2.23.0