linux-kernel - [tip:smp/hotplug] padata: Avoid nested calls to get_online_cpus() in pcrypt_init

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Date:   Thu, 20 Apr 2017 04:20:23 -0700
From:   tip-bot for Sebastian Andrzej Siewior <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     steffen.klassert@...unet.com, bigeasy@...utronix.de,
        rostedt@...dmis.org, hpa@...or.com, tglx@...utronix.de,
        peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip:smp/hotplug] padata: Avoid nested calls to get_online_cpus()
 in pcrypt_init_padata()

Commit-ID:  bbd8797975ce0191ac72d575f7e34033b5a5f620
Gitweb:     http://git.kernel.org/tip/bbd8797975ce0191ac72d575f7e34033b5a5f620
Author:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate: Tue, 18 Apr 2017 19:04:46 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 20 Apr 2017 13:08:51 +0200

padata: Avoid nested calls to get_online_cpus() in pcrypt_init_padata()

pcrypt_init_padata()
   get_online_cpus()
   padata_alloc_possible()
     padata_alloc()
       get_online_cpus()

The nested call to get_online_cpus() works with the current implementation,
but prevents the conversion to a percpu rwsem.

The other caller of padata_alloc_possible() is pcrypt_init_padata() which
calls from a get_online_cpus() protected region as well.

Remove the get_online_cpus() call in padata_alloc() and document the
calling convention.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Steffen Klassert <steffen.klassert@...unet.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-crypto@...r.kernel.org
Link: http://lkml.kernel.org/r/20170418170552.697398655@linutronix.de

---
 kernel/padata.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index 18992bf..e5ff511 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -945,6 +945,8 @@ static struct kobj_type padata_attr_type = {
  * @wq: workqueue to use for the allocated padata instance
  * @pcpumask: cpumask that will be used for padata parallelization
  * @cbcpumask: cpumask that will be used for padata serialization
+ *
+ * Must be called from a get_online_cpus() protected region
  */
 static struct padata_instance *padata_alloc(struct workqueue_struct *wq,
 					    const struct cpumask *pcpumask,
@@ -957,7 +959,6 @@ static struct padata_instance *padata_alloc(struct workqueue_struct *wq,
 	if (!pinst)
 		goto err;
 
-	get_online_cpus();
 	if (!alloc_cpumask_var(&pinst->cpumask.pcpu, GFP_KERNEL))
 		goto err_free_inst;
 	if (!alloc_cpumask_var(&pinst->cpumask.cbcpu, GFP_KERNEL)) {
@@ -997,7 +998,6 @@ err_free_masks:
 	free_cpumask_var(pinst->cpumask.cbcpu);
 err_free_inst:
 	kfree(pinst);
-	put_online_cpus();
 err:
 	return NULL;
 }
@@ -1008,6 +1008,8 @@ err:
  *                         parallel workers.
  *
  * @wq: workqueue to use for the allocated padata instance
+ *
+ * Must be called from a get_online_cpus() protected region
  */
 struct padata_instance *padata_alloc_possible(struct workqueue_struct *wq)
 {