[RFC 6/9] padata, pcrypt: take CPU hotplug lock internally in padata_alloc_possible

[Daniel Jordan]

With pcrypt's cpumask no longer used, take the CPU hotplug lock inside
padata_alloc_possible.

Useful later in the series for avoiding nested acquisition of the CPU
hotplug lock in padata when padata_alloc_possible is allocating an
unbound workqueue.

Without this patch, this nested acquisition would happen later in the
series:

      pcrypt_init_padata
        get_online_cpus
        alloc_padata_possible
          alloc_padata
            alloc_workqueue(WQ_UNBOUND)   // later in the series
              alloc_and_link_pwqs
                apply_wqattrs_lock
                  get_online_cpus         // recursive rwsem acquisition

Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
 crypto/pcrypt.c |  4 ----
 kernel/padata.c | 17 +++++++++--------
 2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/crypto/pcrypt.c b/crypto/pcrypt.c
index 2ec36e6a132f..543792e0ebf0 100644
--- a/crypto/pcrypt.c
+++ b/crypto/pcrypt.c
@@ -308,8 +308,6 @@ static int pcrypt_init_padata(struct padata_instance **pinst, const char *name)
 {
 	int ret = -ENOMEM;
 
-	get_online_cpus();
-
 	*pinst = padata_alloc_possible(name);
 	if (!*pinst)
 		return ret;
@@ -318,8 +316,6 @@ static int pcrypt_init_padata(struct padata_instance **pinst, const char *name)
 	if (ret)
 		padata_free(*pinst);
 
-	put_online_cpus();
-
 	return ret;
 }
 
diff --git a/kernel/padata.c b/kernel/padata.c
index 9d9e7f5e89cb..82edd5f88a32 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -955,8 +955,6 @@ static struct kobj_type padata_attr_type = {
  * @name: used to identify the instance
  * @pcpumask: cpumask that will be used for padata parallelization
  * @cbcpumask: cpumask that will be used for padata serialization
- *
- * Must be called from a cpus_read_lock() protected region
  */
 static struct padata_instance *padata_alloc(const char *name,
 					    const struct cpumask *pcpumask,
@@ -974,11 +972,13 @@ static struct padata_instance *padata_alloc(const char *name,
 	if (!pinst->wq)
 		goto err_free_inst;
 
+	get_online_cpus();
+
 	if (!alloc_cpumask_var(&pinst->cpumask.pcpu, GFP_KERNEL))
-		goto err_free_wq;
+		goto err_put_cpus;
 	if (!alloc_cpumask_var(&pinst->cpumask.cbcpu, GFP_KERNEL)) {
 		free_cpumask_var(pinst->cpumask.pcpu);
-		goto err_free_wq;
+		goto err_put_cpus;
 	}
 	if (!padata_validate_cpumask(pinst, pcpumask) ||
 	    !padata_validate_cpumask(pinst, cbcpumask))
@@ -1002,12 +1002,16 @@ static struct padata_instance *padata_alloc(const char *name,
 #ifdef CONFIG_HOTPLUG_CPU
 	cpuhp_state_add_instance_nocalls_cpuslocked(hp_online, &pinst->node);
 #endif
+
+	put_online_cpus();
+
 	return pinst;
 
 err_free_masks:
 	free_cpumask_var(pinst->cpumask.pcpu);
 	free_cpumask_var(pinst->cpumask.cbcpu);
-err_free_wq:
+err_put_cpus:
+	put_online_cpus();
 	destroy_workqueue(pinst->wq);
 err_free_inst:
 	kfree(pinst);
@@ -1021,12 +1025,9 @@ static struct padata_instance *padata_alloc(const char *name,
  *                         parallel workers.
  *
  * @name: used to identify the instance
- *
- * Must be called from a cpus_read_lock() protected region
  */
 struct padata_instance *padata_alloc_possible(const char *name)
 {
-	lockdep_assert_cpus_held();
 	return padata_alloc(name, cpu_possible_mask, cpu_possible_mask);
 }
 EXPORT_SYMBOL(padata_alloc_possible);
-- 
2.22.0