[PATCH v2 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.jor...@oracle.com>
Acked-by: Steffen Klassert <steffen.klass...@secunet.com>
Cc: Herbert Xu <herb...@gondor.apana.org.au>
Cc: Lai Jiangshan <jiangshan...@gmail.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Tejun Heo <t...@kernel.org>
Cc: linux-crypto@vger.kernel.org
Cc: linux-ker...@vger.kernel.org
---
 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 863053a1e379..29d44edd6733 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -907,8 +907,6 @@ 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,
@@ -926,11 +924,13 @@ 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))
@@ -956,12 +956,16 @@ static struct padata_instance *padata_alloc(const char 
*name,
        cpuhp_state_add_instance_nocalls_cpuslocked(CPUHP_PADATA_DEAD,
                                                    &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);
@@ -975,12 +979,9 @@ 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);
-- 
2.23.0