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    Subject[patch V3 07/32] padata: Avoid nested calls to cpus_read_lock() in pcrypt_init_padata()
    From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

    pcrypt_init_padata()
    cpus_read_lock()
    padata_alloc_possible()
    padata_alloc()
    cpus_read_lock()

    The nested call to cpus_read_lock() 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 cpus_read_lock() protected region as well.

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

    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Steffen Klassert <steffen.klassert@secunet.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: linux-crypto@vger.kernel.org

    ---
    kernel/padata.c | 11 ++++++-----
    1 file changed, 6 insertions(+), 5 deletions(-)

    --- a/kernel/padata.c
    +++ b/kernel/padata.c
    @@ -940,6 +940,8 @@ 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 cpus_read_lock() protected region
    */
    static struct padata_instance *padata_alloc(struct workqueue_struct *wq,
    const struct cpumask *pcpumask,
    @@ -952,7 +954,6 @@ static struct padata_instance *padata_al
    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)) {
    @@ -976,14 +977,12 @@ static struct padata_instance *padata_al

    pinst->flags = 0;

    - put_online_cpus();
    -
    BLOCKING_INIT_NOTIFIER_HEAD(&pinst->cpumask_change_notifier);
    kobject_init(&pinst->kobj, &padata_attr_type);
    mutex_init(&pinst->lock);

    #ifdef CONFIG_HOTPLUG_CPU
    - cpuhp_state_add_instance_nocalls(hp_online, &pinst->node);
    + cpuhp_state_add_instance_nocalls_cpuslocked(hp_online, &pinst->node);
    #endif
    return pinst;

    @@ -992,7 +991,6 @@ static struct padata_instance *padata_al
    free_cpumask_var(pinst->cpumask.cbcpu);
    err_free_inst:
    kfree(pinst);
    - put_online_cpus();
    err:
    return NULL;
    }
    @@ -1003,9 +1001,12 @@ static struct padata_instance *padata_al
    * parallel workers.
    *
    * @wq: workqueue to use for the allocated padata instance
    + *
    + * Must be called from a cpus_read_lock() protected region
    */
    struct padata_instance *padata_alloc_possible(struct workqueue_struct *wq)
    {
    + lockdep_assert_cpus_held();
    return padata_alloc(wq, cpu_possible_mask, cpu_possible_mask);
    }
    EXPORT_SYMBOL(padata_alloc_possible);

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