[PATCH V5 1/3] percpu_ref: add percpu_ref_is_initialized for MD

[PATCH V5 1/3] percpu_ref: add percpu_ref_is_initialized for MD

[Ming Lei]

MD code uses perpcu-refcount internal to check if this percpu-refcount
variable is initialized, this way is a hack.

Add percpu_ref_is_initialized for MD so that the hack can be avoided.

Acked-by: Song Liu <song@kernel.org>
Suggested-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Veronika Kabatova <vkabatov@redhat.com>
Cc: Song Liu <song@kernel.org>
Cc: linux-raid@vger.kernel.org
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/md/md.c                 | 2 +-
 include/linux/percpu-refcount.h | 1 +
 lib/percpu-refcount.c           | 6 ++++++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index de8419b7ae98..241ff618d84e 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5631,7 +5631,7 @@ static void no_op(struct percpu_ref *r) {}
 
 int mddev_init_writes_pending(struct mddev *mddev)
 {
-	if (mddev->writes_pending.percpu_count_ptr)
+	if (percpu_ref_is_initialized(&mddev->writes_pending))
 		return 0;
 	if (percpu_ref_init(&mddev->writes_pending, no_op,
 			    PERCPU_REF_ALLOW_REINIT, GFP_KERNEL) < 0)
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 87d8a38bdea1..2dfdf870f2d0 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -109,6 +109,7 @@ struct percpu_ref {
 int __must_check percpu_ref_init(struct percpu_ref *ref,
 				 percpu_ref_func_t *release, unsigned int flags,
 				 gfp_t gfp);
+bool percpu_ref_is_initialized(struct percpu_ref *ref);
 void percpu_ref_exit(struct percpu_ref *ref);
 void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
 				 percpu_ref_func_t *confirm_switch);
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 0ba686b8fe57..db2ec682e0f7 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -93,6 +93,12 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
 }
 EXPORT_SYMBOL_GPL(percpu_ref_init);
 
+bool percpu_ref_is_initialized(struct percpu_ref *ref)
+{
+	return percpu_count_ptr(ref) != NULL;
+}
+EXPORT_SYMBOL_GPL(percpu_ref_is_initialized);
+
 /**
  * percpu_ref_exit - undo percpu_ref_init()
  * @ref: percpu_ref to exit
-- 
2.25.2

Re: [PATCH V5 1/3] percpu_ref: add percpu_ref_is_initialized for MD

[Christoph Hellwig]

On Sun, Sep 27, 2020 at 02:26:52PM +0800, Ming Lei wrote:
> MD code uses perpcu-refcount internal to check if this percpu-refcount
> variable is initialized, this way is a hack.
> 
> Add percpu_ref_is_initialized for MD so that the hack can be avoided.
> 
> Acked-by: Song Liu <song@kernel.org>
> Suggested-by: Jens Axboe <axboe@kernel.dk>
> Tested-by: Veronika Kabatova <vkabatov@redhat.com>
> Cc: Song Liu <song@kernel.org>
> Cc: linux-raid@vger.kernel.org
> Cc: Sagi Grimberg <sagi@grimberg.me>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Bart Van Assche <bvanassche@acm.org>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/md/md.c                 | 2 +-
>  include/linux/percpu-refcount.h | 1 +
>  lib/percpu-refcount.c           | 6 ++++++
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index de8419b7ae98..241ff618d84e 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -5631,7 +5631,7 @@ static void no_op(struct percpu_ref *r) {}
>  
>  int mddev_init_writes_pending(struct mddev *mddev)
>  {
> -	if (mddev->writes_pending.percpu_count_ptr)
> +	if (percpu_ref_is_initialized(&mddev->writes_pending))
>  		return 0;

I'd much rather use a flag in the containing mddev structure then
exposing this new "API".  That mddev code is pretty gross to be honest,
we should just initialize the percpu_ref once instea of such a hack.