2022-03-29 08:35:27

by daihuaigang129

Subject: [PATCH v1] bcache: fix AB-BA deadlock between cache register and cache_set_free

From: daihuaigang <[email protected]>

bcache register add kobject_mutex then bch_register_mutex,
cache_set_free add bch_register_mutex then kobject_mutex.
fix AB-BA deadlock between cache register and cache_set_free.

Signed-off-by: daihuaigang <[email protected]>
---
drivers/md/bcache/super.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index bf3de14..f17953c 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1690,10 +1690,8 @@ static void cache_set_free(struct closure *cl)
if (ca) {
ca->set = NULL;
c->cache = NULL;
- kobject_put(&ca->kobj);
}

-
if (c->moving_gc_wq)
destroy_workqueue(c->moving_gc_wq);
bioset_exit(&c->bio_split);
@@ -1704,6 +1702,8 @@ static void cache_set_free(struct closure *cl)

list_del(&c->list);
mutex_unlock(&bch_register_lock);
+ if (ca)
+ kobject_put(&ca->kobj);

pr_info("Cache set %pU unregistered\n", c->set_uuid);
wake_up(&unregister_wait);
--
1.8.3.1

2022-04-07 20:41:24

by Coly Li

Subject: Re: [PATCH v1] bcache: fix AB-BA deadlock between cache register and cache_set_free

On 3/29/22 11:17 AM, [email protected] wrote:
> From: daihuaigang <[email protected]>
>
> bcache register add kobject_mutex then bch_register_mutex,
> cache_set_free add bch_register_mutex then kobject_mutex.
> fix AB-BA deadlock between cache register and cache_set_free.

Can you explain a bit more about,

- For "bcache register add kobject_mutex", which function referred by
"bcache register add", and where is the kobject_mutex.

- Where is bch_regsiter_mutex.

It is not clear for me to understand how hte AB-BA deadlock generated yet.

Thanks.


Coly Li


>
> Signed-off-by: daihuaigang <[email protected]>
> ---
> drivers/md/bcache/super.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index bf3de14..f17953c 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1690,10 +1690,8 @@ static void cache_set_free(struct closure *cl)
> if (ca) {
> ca->set = NULL;
> c->cache = NULL;
> - kobject_put(&ca->kobj);
> }
>
> -
> if (c->moving_gc_wq)
> destroy_workqueue(c->moving_gc_wq);
> bioset_exit(&c->bio_split);
> @@ -1704,6 +1702,8 @@ static void cache_set_free(struct closure *cl)
>
> list_del(&c->list);
> mutex_unlock(&bch_register_lock);
> + if (ca)
> + kobject_put(&ca->kobj);
>
> pr_info("Cache set %pU unregistered\n", c->set_uuid);
> wake_up(&unregister_wait);