[PATCH] nbd: fix possible sysfs duplicate warning

[PATCH] nbd: fix possible sysfs duplicate warning

[xiubli]

From: Xiubo Li <xiubli@redhat.com>

1. nbd_put takes the mutex and drops nbd->ref to 0. It then does
idr_remove and drops the mutex.

2. nbd_genl_connect takes the mutex. idr_find/idr_for_each fails
to find an existing device, so it does nbd_dev_add.

3. just before the nbd_put could call nbd_dev_remove or not finished
totally, but if nbd_dev_add try to add_disk, we can hit:

debugfs: Directory 'nbd1' with parent 'block' already present!

This patch will make sure all the disk add/remove stuff are done
by holding the nbd_index_mutex lock.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reported-by: Mike Christie <mchristi@redhat.com>
---
 drivers/block/nbd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index ac07e8c94c79..478aa86fc1f2 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -248,8 +248,8 @@ static void nbd_put(struct nbd_device *nbd)
 	if (refcount_dec_and_mutex_lock(&nbd->refs,
 					&nbd_index_mutex)) {
 		idr_remove(&nbd_index_idr, nbd->index);
-		mutex_unlock(&nbd_index_mutex);
 		nbd_dev_remove(nbd);
+		mutex_unlock(&nbd_index_mutex);
 	}
 }
 
-- 
2.21.0

Re: [PATCH] nbd: fix possible sysfs duplicate warning

[Josef Bacik]

On Thu, Sep 19, 2019 at 11:44:27AM +0530, xiubli@redhat.com wrote:
> From: Xiubo Li <xiubli@redhat.com>
> 
> 1. nbd_put takes the mutex and drops nbd->ref to 0. It then does
> idr_remove and drops the mutex.
> 
> 2. nbd_genl_connect takes the mutex. idr_find/idr_for_each fails
> to find an existing device, so it does nbd_dev_add.
> 
> 3. just before the nbd_put could call nbd_dev_remove or not finished
> totally, but if nbd_dev_add try to add_disk, we can hit:
> 
> debugfs: Directory 'nbd1' with parent 'block' already present!
> 
> This patch will make sure all the disk add/remove stuff are done
> by holding the nbd_index_mutex lock.
> 
> Signed-off-by: Xiubo Li <xiubli@redhat.com>
> Reported-by: Mike Christie <mchristi@redhat.com>

Sorry, don't know how I missed this.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

Re: [PATCH] nbd: fix possible sysfs duplicate warning

[Xiubo Li]

On 2019/10/10 21:56, Josef Bacik wrote:
> On Thu, Sep 19, 2019 at 11:44:27AM +0530, xiubli@redhat.com wrote:
>> From: Xiubo Li <xiubli@redhat.com>
>>
>> 1. nbd_put takes the mutex and drops nbd->ref to 0. It then does
>> idr_remove and drops the mutex.
>>
>> 2. nbd_genl_connect takes the mutex. idr_find/idr_for_each fails
>> to find an existing device, so it does nbd_dev_add.
>>
>> 3. just before the nbd_put could call nbd_dev_remove or not finished
>> totally, but if nbd_dev_add try to add_disk, we can hit:
>>
>> debugfs: Directory 'nbd1' with parent 'block' already present!
>>
>> This patch will make sure all the disk add/remove stuff are done
>> by holding the nbd_index_mutex lock.
>>
>> Signed-off-by: Xiubo Li <xiubli@redhat.com>
>> Reported-by: Mike Christie <mchristi@redhat.com>
> Sorry, don't know how I missed this.

Many thanks.

Xiubo

> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
>
> Thanks,
>
> Josef

Re: [PATCH] nbd: fix possible sysfs duplicate warning

[Jens Axboe]

On 9/19/19 12:14 AM, xiubli@redhat.com wrote:
> From: Xiubo Li <xiubli@redhat.com>
> 
> 1. nbd_put takes the mutex and drops nbd->ref to 0. It then does
> idr_remove and drops the mutex.
> 
> 2. nbd_genl_connect takes the mutex. idr_find/idr_for_each fails
> to find an existing device, so it does nbd_dev_add.
> 
> 3. just before the nbd_put could call nbd_dev_remove or not finished
> totally, but if nbd_dev_add try to add_disk, we can hit:
> 
> debugfs: Directory 'nbd1' with parent 'block' already present!
> 
> This patch will make sure all the disk add/remove stuff are done
> by holding the nbd_index_mutex lock.

Applied, thanks.

-- 
Jens Axboe