Re: [PATCH] rbd: prevent busy loop when requesting exclusive lock

[Dongsheng Yang <dongsheng.yang@easystack.cn>]

Hi Ilya

在 2023/8/2 星期三 上午 6:22, Ilya Dryomov 写道:
> Due to rbd_try_acquire_lock() effectively swallowing all but
> EBLOCKLISTED error from rbd_try_lock() ("request lock anyway") and
> rbd_request_lock() returning ETIMEDOUT error not only for an actual
> notify timeout but also when the lock owner doesn't respond, a busy
> loop inside of rbd_acquire_lock() between rbd_try_acquire_lock() and
> rbd_request_lock() is possible.
> 
> Requesting the lock on EBUSY error (returned by get_lock_owner_info()
> if an incompatible lock or invalid lock owner is detected) makes very
> little sense.  The same goes for ETIMEDOUT error (might pop up pretty
> much anywhere if osd_request_timeout option is set) and many others.
> 
> Just fail I/O requests on rbd_dev->acquiring_list immediately on any
> error from rbd_try_lock().
> 
> Cc: stable@vger.kernel.org # 588159009d5b: rbd: retrieve and check lock owner twice before blocklisting
> Cc: stable@vger.kernel.org
> Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
> ---
>   drivers/block/rbd.c | 28 +++++++++++++++-------------
>   1 file changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 24afcc93ac01..2328cc05be36 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -3675,7 +3675,7 @@ static int rbd_lock(struct rbd_device *rbd_dev)
>   	ret = ceph_cls_lock(osdc, &rbd_dev->header_oid, &rbd_dev->header_oloc,
>   			    RBD_LOCK_NAME, CEPH_CLS_LOCK_EXCLUSIVE, cookie,
>   			    RBD_LOCK_TAG, "", 0);
> -	if (ret)
> +	if (ret && ret != -EEXIST)
>   		return ret;
>   
>   	__rbd_lock(rbd_dev, cookie);

If we got -EEXIST here, we will call __rbd_lock() and return 0. -EEXIST 
means lock is held by myself, is that necessary to call __rbd_lock()?