[PATCH v2] drivers: hv: vmbus: Add missing check for dma_set_mask in vmbus_device_register()

[Haoxiang Li]

child_device_obj->device cannot perform DMA properly if dma_set_mask()
returns non-zero. Add check for dma_set_mask() and return the error if it
fails. To do the right cleanup, call dma_set_mask() after device_register()
so that we can use existent error path of vmbus_device_register().

Fixes: 3a5469582c24 ("Drivers: hv: vmbus: Fix initialization of device object 
in vmbus_device_register()")
Signed-off-by: Haoxiang Li <mak...@iscas.ac.cn>
---
Changes in v2:
Thanks for your comments. They help a lot. It is not sufficient to do the
cleanup just with kfree(). The memory allocated by dev_set_name()
should also be freed, which is done by put_device() (finally in
kobject_cleanup() [1]). I think performing a complete cleanup within
vmbus_device_register() would be verbose and detrimental to code
maintenance. I suggest calling dma_set_mask() after device_register(),
so that proper error handling can be achieved using the existent error path
of vmbus_device_register(), i.e., err_dev_unregister [2]. Moreover,
I found a similar usage in dmapool_checks() [3], which calls
dma_set_mask_and_coherent() after device_register(). I believe the
modification is workable.

Reference link:
[1]https://github.com/torvalds/linux/blob/master/lib/kobject.c#L695
[2]https://github.com/torvalds/linux/blob/master/drivers/hv/vmbus_drv.c#L1933
[3]https://github.com/torvalds/linux/blob/master/mm/dmapool_test.c#L105
---
 drivers/hv/vmbus_drv.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 12a707ab73f8..f3999d8afd77 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1897,7 +1897,6 @@ int vmbus_device_register(struct hv_device 
*child_device_obj)
 
        child_device_obj->device.dma_parms = &child_device_obj->dma_parms;
        child_device_obj->device.dma_mask = &child_device_obj->dma_mask;
-       dma_set_mask(&child_device_obj->device, DMA_BIT_MASK(64));
 
        /*
         * Register with the LDM. This will kick off the driver/device
@@ -1910,6 +1909,12 @@ int vmbus_device_register(struct hv_device 
*child_device_obj)
                return ret;
        }
 
+       ret = dma_set_mask(&child_device_obj->device, DMA_BIT_MASK(64));
+       if (ret) {
+               pr_err("64-bit DMA enable failed!\n");
+               goto err_dev_unregister;
+       }
+
        child_device_obj->channels_kset = kset_create_and_add("channels",
                                                              NULL, kobj);
        if (!child_device_obj->channels_kset) {
-- 
2.25.1