Re: [PATCH v2 10/24] uas: zap_pending: data urbs should have completed at this time

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 09/14/2014 12:29 PM, James Bottomley wrote:
> On Sun, 2014-09-14 at 11:26 +0200, Hans de Goede wrote:
>> Hi,
>>
>> On 09/13/2014 09:31 PM, Sergei Shtylyov wrote:
>>> Hello.
>>>
>>> On 9/13/2014 1:26 PM, Hans de Goede wrote:
>>>
>>>> The data urbs are all killed before calling zap_pending, and their completion
>>>> handler should have cleared their inflight flag.
>>>
>>>> Do not 0 the data inflight flags, and add a check for try_complete succeeding,
>>>> as it should always succeed when called from zap_pending.
>>>
>>>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>>>> ---
>>>>   drivers/usb/storage/uas.c | 10 +++++-----
>>>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
>>>> index 08edb6b..85bbc1d 100644
>>>> --- a/drivers/usb/storage/uas.c
>>>> +++ b/drivers/usb/storage/uas.c
>>>> @@ -145,6 +145,7 @@ static void uas_zap_pending(struct uas_dev_info *devinfo, int result)
>>>>       struct uas_cmd_info *cmdinfo;
>>>>       struct uas_cmd_info *temp;
>>>>       unsigned long flags;
>>>> +    int err;
>>>
>>>    Er, I don't see why this variable is necessary.
>>>
>>> [...]
>>>> @@ -152,12 +153,11 @@ static void uas_zap_pending(struct uas_dev_info *devinfo, int result)
>>>>           struct scsi_cmnd *cmnd = container_of(scp, struct scsi_cmnd,
>>>>                                 SCp);
>>>>           uas_log_cmd_state(cmnd, __func__);
>>>> -        /* all urbs are killed, clear inflight bits */
>>>> -        cmdinfo->state &= ~(COMMAND_INFLIGHT |
>>>> -                    DATA_IN_URB_INFLIGHT |
>>>> -                    DATA_OUT_URB_INFLIGHT);
>>>> +        /* Sense urbs were killed, clear COMMAND_INFLIGHT manually */
>>>> +        cmdinfo->state &= ~COMMAND_INFLIGHT;
>>>>           cmnd->result = result << 16;
>>>> -        uas_try_complete(cmnd, __func__);
>>>> +        err = uas_try_complete(cmnd, __func__);
>>>> +        WARN_ON(err != 0);
>>>
>>>    Why not:
>>>
>>>         WARN_ON(uas_try_complete(cmnd, __func__));
>>>
>>
>> This was discussed already during v1 of this patch-set, WARN_ON may
>> not have a side-effect, as it may be defined as an empty macro.
> 
> Must have missed the discussion, but whoever said that loses all their
> review points.  We're very careful to make sure that even in the case
> where WARN_ON and BUG_ON (and indeed any macros) are compiled out, the
> side effects are still accounted for.  This is the canonical definition
> of WARN_ON in the compiled out case:
> 
> #define WARN_ON(condition) ({						\
> 	int __ret_warn_on = !!(condition);				\
> 	unlikely(__ret_warn_on);					\
> })
> 
> So the compiler will eliminate the statement only if there are no side
> effects.

Ah that is good to know. Still I would like to stick with the new version
(which adds the err), as I believe that that code is more readable.

AFAIK in general the kernel coding style is to favor:

err = func();
if (err)

over:

if (func())

And this is sorta the same.

Regards,

Hans