On Mon, 23 Sep 2019, Greg KH wrote:
> On Mon, Sep 23, 2019 at 03:19:21PM +0900, Austin Kim wrote:
> > Normally when creation of workqueue fails, exception handling takes place
> > after the call to alloc_workqueue() is made.
> >
> > But looking into usb_hub_init() function, 'return 0' statement is executed,
> > when alloc_workqueue() returns valid workqueue pointer.
> > if (hub_wq)
> > return 0;
> >
> > This might make other Linux driver developers get confused
> > because they could deduce that this is exceptional handling routine.
> >
> > So perform minor refactoring by adding NULL pointer dereference check
> > routine right after the call to alloc_workqueue() is made.
> >
> > Signed-off-by: Austin Kim <austindh.kim@xxxxxxxxx>
> > ---
> > drivers/usb/core/hub.c | 7 +++++--
> > 1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index e8ebacc..0ddbfe6 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -5530,9 +5530,12 @@ int usb_hub_init(void)
> > * over to the companion full-speed controller.
> > */
> > hub_wq = alloc_workqueue("usb_hub_wq", WQ_FREEZABLE, 0);
> > - if (hub_wq)
> > - return 0;
> > + if (unlikely(!hub_wq))
>
> Only ever use likely/unlikely if you can measure the difference without
> it. Otherwise the compiler and cpu will almost always do this better
> than you.
>
> So please remove this.
>
> > + goto err_workqueue;
> > +
> > + return 0;
> >
> > +err_workqueue:
> > /* Fall through if kernel_thread failed */
>
> This comment is now incorrect.
>
> But really, there is nothing wrong with the original code here. It
> works properly, and while it is not identical to normal code "style"
> here, there's nothing wrong with it that I can see.
Indeed. In fact, I suspect that this change would make the code less
understandable, because the reader would wonder why anybody would go to
the trouble of jumping over a return statement. After all, this:
if (!test)
jump error;
return 0;
error:
just looks like a strange and inefficient way of writing:
if (test)
return 0;
Anyone reading it would wonder what the original author was thinking.
If you really want to fix up this subroutine, you could change the two
"return -1" statements. They should return an appropriate error code,
not just -1.
Alan Stern
