On 9/17/21 18:18, Greg Kroah-Hartman wrote:
On Fri, Sep 17, 2021 at 06:03:52PM +0300, Pavel Skripkin wrote:
On 9/17/21 17:55, Greg Kroah-Hartman wrote:
> On Fri, Sep 17, 2021 at 09:18:37AM +0200, Fabio M. De Francesco wrote:
> > From: Pavel Skripkin <paskripkin@xxxxxxxxx>
> >
> > This driver used shared buffer for usb requests. It led to using
> > mutexes, i.e no usb requests can be done in parallel.
> >
> > USB requests can be fired in parallel since USB Core allows it. In
> > order to allow them, remove usb_vendor_req_buf from dvobj_priv (since
> > USB I/O is the only user of it) and remove also usb_vendor_req_mutex
> > (since there is nothing to protect).
>
> Ah, you are removing this buffer, nice!
>
> But, just because the USB core allows multiple messages to be sent to a
> device at the same time, does NOT mean that the device itself can handle
> that sort of a thing.
>
> Keeping that lock might be a good idea, until you can prove otherwise.
> You never know, maybe there's never any contention at all for it because
> these accesses are all done in a serial fashion and the lock
> grab/release is instant. But if that is not the case, you might really
> get a device confused here by throwing multiple control messages at it
> in ways that it is not set up to handle at all.
>
> So please do not drop the lock.
>
> More comments below.
>
We have tested this change. I've tested it in qemu with TP-Link TL-WN722N v2
/ v3 [Realtek RTL8188EUS], and Fabio has tested it on his host for like a
whole evening.
I agree, that our testing does not cover all possible cases and I can't say
it was "good stress testing", so, I think, we need some comments from
maintainers.
Ok, then make it a single patch that does nothing but remove the lock so
that we can revert it later when problems show up :)
Sure! Thank you again :)
With regards,
Pavel Skripkin
