Re: [PATCH v7 19/19] staging: r8188eu: remove shared buffer for usb requests

[Pavel Skripkin]

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