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 :) thanks, greg k-h
