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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Pavel Skripkin <paskripkin@gmail.com>
Cc: Larry Finger <Larry.Finger@lwfinger.net>,
	Phillip Potter <phil@philpotter.co.uk>,
	linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org,
	David Laight <david.Laight@aculab.com>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	"Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Subject: Re: [PATCH v7 19/19] staging: r8188eu: remove shared buffer for usb requests
Date: Fri, 17 Sep 2021 17:18:13 +0200	[thread overview]
Message-ID: <YUSxtQ7D0w6QkB/N@kroah.com> (raw)
In-Reply-To: <ef2a89f5-f68c-e7e2-9338-78e70dc41701@gmail.com>

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@gmail.com>
> > > 
> > > 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

  parent reply	other threads:[~2021-09-17 15:20 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-17  7:18 [PATCH v7 00/19] staging: r8188eu: shorten and simplify calls chains Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 01/19] staging: r8188eu: remove usb_{read,write}_mem() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 02/19] staging: r8188eu: remove the helpers of rtw_read8() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 03/19] staging: r8188eu: remove the helpers of rtw_read16() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 04/19] staging: r8188eu: remove the helpers of rtw_read32() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 05/19] staging: r8188eu: remove the helpers of usb_write8() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 06/19] staging: r8188eu: remove the helpers of usb_write16() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 07/19] staging: r8188eu: remove the helpers of usb_write32() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 08/19] staging: r8188eu: remove the helpers of usb_writeN() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 09/19] staging: r8188eu: remove the helpers of usb_read_port() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 10/19] staging: r8188eu: remove the helpers of usb_write_port() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 11/19] staging: r8188eu: remove the helpers of usb_read_port_cancel() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 12/19] staging: r8188eu: remove the helpers of usb_write_port_cancel() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 13/19] staging: r8188eu: remove core/rtw_io.c Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 14/19] staging: r8188eu: remove struct _io_ops Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 15/19] staging: r8188eu: clean up usbctrl_vendorreq() Fabio M. De Francesco
2021-09-17 14:44   ` Greg Kroah-Hartman
2021-09-18 11:13     ` Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 16/19] staging: r8188eu: clean up rtw_read*() and rtw_write*() Fabio M. De Francesco
2021-09-17 14:44   ` Greg Kroah-Hartman
2021-09-17 14:45   ` Greg Kroah-Hartman
2021-09-18 11:41     ` Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 17/19] staging: r8188eu: shorten calls chain of rtw_read{8,16,32}() Fabio M. De Francesco
2021-09-17 14:50   ` Greg Kroah-Hartman
2021-09-17 15:01     ` David Laight
2021-09-17 15:17       ` 'Greg Kroah-Hartman'
2021-09-18 12:19     ` Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 18/19] staging: r8188eu: shorten calls chain of rtw_write{8,16,32,N}() Fabio M. De Francesco
2021-09-17  7:18 ` [PATCH v7 19/19] staging: r8188eu: remove shared buffer for usb requests Fabio M. De Francesco
2021-09-17 14:55   ` Greg Kroah-Hartman
2021-09-17 15:03     ` Pavel Skripkin
2021-09-17 15:06       ` Pavel Skripkin
2021-09-17 15:18       ` Greg Kroah-Hartman [this message]
2021-09-17 15:23         ` Pavel Skripkin
2021-09-17 11:07 ` [PATCH v7 00/19] staging: r8188eu: shorten and simplify calls chains Dan Carpenter

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