From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ABBE429CA for ; Fri, 17 Sep 2021 15:18:15 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id CC5EC61164; Fri, 17 Sep 2021 15:18:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631891895; bh=96NVuakQJdmaO277CeGDiyCBNXhMgA/638vNRLesnyc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gYxvoiO1I1AqWfBxf49rIRQgHssvElBbASOYmcN03uAx8XkjMi30rkGKyC6p9X3aE l1671X4Q95CkCh9/kN89XUfd3HU80h1TP0EsOLmAkm+GVVKx3yGNbuQZNM5R1GIJgY jI61iXwzKsAQyc3QcFU7qeiDnWgGtNWrFJsZFmqY= Date: Fri, 17 Sep 2021 17:18:13 +0200 From: Greg Kroah-Hartman To: Pavel Skripkin Cc: Larry Finger , Phillip Potter , linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, David Laight , Dan Carpenter , "Fabio M. De Francesco" Subject: Re: [PATCH v7 19/19] staging: r8188eu: remove shared buffer for usb requests Message-ID: References: <20210917071837.10926-1-fmdefrancesco@gmail.com> <20210917071837.10926-20-fmdefrancesco@gmail.com> Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 > > > > > > 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