Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752860AbcDFRjL (ORCPT ); Wed, 6 Apr 2016 13:39:11 -0400 Received: from mail-pf0-f170.google.com ([209.85.192.170]:35304 "EHLO mail-pf0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914AbcDFRjI (ORCPT ); Wed, 6 Apr 2016 13:39:08 -0400 Date: Wed, 6 Apr 2016 10:38:48 -0700 From: Dmitry Torokhov To: Aniroop Mathur Cc: Henrik Rydberg , Aniroop Mathur , "linux-input@vger.kernel.org" , lkml Subject: Re: [PATCH] Input: Do not add SYN_REPORT in between a single packet data Message-ID: <20160406173848.GC38452@dtor-ws> References: <1457372672-884-1-git-send-email-a.mathur@samsung.com> <56E17A73.8090901@bitmath.org> <20160401215128.GA5216@dtor-ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5422 Lines: 129 On Wed, Apr 06, 2016 at 08:26:39PM +0530, Aniroop Mathur wrote: > On Sat, Apr 2, 2016 at 10:31 PM, Aniroop Mathur > wrote: > > Hello Mr. Torokhov, > > > > First of all, Thank you for your reply. > > > > On Sat, Apr 2, 2016 at 3:21 AM, Dmitry Torokhov > > wrote: > >> On Fri, Mar 11, 2016 at 12:26:57AM +0530, Aniroop Mathur wrote: > >>> Hi Henrik, > >>> > >>> On Thu, Mar 10, 2016 at 7:15 PM, Henrik Rydberg wrote: > >>> > Hi Dmitry, > >>> > > >>> >>> diff --git a/drivers/input/input.c b/drivers/input/input.c > >>> >>> index 8806059..262ef77 100644 > >>> >>> --- a/drivers/input/input.c > >>> >>> +++ b/drivers/input/input.c > >>> >>> @@ -401,8 +401,7 @@ static void input_handle_event(struct input_dev *dev, > >>> >>> if (dev->num_vals >= 2) > >>> >>> input_pass_values(dev, dev->vals, dev->num_vals); > >>> >>> dev->num_vals = 0; > >>> >>> - } else if (dev->num_vals >= dev->max_vals - 2) { > >>> >>> - dev->vals[dev->num_vals++] = input_value_sync; > >>> >>> + } else if (dev->num_vals >= dev->max_vals - 1) { > >>> >>> input_pass_values(dev, dev->vals, dev->num_vals); > >>> >>> dev->num_vals = 0; > >>> >>> } > >>> >> > >>> >> This makes sense to me. Henrik? > >>> > > >>> > I went through the commits that made these changes, and I cannot see any strong > >>> > reason to keep it. However, this code path only triggers if no SYN events are > >>> > seen, as in a driver that fails to emit them and consequently fills up the > >>> > buffer. In other words, this change would only affect a device that is already, > >>> > to some degree, broken. > >>> > > >>> > So, the question to Aniroop is: do you see this problem in practise, and in that > >>> > case, for what driver? > >>> > > >>> > >>> Nope. So far I have not dealt with any such driver. > >>> I made this change because it is breaking protocol of SYN_REPORT event code. > >>> > >>> Further from the code, I could deduce that max_vals is just an estimation of > >>> packet_size and it does not guarantee that packet_size is same as max_vals. > >>> So real packet_size can be more than max_vals value and hence we could not > >>> insert SYN_REPORT until packet ends really. > >>> Further, if we consider that there exists a driver or will exist in future > >>> which sets capability of x event code according to which max_value comes out to > >>> y and the real packet size is z i.e. driver wants to send same event codes > >>> again in the same packet, so input event reader would be expecting SYN_REPORT > >>> after z events but due to current code SYN_REPORT will get inserted > >>> automatically after y events, which is a wrong behaviour. > >> > >> Well, I think I agree with Aniroop that even if driver is to a degree > >> broken we should not be inserting random SYN_REPORT events into the > >> stream. I wonder if we should not add WARN_ONCE() there to highlight > >> potential problems with the way we estimate the number of events. > >> > >> However I think there is an issue with the patch. If we happen to pass > >> values just before the final SYN_REPORT sent by the driver then we reset > >> dev->num_vals to 0 and will essentially suppress the final SYN_REPORT > >> event, which is not good either. > >> > > > > Yes, right! > > > > I think it can be fixed by sending the rest of events but not the last event > > in case number of events becomes greater than max_vals. The last event will be > > saved to be sent in next set of events. This way immediate SYN_REPORT will not > > be suppressed and duplicate SYN_REPORT event will not be sent as well. > > > > Change: > > @@ -401,8 +401,7 @@ static void input_handle_event(struct input_dev *dev, > > if (dev->num_vals >= 2) > > input_pass_values(dev, dev->vals, dev->num_vals); > > dev->num_vals = 0; > > - } else if (dev->num_vals >= dev->max_vals - 2) { > > - dev->vals[dev->num_vals++] = input_value_sync; > > - input_pass_values(dev, dev->vals, dev->num_vals); > > - dev->num_vals = 0; > > + } else if (dev->num_vals == dev->max_vals) { > > + input_pass_values(dev, dev->vals, dev->num_vals - 1); > > + dev->num_vals = 0; > > + dev->vals[dev->num_vals++] = dev->vals[dev->max_vals - 1]; > > } > > > > So, does the above patch looks good now? > > No, consider what will happen if you need to switch slot when your queue is at dev->max_vals - 1. With your patch you will end up with out of bounds write. > > > Hello Mr. Torokhov, > > Could you please update about this? > It would be appreciating if you could help out to conclude it quickly. Thanks! I am not sure what the urgency is. It is more of a theoretical problem ans so far the proposed solutions were actually introducing more problems than they were solving. I am sorry, bit this particular topic is not a priority for me. > > > > And may be about WARN_ONCE, do you mean to add something like below in above > > code? > > WARN_ONCE(1, "Packet did not complete yet but generally expected to be > > completed before generation of %d events.\n", dev->max_vals); > > > > > > Thanks, > > Aniroop Mathur > > > >> Thanks. > >> > >> -- > >> Dmitry Thanks. -- Dmitry