Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753149AbcDFTJW (ORCPT ); Wed, 6 Apr 2016 15:09:22 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:35218 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751900AbcDFTJT (ORCPT ); Wed, 6 Apr 2016 15:09:19 -0400 MIME-Version: 1.0 In-Reply-To: <20160406173848.GC38452@dtor-ws> References: <1457372672-884-1-git-send-email-a.mathur@samsung.com> <56E17A73.8090901@bitmath.org> <20160401215128.GA5216@dtor-ws> <20160406173848.GC38452@dtor-ws> Date: Thu, 7 Apr 2016 00:39:17 +0530 Message-ID: Subject: Re: [PATCH] Input: Do not add SYN_REPORT in between a single packet data From: Aniroop Mathur To: Dmitry Torokhov Cc: Henrik Rydberg , Aniroop Mathur , "linux-input@vger.kernel.org" , lkml Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6833 Lines: 161 On Wed, Apr 6, 2016 at 11:08 PM, Dmitry Torokhov wrote: > 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. > Sorry, I know very less about MT protocol, so could not catch this. I have worked only on normal input device drivers. input_abs_set_val(dev, ABS_MT_SLOT, mt->slot); --> I guess I missed this? :( I have modified condition to handle it, so does it look fine now? diff --git a/drivers/input/input.c b/drivers/input/input.c index 8806059..799941c 100644 --- a/drivers/input/input.c +++ b/drivers/input/input.c @@ -401,12 +401,11 @@ 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); + } else if (dev->num_vals >= dev->max_vals - 1) { + input_pass_values(dev, dev->vals, dev->num_vals - 1); dev->num_vals = 0; + dev->vals[dev->num_vals++] = dev->vals[dev->num_vals - 1]; } - } >> >> >> 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. > There is no hurry at all. :-) As you know request is made a long time ago, so I am only very curious to complete it. >> >> >> > 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