linux-kernel - Re: [Ksummit-discuss] bug-introducing patches

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Date:   Mon, 14 May 2018 17:25:48 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        "ksummit-discuss@...ts.linuxfoundation.org" 
        <ksummit-discuss@...ts.linuxfoundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "w@....eu" <w@....eu>
Subject: Re: [Ksummit-discuss] bug-introducing patches

On Mon, May 14, 2018 at 10:48:03AM +0200, Boris Brezillon wrote:
>+Fengguang
>
>On Mon, 14 May 2018 10:40:10 +0200
>Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
>> Hi Boris,
>>
>> On Mon, May 14, 2018 at 10:34 AM, Boris Brezillon
>> <boris.brezillon@...tlin.com> wrote:
>> > On Mon, 14 May 2018 10:29:04 +0200
>> > Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> >> On Mon, May 14, 2018 at 10:12 AM, Boris Brezillon
>> >> <boris.brezillon@...tlin.com> wrote:
>> >> > On Mon, 14 May 2018 10:00:30 +0200
>> >> > Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> >> >> On Tue, May 1, 2018 at 10:00 PM, Sasha Levin
>> >> >> <Alexander.Levin@...rosoft.com> wrote:
>> >> >> > On Tue, May 01, 2018 at 03:44:50PM -0400, Theodore Y. Ts'o wrote:
>> >> >> >>On Tue, May 01, 2018 at 04:38:21PM +0000, Sasha Levin wrote:
>> >> >> > What's worse is that that commit is tagged for stable, which means
>> >> >> > that (given Greg's schedule) it may find it's way to -stable users
>> >> >> > even before some -next users/bots had a chance to test it out.
>> >> >>
>> >> >> I just noticed a case where a commit was picked up for stable, while a
>> >> >> bot had flagged it as a build regression 18 hours earlier (with a CC to
>> >> >> lkml).
>> >> >
>> >> > Also, this patch has been on a tree that I know is tested by Fengguang's
>> >> > robots for more than a week (and in linux-next for 2 days, which, I
>> >> > agree, is probably not enough), and still, I only received the bug
>> >> > report when the patch reached mainline. Are there tests that are only
>> >> > run on Linus' tree?
>> >>
>> >> Have your received a success report from Fengguang's bot, listing all
>> >> configs tested (the broken one should be included; it is included in the
>> >> configs tested on my branches)?
>> >
>> > Yes I did (see below).
>> >
>> > -->8--
>> > From: kbuild test robot <lkp@...el.com>
>> > To: Boris Brezillon <boris.brezillon@...tlin.com>
>> > Subject: [bbrezillon-0day:mtd/fixes] BUILD SUCCESS  fc3a9e15b492eef707afd56b7478001fdecfe53f
>> > Date: Mon, 07 May 2018 20:05:52 +0800
>> > User-Agent: Heirloom mailx 12.5 6/20/10
>> >
>> > tree/branch: https://github.com/bbrezillon/linux-0day  mtd/fixes
>> > branch HEAD: fc3a9e15b492eef707afd56b7478001fdecfe53f  mtd: rawnand: Make sure we wait tWB before polling the STATUS reg
>> >
>> > elapsed time: 49m
>> >
>> > configs tested: 142
>>
>> But the failed config (m68k/allmodconfig) is not listed?
>
>Yes, that's my point. It seems that some configs are only rarely
>(never?) tested on my linux-0day tree (probably because they take longer
>to build), and I should only take kbuild robot results as an indication
>not a guarantee.

Yeah sorry, there is no 100% guarantee. There are 2 main aspects to
this problem.

- Response time vs coverage. Most build errors can be caught within 1
  day. The build success notification email is typically sent within
  half day (a reasonable feedback time). At this time, it can only be
  a rough indication not a guarantee. After sending the 0day build
  success notification, the build tests will actually continue for
  about 1 week to increase test coverage. 

- Merge-test-bisect based workflow. If one branch is hard to merge
  with others, especially if it's based on old kernel, it'll receive
  much less test coverage. Branches with known build/boot errors will
  be excluded from further merges, too.

Thanks,
Fengguang