linux-kernel - Re: linux-next build error (8)

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Date:   Fri, 20 Mar 2020 10:04:40 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+792dec47d693ccdc05a0@...kaller.appspotmail.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: linux-next build error (8)

On Fri, Mar 20, 2020 at 09:34:13AM -0700, Randy Dunlap wrote:
> On 3/20/20 9:26 AM, Paul E. McKenney wrote:
> > On Fri, Mar 20, 2020 at 04:38:54PM +0100, Dmitry Vyukov wrote:
> >> On Thu, Mar 19, 2020 at 4:04 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> >>>
> >>> On Thu, Mar 19, 2020 at 08:13:35AM +0100, Dmitry Vyukov wrote:
> >>>> On Wed, Mar 18, 2020 at 10:41 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> >>>>>
> >>>>> On Wed, Mar 18, 2020 at 09:54:07PM +0100, Dmitry Vyukov wrote:
> >>>>>> On Wed, Mar 18, 2020 at 5:57 PM syzbot
> >>>>>> <syzbot+792dec47d693ccdc05a0@...kaller.appspotmail.com> wrote:
> >>>>>>>
> >>>>>>> Hello,
> >>>>>>>
> >>>>>>> syzbot found the following crash on:
> >>>>>>>
> >>>>>>> HEAD commit:    47780d78 Add linux-next specific files for 20200318
> >>>>>>> git tree:       linux-next
> >>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=14228745e00000
> >>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=b68b7b89ad96c62a
> >>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=792dec47d693ccdc05a0
> >>>>>>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> >>>>>>>
> >>>>>>> Unfortunately, I don't have any reproducer for this crash yet.
> >>>>>>>
> >>>>>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> >>>>>>> Reported-by: syzbot+792dec47d693ccdc05a0@...kaller.appspotmail.com
> >>>>>>>
> >>>>>>> kernel/rcu/tasks.h:1070:37: error: 'rcu_tasks_rude' undeclared (first use in this function); did you mean 'rcu_tasks_qs'?
> >>>>>>
> >>>>>> +rcu maintainers
> >>>>>
> >>>>> The kbuild test robot beat you to it, and apologies for the hassle.
> >>>>> Fixed in -rcu on current "dev" branch.
> >>>>
> >>>> If the kernel dev process would only have a way to avoid dups from all
> >>>> test systems...
> >>>
> >>> I do significant testing before pushing to -next, but triggering this
> >>> one requires a combination of Kconfig options that are incompatible
> >>> with rcutorture.  :-/
> >>>
> >>> I suppose one strategy would be to give kbuild test robot some time before
> >>> passing to -next, but they seem to sometimes get too far behind for me to
> >>> be willing to wait that long.  So my current approach is to push my "dev"
> >>> branch, run moderate rcutorture testing (three hours per scenario other
> >>> than TREE10, which gets only one hour), and if that passes, push to -next.
> >>>
> >>> I suppose that I could push to -next only commits that are at least three
> >>> days old or some such.  But I get in trouble pushing to -next too slowly
> >>> as often as I get in trouble pushing too quickly, so I suspect that my
> >>> current approach is in roughly the right place.
> >>>
> >>>> Now we need to spend time and deal with it. What has fixed it?
> >>>
> >>> It is fixed by commit c6ef38e4d595 ("rcu-tasks: Add RCU tasks to
> >>> rcutorture writer stall output") and some of its predecessors.
> >>>
> >>> Perhaps more useful to you, this commit is included in next-20200319
> >>> from the -next tree.  ;-)
> >>
> >> Let's tell syzbot about the fix:
> >>
> >> #syz fix: rcu-tasks: Add RCU tasks to rcutorture writer stall output
> >>
> >> I think what you are doing is the best possible option in the current situation.
> >> I don't think requiring all human maintainers to do more manual
> >> repetitive work, which is not well defined and even without a way to
> >> really require something from them is scalable nor reliable nor the
> >> right approach.
> > 
> > Thank you, and I do greatly appreciate the automation!
> > 
> >> We would consume something like LKGR [1] if it existed for the kernel.
> >> But it would require tighter integration of testing systems with
> >> kernel dev processes, or of course throwing more manual labor at it to
> >> track all uncoordinated testing systems and publishing LKGR tags.
> >>
> >> [1] https://chromium.googlesource.com/chromiumos/docs/+/master/glossary.md
> > 
> > At my end, it is pretty quick and easy to detect duplicate notifications
> > of the same bug, so the current situation isn't causing me undue distress.
> 
> Yeah, I saw the same build error and did-not-report it since it was
> already reported.  :)

Much appreciated!  ;-)

							Thanx, Paul