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

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Date:   Fri, 20 Mar 2020 09:26:50 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     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 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.

							Thanx, Paul