netdev - Re: [syzbot] WARNING in trc_read_check

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Date:   Sat, 4 Dec 2021 07:07:59 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+fe9d8c955bd1d0f02dc1@...kaller.appspotmail.com>,
        bigeasy@...utronix.de, jgross@...e.com, jiangshanlai@...il.com,
        joel@...lfernandes.org, josh@...htriplett.org,
        linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com,
        mingo@...nel.org, namit@...are.com, netdev@...r.kernel.org,
        peterz@...radead.org, rcu@...r.kernel.org, rdunlap@...radead.org,
        rostedt@...dmis.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] WARNING in trc_read_check_handler

On Sat, Dec 04, 2021 at 10:50:47AM +0100, Dmitry Vyukov wrote:
> On Wed, 1 Dec 2021 at 22:09, Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > On Wed, Dec 01, 2021 at 12:50:07PM -0800, syzbot wrote:
> > > syzbot suspects this issue was fixed by commit:
> > >
> > > commit 96017bf9039763a2e02dcc6adaa18592cd73a39d
> > > Author: Paul E. McKenney <paulmck@...nel.org>
> > > Date:   Wed Jul 28 17:53:41 2021 +0000
> > >
> > >     rcu-tasks: Simplify trc_read_check_handler() atomic operations
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1281d89db00000
> > > start commit:   5319255b8df9 selftests/bpf: Skip verifier tests that fail ..
> > > git tree:       bpf-next
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=9290a409049988d4
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=fe9d8c955bd1d0f02dc1
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14990477300000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=105ebd84b00000
> > >
> > > If the result looks correct, please mark the issue as fixed by replying with:
> >
> > #syz fix: rcu-tasks: Simplify trc_read_check_handler() atomic operations
> >
> > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> >
> > Give or take.  There were quite a few related bugs, so some or all of
> > the following commits might also have helped:
> >
> > cbe0d8d91415c rcu-tasks: Wait for trc_read_check_handler() IPIs
> > 18f08e758f34e rcu-tasks: Add trc_inspect_reader() checks for exiting critical section
> > 46aa886c483f5 rcu-tasks: Fix IPI failure handling in trc_wait_for_one_reader
> 
> Thanks for checking. If we don't have one exact fix, let's go with
> what syzbot suggested. At this point it does not matter much since all
> of them are in most trees I assume. We just need to close the bug with
> something.
> 
> #syz fix: rcu-tasks: Simplify trc_read_check_handler() atomic operations

Fair enough!

> > Quibbles aside, it is nice to get an automated email about having fixed
> > a bug as opposed to having added one.  ;-)
> 
> Yes, but one is not possible without the other :-)

But of course it is possible!  For example, syzkaller might find a bug
that was already fixed, and then before notifying me about the bug, you
see the fix.  For example, by failing to reproduce a mainline bug on -rcu.

Not that I particularly want to be auto-spammed about bugs that I have
already fixed, mind you!  ;-)

							Thanx, Paul