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Date:   Mon, 18 Nov 2019 19:54:10 -0800
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Marco Elver <elver@google.com>,
        syzbot <syzbot+08f3e9d26e5541e1ecf2@syzkaller.appspotmail.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Josh Triplett <josh@joshtriplett.org>, axboe@kernel.dk,
        justin@coraid.com, linux-block@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller-bugs@googlegroups.com
Subject: Re: KCSAN: data-race in process_srcu / synchronize_srcu
Message-ID: <20191119035410.GR2889@paulmck-ThinkPad-P72>
Reply-To: paulmck@kernel.org
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On Mon, Nov 18, 2019 at 06:48:05PM -0800, Eric Biggers wrote:
> On Mon, Nov 04, 2019 at 08:53:03AM -0800, Paul E. McKenney wrote:
> > On Mon, Nov 04, 2019 at 05:14:50PM +0100, Marco Elver wrote:
> > > On Mon, 4 Nov 2019 at 17:11, Paul E. McKenney <paulmck@kernel.org> wrote:
> > > >
> > > > On Mon, Nov 04, 2019 at 12:31:56PM +0100, Marco Elver wrote:
> > > > > +RCU folks, since this is probably a data race in RCU.
> > > > >
> > > > > On Mon, 4 Nov 2019 at 12:29, syzbot
> > > > > <syzbot+08f3e9d26e5541e1ecf2@syzkaller.appspotmail.com> wrote:
> > > > > >
> > > > > > Hello,
> > > > > >
> > > > > > syzbot found the following crash on:
> > > > > >
> > > > > > HEAD commit:    05f22368 x86, kcsan: Enable KCSAN for x86
> > > > > > git tree:       https://github.com/google/ktsan.git kcsan
> > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=17ade7ef600000
> > > > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
> > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=08f3e9d26e5541e1ecf2
> > > > > > 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+08f3e9d26e5541e1ecf2@syzkaller.appspotmail.com
> > > > > >
> > > > > > ==================================================================
> > > > > > BUG: KCSAN: data-race in process_srcu / synchronize_srcu
> > > > > >
> > > > > > write to 0xffffffff8604e8a0 of 8 bytes by task 17 on cpu 1:
> > > > > >   srcu_gp_end kernel/rcu/srcutree.c:533 [inline]
> > > > > >   srcu_advance_state kernel/rcu/srcutree.c:1146 [inline]
> > > > > >   process_srcu+0x207/0x780 kernel/rcu/srcutree.c:1237
> > > > > >   process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
> > > > > >   worker_thread+0xa0/0x800 kernel/workqueue.c:2415
> > > > > >   kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
> > > > > >   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
> > > > > >
> > > > > > read to 0xffffffff8604e8a0 of 8 bytes by task 12515 on cpu 0:
> > > > > >   srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline]
> > > > > >   synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996
> > > > > >   fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164
> > > > > >   process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
> > > > > >   worker_thread+0xa0/0x800 kernel/workqueue.c:2415
> > > > > >   kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
> > > > > >   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
> > > > > >
> > > > > > Reported by Kernel Concurrency Sanitizer on:
> > > > > > CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0
> > > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > > > > > Google 01/01/2011
> > > > > > Workqueue: events_unbound fsnotify_connector_destroy_workfn
> > > > > > ==================================================================
> > > > > > Kernel panic - not syncing: panic_on_warn set ...
> > > > > > CPU: 0 PID: 12515 Comm: kworker/u4:8 Not tainted 5.4.0-rc3+ #0
> > > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > > > > > Google 01/01/2011
> > > > > > Workqueue: events_unbound fsnotify_connector_destroy_workfn
> > > > > > Call Trace:
> > > > > >   __dump_stack lib/dump_stack.c:77 [inline]
> > > > > >   dump_stack+0xf5/0x159 lib/dump_stack.c:113
> > > > > >   panic+0x210/0x640 kernel/panic.c:221
> > > > > >   kcsan_report.cold+0xc/0x10 kernel/kcsan/report.c:302
> > > > > >   __kcsan_setup_watchpoint+0x32e/0x4a0 kernel/kcsan/core.c:411
> > > > > >   __tsan_read8 kernel/kcsan/kcsan.c:36 [inline]
> > > > > >   __tsan_read8+0x2c/0x30 kernel/kcsan/kcsan.c:36
> > > > > >   srcu_might_be_idle kernel/rcu/srcutree.c:784 [inline]
> > > > > >   synchronize_srcu+0x107/0x214 kernel/rcu/srcutree.c:996
> > > > > >   fsnotify_connector_destroy_workfn+0x63/0xb0 fs/notify/mark.c:164
> > > > > >   process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
> > > > > >   worker_thread+0xa0/0x800 kernel/workqueue.c:2415
> > > > > >   kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
> > > > > >   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352
> > > > > > Kernel Offset: disabled
> > > > > > Rebooting in 86400 seconds..
> > > > > >
> > > > > >
> > > > > > ---
> > > > > > This bug is generated by a bot. It may contain errors.
> > > > > > See https://goo.gl/tpsmEJ for more information about syzbot.
> > > > > > syzbot engineers can be reached at syzkaller@googlegroups.com.
> > > > > >
> > > > > > syzbot will keep track of this bug report. See:
> > > > > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > > >
> > > > Good catch!  Does the patch below help?
> > > 
> > > Looks good to me, thanks for the quick fix.
> > > 
> > > Acked-by: Marco Elver <elver@google.com>
> > 
> > Applied, thank you!
> > 
> > 							Thanx, Paul
> 
> This patch is not in linux-next.  What happened to it?

It is in -rcu, but arrived too late to make my pull request for
v5.5.  It will hit -next shortly after v5.5-rc1.

							Thanx, Paul