Subject: Re: WARNING: kobject bug in br_add_if

From: Hangbin Liu <[email-masked]>
Date: Thu, 26 Apr 2018 18:37:03 +0800

On Thu, Apr 26, 2018 at 10:04:16AM +0200, Dmitry Vyukov wrote:
> On Thu, Apr 26, 2018 at 8:13 AM, Hangbin Liu <[email-masked]> wrote:
> > On Wed, Apr 11, 2018 at 05:18:23PM +0200, Dmitry Vyukov wrote:
> >> On Wed, Apr 11, 2018 at 5:15 PM, syzbot
> >> <[email-masked]> wrote:
> >> > Hello,
> >> >
> >> > syzbot hit the following crash on upstream commit
> >> > 10b84daddbec72c6b440216a69de9a9605127f7a (Sat Mar 31 17:59:00 2018 +0000)
> >> > Merge branch 'perf-urgent-for-linus' of
> >> > git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> >> > syzbot dashboard link:
> >> > https://syzkaller.appspot.com/bug?extid=de73361ee4971b6e6f75
> >> >
> >> > So far this crash happened 4 times on net-next, upstream.
> >> > Unfortunately, I don't have any reproducer for this crash yet.
> >> > Raw console output:
> >> > https://syzkaller.appspot.com/x/log.txt?id=5007286875455488
> >> > Kernel config:
> >> > https://syzkaller.appspot.com/x/.config?id=-2760467897697295172
> >> > compiler: gcc (GCC) 7.1.1 20170620
> >> >
> >> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> >> > Reported-by: [email-masked]
> >> > It will help syzbot understand when the bug is fixed. See footer for
> >> > details.
> >> > If you forward the report, please keep this part and the footer.
> >>
> >> +Greg
> >>
> >> The plan is to remove this WARNING from kobject_add, if there are no objections.
> >
> > Hi Dmitry,
> >
> > For this bug, why should we remove the WARNING instead of adding a check in
> > br_add_if()? Something like
> 
> 
> Mainline because nobody wants to fix these.
> If you think this is a real bug and you are ready to fix it, please
> mail an official patch.
> 
> >> > ------------[ cut here ]------------
> >> > binder: 23650:23651 unknown command 1078223622
> >> > kobject_add_internal failed for brport (error: -12 parent: bond0)

Re-checked the error. This is a -ENOMEM. So normally we could ignore it.

But on the other hand, although we could find out the slave iface's
master in netdev_master_upper_dev_link(). It already go much further
and allocate some resource and change iface state. e.g.

[54273.968516] br0: port 1(em1) entered blocking state
[54273.973979] br0: port 1(em1) entered disabled state

So I think we'd better return as early as possible. I will post a fix
for this.

Thanks
Hangbin

> >> > binder: 23650:23651 ioctl c0306201 2000dfd0 returned -22
> >> > WARNING: CPU: 1 PID: 23647 at lib/kobject.c:242
> >> > kobject_add_internal+0x3f6/0xbc0 lib/kobject.c:240
> >> > Kernel panic - not syncing: panic_on_warn set ...
> >> >
> >> > CPU: 1 PID: 23647 Comm: syz-executor7 Not tainted 4.16.0-rc7+ #374
> >> > binder: BINDER_SET_CONTEXT_MGR already set
> >> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> >> > Google 01/01/2011
> >> > Call Trace:
> >> >  __dump_stack lib/dump_stack.c:17 [inline]
> >> >  dump_stack+0x194/0x24d lib/dump_stack.c:53
> >> >  panic+0x1e4/0x41c kernel/panic.c:183
> >> >  __warn+0x1dc/0x200 kernel/panic.c:547
> >> >  report_bug+0x1f4/0x2b0 lib/bug.c:186
> >> >  fixup_bug.part.10+0x37/0x80 arch/x86/kernel/traps.c:178
> >> >  fixup_bug arch/x86/kernel/traps.c:247 [inline]
> >> >  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
> >> >  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
> >> >  invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:986
> >> > RIP: 0010:kobject_add_internal+0x3f6/0xbc0 lib/kobject.c:240
> >> > RSP: 0018:ffff8801d089f560 EFLAGS: 00010286
> >> > RAX: dffffc0000000008 RBX: ffff8801adbee178 RCX: ffffffff815b193e
> >> > RDX: 0000000000040000 RSI: ffffc900022aa000 RDI: 1ffff1003a113e31
> >> > RBP: ffff8801d089f658 R08: 1ffff1003a113df3 R09: 0000000000000000
> >> > R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff1003a113eb2
> >> > R13: 00000000fffffff4 R14: ffff8801abd88828 R15: ffff8801d75a1e00
> >> >  kobject_add_varg lib/kobject.c:364 [inline]
> >> >  kobject_init_and_add+0xf9/0x150 lib/kobject.c:436
> >> >  br_add_if+0x79a/0x1a70 net/bridge/br_if.c:533
> >> >  add_del_if+0xf4/0x140 net/bridge/br_ioctl.c:101
> >> >  br_dev_ioctl+0xa2/0xc0 net/bridge/br_ioctl.c:396
> >> >  dev_ifsioc+0x333/0x9b0 net/core/dev_ioctl.c:334
> >> >  dev_ioctl+0x176/0xbe0 net/core/dev_ioctl.c:500
> >> >  sock_do_ioctl+0x1ba/0x390 net/socket.c:981
> >> >  sock_ioctl+0x367/0x670 net/socket.c:1081
> >> >  vfs_ioctl fs/ioctl.c:46 [inline]
> >> >  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
> >> >  SYSC_ioctl fs/ioctl.c:701 [inline]
> >> >  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
> >> >  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
> >> >  entry_SYSCALL_64_after_hwframe+0x42/0xb7
> >> > RIP: 0033:0x454e79
> >> > RSP: 002b:00007eff7dab7c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> >> > RAX: ffffffffffffffda RBX: 00007eff7dab86d4 RCX: 0000000000454e79
> >> > RDX: 0000000020000000 RSI: 00000000000089a2 RDI: 0000000000000014
> >> > RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
> >> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000015
> >> > R13: 0000000000000369 R14: 00000000006f7278 R15: 0000000000000006
> >> > Dumping ftrace buffer:
> >> >    (ftrace buffer empty)
> >> > Kernel Offset: disabled
> >> > Rebooting in 86400 seconds..