netdev - Re: WARNING in kernfs_add

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Date:   Mon, 7 May 2018 11:33:33 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        linux-wireless@...r.kernel.org,
        Eric Dumazet <eric.dumazet@...il.com>,
        netdev <netdev@...r.kernel.org>,
        syzbot <syzbot+df47f81c226b31d89fb1@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: WARNING in kernfs_add_one

On Mon, May 7, 2018 at 10:43 AM, Johannes Berg
<johannes@...solutions.net> wrote:
> On Sat, 2018-05-05 at 15:07 -0700, Greg KH wrote:
>
>> > > > syzbot found the following crash on:
>
> Maybe it should learn to differentiate warnings, if it's going to set
> panic_on_warn :-)

How?
Note that this is not specific to syzbot. If you see WARNINGs in a
subsystem that you have no idea about (or you just a normal user),
what do you do? Right, you report it to maintainers.


> I get why, but still, at least differentiating in the emails wouldn't be
> bad.

Well, the subject says "WARNING".
But note there are _very_ bad WARNINGs too. Generally, a WARNING means
a kernel bug just that kernel can tolerate without bringing the system
down (as opposed to BUG).


>> > > > kernfs: ns required in 'ieee80211' for 'phy3'
>
> Huh. What does that even mean?
>
>> > > > RIP: 0010:kernfs_add_one+0x406/0x4d0 fs/kernfs/dir.c:758
>> > > > RSP: 0018:ffff8801ca9eece0 EFLAGS: 00010286
>> > > > RAX: 000000000000002d RBX: ffffffff87d5cee0 RCX: ffffffff8160ba7d
>> > > > RDX: 0000000000000000 RSI: ffffffff81610731 RDI: ffff8801ca9ee840
>> > > > RBP: ffff8801ca9eed20 R08: ffff8801d9538500 R09: 0000000000000006
>> > > > R10: ffff8801d9538500 R11: 0000000000000000 R12: ffff8801ad1cb6c0
>> > > > R13: ffffffff885da640 R14: 0000000000000020 R15: 0000000000000000
>> > > >  kernfs_create_link+0x112/0x180 fs/kernfs/symlink.c:41
>> > > >  sysfs_do_create_link_sd.isra.2+0x90/0x130 fs/sysfs/symlink.c:43
>> > > >  sysfs_do_create_link fs/sysfs/symlink.c:79 [inline]
>> > > >  sysfs_create_link+0x65/0xc0 fs/sysfs/symlink.c:91
>> > > >  device_add_class_symlinks drivers/base/core.c:1612 [inline]
>> > > >  device_add+0x7a0/0x16d0 drivers/base/core.c:1810
>> > > >  wiphy_register+0x178a/0x2430 net/wireless/core.c:806
>> > > >  ieee80211_register_hw+0x13cd/0x35d0 net/mac80211/main.c:1047
>> > > >  mac80211_hwsim_new_radio+0x1d9b/0x3410
>> > > > drivers/net/wireless/mac80211_hwsim.c:2772
>> > > >  hwsim_new_radio_nl+0x7a7/0xa60 drivers/net/wireless/mac80211_hwsim.c:3246
>> > > >  genl_family_rcv_msg+0x889/0x1120 net/netlink/genetlink.c:599
>
> Basically we're creating a new virtual radio, which in turn creates a
> new device, which we have to register.
>
> Something is going on with the context here that makes sysfs unhappy,
> but TBH I have no idea what.
>
> johannes
>
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