linux-kernel - Re: [syzbot] [rdma?] INFO: task hung in add_one_compat

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Message-ID: <CANp29Y534CT0jqhp5LQi_ZCs=1_i4duRO=4CJ52by9ZDW-1Wfw@mail.gmail.com>
Date: Fri, 1 Nov 2024 16:55:32 +0100
From: Aleksandr Nogikh <nogikh@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: syzbot <syzbot+6dee15fdb0606ef7b6ba@...kaller.appspotmail.com>, leon@...nel.org, 
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org, 
	netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [rdma?] INFO: task hung in add_one_compat_dev (3)

Hi Jason,

On Tue, Oct 22, 2024 at 4:29 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> On Tue, Oct 22, 2024 at 12:39:27AM -0700, syzbot wrote:
>
> > 1 lock held by syz-executor/27959:
> >  #0: ffffffff8fcbffc8 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock net/core/rtnetlink.c:79 [inline]
> >  #0: ffffffff8fcbffc8 (rtnl_mutex){+.+.}-{3:3}, at: __rtnl_newlink net/core/rtnetlink.c:3749 [inline]
> >  #0: ffffffff8fcbffc8 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_newlink+0xab7/0x20a0 net/core/rtnetlink.c:3772
>
> There is really something wrong with the new sykzaller reporting, can
> someone fix it?
>
> The kernel log that shows the programs:
>
> https://syzkaller.appspot.com/x/log.txt?x=10d72727980000
>
> Doesn't have the word "newlink"/"new"/"link" etc, and yet there is an
> executor clearly sitting in a newlink netlink callback when we
> crashed.

These are likely coming from the network devices initialization code.
When syzbot spins up a new syz-executor, it creates a lot of
networking devices as one of the first steps.
https://github.com/google/syzkaller/blob/f00eed24f2a1332b07fef1a353a439133978d97b/executor/common_linux.h#L1482

So those syz-executors might have just been unable to start and then
they were abandoned (?)

>
> We need to see the syzkaller programs that are triggering these issues
> to get ideas, and for some reason they are missing now.

Once syzbot manages to find a reproducer, hopefully things will become
more clear.

-- 
Aleksandr

>
> Jason
>