Re: [syzbot] [net?] possible deadlock in rtnl_lock (8)

[D. Wythe]

On 9/10/24 2:36 PM, Eric Dumazet wrote:
> On Tue, Sep 10, 2024 at 7:55 AM D. Wythe <alibuda@xxxxxxxxxxxxxxxxx> wrote:
> > On 9/9/24 7:44 PM, Wenjia Zhang wrote:
> > > On 09.09.24 10:02, Eric Dumazet wrote:
> > > > On Sun, Sep 8, 2024 at 10:12 AM syzbot
> > > > <syzbot+51cf7cc5f9ffc1006ef2@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > > > > syzbot has found a reproducer for the following issue on:
> > > > >
> > > > > HEAD commit:    df54f4a16f82 Merge branch 'for-next/core' into
> > > > > for-kernelci
> > > > > git tree:
> > > > > git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
> > > > > for-kernelci
> > > > > console output:
> > > > > https://syzkaller.appspot.com/x/log.txt?x=12bdabc7980000
> > > > > kernel config:
> > > > > https://syzkaller.appspot.com/x/.config?x=dde5a5ba8d41ee9e
> > > > > dashboard link:
> > > > > https://syzkaller.appspot.com/bug?extid=51cf7cc5f9ffc1006ef2
> > > > > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils
> > > > > for Debian) 2.40
> > > > > userspace arch: arm64
> > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1798589f980000
> > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10a30e00580000
> > > > >
> > > > > Downloadable assets:
> > > > > disk image:
> > > > > https://storage.googleapis.com/syzbot-assets/aa2eb06e0aea/disk-df54f4a1.raw.xz
> > > > > vmlinux:
> > > > > https://storage.googleapis.com/syzbot-assets/14728733d385/vmlinux-df54f4a1.xz
> > > > > kernel image:
> > > > > https://storage.googleapis.com/syzbot-assets/99816271407d/Image-df54f4a1.gz.xz
> > > > >
> > > > > IMPORTANT: if you fix the issue, please add the following tag to the
> > > > > commit:
> > > > > Reported-by: syzbot+51cf7cc5f9ffc1006ef2@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > > >
> > > > > ======================================================
> > > > > WARNING: possible circular locking dependency detected
> > > > > 6.11.0-rc5-syzkaller-gdf54f4a16f82 #0 Not tainted
> > > > > ------------------------------------------------------
> > > > > syz-executor272/6388 is trying to acquire lock:
> > > > > ffff8000923b6ce8 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x20/0x2c
> > > > > net/core/rtnetlink.c:79
> > > > >
> > > > > but task is already holding lock:
> > > > > ffff0000dc408a50 (&smc->clcsock_release_lock){+.+.}-{3:3}, at:
> > > > > smc_setsockopt+0x178/0x10fc net/smc/af_smc.c:3064
> > > > >
> > > > > which lock already depends on the new lock.
> > I have noticed this issue for a while, but I question the possibility of
> > it. If I understand correctly, a deadlock issue following is reported here:
> >
> > #2
> > lock_sock_smc
> > {
> >       clcsock_release_lock            --- deadlock
> >       {
> >
> >       }
> > }
> >
> > #1
> > rtnl_mutex
> > {
> >       lock_sock_smc
> >       {
> >
> >       }
> > }
> >
> > #0
> > clcsock_release_lock
> > {
> >       rtnl_mutex                      --deadlock
> >       {
> >
> >       }
> > }
> >
> > This is of course a deadlock, but #1 is suspicious.
> >
> > How would this happen to a smc sock?
> >
> > #1 ->
> >          lock_sock_nested+0x38/0xe8 net/core/sock.c:3543
> >          lock_sock include/net/sock.h:1607 [inline]
> >          sockopt_lock_sock net/core/sock.c:1061 [inline]
> >          sockopt_lock_sock+0x58/0x74 net/core/sock.c:1052
> >          do_ip_setsockopt+0xe0/0x2358 net/ipv4/ip_sockglue.c:1078
> >          ip_setsockopt+0x34/0x9c net/ipv4/ip_sockglue.c:1417
> >          raw_setsockopt+0x7c/0x2e0 net/ipv4/raw.c:845
> >          sock_common_setsockopt+0x70/0xe0 net/core/sock.c:3735
> >          do_sock_setsockopt+0x17c/0x354 net/socket.c:2324
> >
> > As a comparison, the correct calling chain should be:
> >
> >          sock_common_setsockopt+0x70/0xe0 net/core/sock.c:3735
> >          smc_setsockopt+0x150/0xcec net/smc/af_smc.c:3072
> >          do_sock_setsockopt+0x17c/0x354 net/socket.c:2324
> >
> >
> > That's to say,  any setting on SOL_IP options of smc_sock will
> > go with smc_setsockopt, which will try lock clcsock_release_lock at first.
> >
> > Anyway, if anyone can explain #1, then we can see how to solve this problem,
> > otherwise I think this problem doesn't exist. (Just my opinion)
> Then SMC lacks some lockdep annotations.
>
> Please take a look at sock_lock_init_class_and_name() callers.

It seems so, which also explains why it wasn't reported with AF_SMC sock.
I'll try to fix it ASAP.

D. Wythe