On Sat, 2024-06-15 at 03:39 -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: cea2a26553ac mailmap: Add my outdated addresses to the map.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=169fd8ee980000 > kernel config: https://syzkaller.appspot.com/x/.config?x=fa0ce06dcc735711 > dashboard link: https://syzkaller.appspot.com/bug?extid=4207adf14e7c0981d28d > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/1f7ce933512f/disk-cea2a265.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/0ce3b9940616/vmlinux-cea2a265.xz > kernel image: https://storage.googleapis.com/syzbot-assets/19e24094ea37/bzImage-cea2a265.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+4207adf14e7c0981d28d@xxxxxxxxxxxxxxxxxxxxxxxxx > > INFO: task syz-executor.1:17770 blocked for more than 143 seconds. > Not tainted 6.10.0-rc3-syzkaller-00022-gcea2a26553ac #0 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:syz-executor.1 state:D stack:23800 pid:17770 tgid:17767 ppid:11381 flags:0x00000006 > Call Trace: > <TASK> > context_switch kernel/sched/core.c:5408 [inline] > __schedule+0x17e8/0x4a20 kernel/sched/core.c:6745 > __schedule_loop kernel/sched/core.c:6822 [inline] > schedule+0x14b/0x320 kernel/sched/core.c:6837 > schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894 > __mutex_lock_common kernel/locking/mutex.c:684 [inline] > __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752 > nfsd_nl_listener_get_doit+0x115/0x5d0 fs/nfsd/nfsctl.c:2124 > genl_family_rcv_msg_doit net/netlink/genetlink.c:1115 [inline] > genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] > genl_rcv_msg+0xb16/0xec0 net/netlink/genetlink.c:1210 > netlink_rcv_skb+0x1e5/0x430 net/netlink/af_netlink.c:2564 > genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 > netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline] > netlink_unicast+0x7ec/0x980 net/netlink/af_netlink.c:1361 > netlink_sendmsg+0x8db/0xcb0 net/netlink/af_netlink.c:1905 > sock_sendmsg_nosec net/socket.c:730 [inline] > __sock_sendmsg+0x223/0x270 net/socket.c:745 > ____sys_sendmsg+0x525/0x7d0 net/socket.c:2585 > ___sys_sendmsg net/socket.c:2639 [inline] > __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2668 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7f24ed27cea9 > RSP: 002b:00007f24ee0080c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e > RAX: ffffffffffffffda RBX: 00007f24ed3b3f80 RCX: 00007f24ed27cea9 > RDX: 0000000000000000 RSI: 0000000020000100 RDI: 0000000000000005 > RBP: 00007f24ed2ebff4 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > > > --- > This report 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@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > If the report is already addressed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want to overwrite report's subsystems, reply with: > #syz set subsystems: new-subsystem > (See the list of subsystem names on the web dashboard) > > If the report is a duplicate of another one, reply with: > #syz dup: exact-subject-of-another-report > > If you want to undo deduplication, reply with: > #syz undup We've had number of these reports recently. I think I understand what's happening but I'm not sure how to fix it. The problem manifests as a stuck nfsd_mutex: nfsd_nl_rpc_status_get_start takes the nfsd_mutex, and it's released in nfsd_nl_rpc_status_get_done. These are the ->start and ->done operations for the rpc_status_get dumpit routine. I think syzbot is triggering one of the two "goto errout_skb" conditions in netlink_dump (not sure which). In those cases we end up returning from that function without calling ->done, which would lead to the hung mutex like we see here. Is this a bug in the netlink code, or is the rpc_status_get dumpit routine not using ->start and ->done correctly? Thanks, -- Jeff Layton <jlayton@xxxxxxxxxx>
