reproducible panic with mount_smbfs

Attilio Rao attilio at
Sun Nov 2 08:05:10 PST 2008

2008/11/2, Yuri Pankov <yuri.pankov at>:
> Hi,
>  Trying to mount nonexistent smb share with mount_smbfs leads to
>  following panic:
>  # mount_smbfs //yuri at lifebane/blahblah /mnt
>  Unread portion of the kernel message buffer:
>  smb_co_lock: recursive lock for object 1
>  panic: Lock (lockmgr) smb_vc not locked @
>  /usr/src/sys/modules/smbfs/../../netsmb/smb_conn.c:329.
>  cpuid = 0
>  KDB: stack backtrace:
>  db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
>  panic() at panic+0x182
>  witness_assert() at witness_assert+0x21a
>  __lockmgr_args() at __lockmgr_args+0x17a
>  smb_co_put() at smb_co_put+0x76
>  smb_sm_lookup() at smb_sm_lookup+0xfe
>  smb_usr_lookup() at smb_usr_lookup+0xcd
>  nsmb_dev_ioctl() at nsmb_dev_ioctl+0x1f6
>  giant_ioctl() at giant_ioctl+0x75
>  devfs_ioctl_f() at devfs_ioctl_f+0x76
>  kern_ioctl() at kern_ioctl+0x92
>  ioctl() at ioctl+0xfd
>  syscall() at syscall+0x1bf
>  Xfast_syscall() at Xfast_syscall+0xab
>  --- syscall (54, FreeBSD ELF64, ioctl), rip = 0x800939aec, rsp =
>  0x7fffffffe038, rbp = 0x7fffffffe450 ---
>  Uptime: 6m46s
>  Physical memory: 2032 MB

So, what is happening here is that smb_co_lock() is AFU.
Infact looking at the code:
smb_co_lock(struct smb_connobj *cp, int flags, struct thread *td)
        if (smb_co_lockstatus(cp, td) == LK_EXCLUSIVE &&
            (flags & LK_CANRECURSE) == 0) {
                SMBERROR("recursive lock for object %d\n", cp->co_level);
                return 0;

from that it is obvious that smb_co_lock() won't recurse the lock
really, but will let believe the consumer it acquired the lock
successfully without panicking at all (the printf is like a little
joke there).
I think that we don't panic here mainly because these are "user
driver" events and we want avoid to get a DoS for the kernel but it is
an unacceptable code also.

This can be fixed by allowing recuring lockmgr by default but the
problem is more vaste.
For example, it would be very nice to drop the LK_DRAIN support from
netsmb in order to completely remove it from the 8.0 kernel serie and
kill a bogus / dangerous option for lockmgr. It would be a cornerstone
for lockmgr wealth really.

What really is missing here is a valid netsmb maintainer, someone that
knows well the layers involved, is motivated to work on it and can
take advantage from the other kernel developer experience on the most
hardcore parts.
It would be also nice, for example, to bring in some Apple's changes
(like the crypto support).

Someone willing to step in would be very appreciated.


Peace can only be achieved by understanding - A. Einstein

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