layered nfs mounts - lockmgr panic

["Vincent Labrecque" <vnc@xxxxxxx>]

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Hi,

Under Dragonfly-Preview (as of 3 days ago), mounting anything over
an
nfs mount crashes.  I first stumbled upon this with 2 layered nfs
mounts, like so:

# mount_nfs -3 -s -i rasid:/safe/muz /muz
# ls /muz
main rip vnc
# ls /muz/main
^C
# mount_nfs -3 -s -i rasid:/safe/muz /muz
panic: lockmgr: locking against myself
Trace beginning at frame 0xcf0c7a38
panic(c054d6c6,c0616ac0,c057dcf4,cf0c7a68,0) at panic+0x99
panic(c057dcf4,c10c5bc0,10,133f,0) at panic+0x99
lockmgr(cf35c5cc,2,2,cf35c530,c13964c0) at lockmgr+0x365
vn_lock(cf35c530,2,cf35c530,c13967e4,cf0c7af4) at vn_lock+0x21
vget(cf35c530,2,1c,0,0) at vget+0x33
nfs_nget(c13964c0,cf3c4cd0,1c,cf0c7b0c,0) at nfs_nget+0xc3
nfs_root(c13964c0,cf0c7b9c,cf0c7ba4,c061b648,c061b648) at
nfs_root+0x38
checkdirs(cf35c530,c13967e4,0,c11c6c78,c11c6c78) at checkdirs+0x2f
sys_mount(cf0c7cf4,cf0c7d04,10,cf64eb900,0) at sys_mount+0x844
syscall2(2f,2f,2f,2,bfbff738) at syscall2+0x20e
Xint0x80_syscall() at Xint0x80_syscall0x2a
Debugger("panic")
Stopped at Debugger+0x44: movb $0,in_Debugger.0
ddb>

Isolating the problem further I found:
      * mounting anything over a nfs partition triggers the same
crash,
      * mounting nfs over a local partition does not crash,

Sorry for the possible typos, this is entirely reproductible, so I
can
test patches and play around in ddb if it helps to debug it.
However
the machine is not very fast so it _will_ take a while to get test
results if you cannot reproduce it.

I have only restarted following DragonFly development, so forgive
me if
I could have known that this was fixed in -HEAD.

I am sending this as a pre-bug report.  I am now initiating the
build of
an -HEAD kernel to see if it was fixed.  I should be able to report
on
this within an hour or so. [update: I will have to update the
toolchain before i can build the kernel.  So expect to wait until
tomorrow for -HEAD results. Though I can interrupt the build and
test diffs - no problem)

- --Vincent
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