BUG 797419 - xfs_iget goes recursive and dies a horrible death

[pv@xxxxxxxxxxxxx (lord@xxxxxxx)]

View Incident: 
http://co-op.engr.sgi.com/BugWorks/code/bwxquery.cgi?search=Search&wlong=1&view_type=Bug&wi=797419

Submitter : lord                      Submitter Domain : sgi.com            
Assigned Engineer : lord              Assigned Domain : sgi.com             
Assigned Group : xfs-linux            Category : software                   
Customer Reported : F                 Priority : 1                          
Project : xfs-linux                   Status : open                         
Description :
xfs_iget has some conditions where it can end up recalling itself,
this is allowed for, but there are cases in there where two threads
are looking up the same inode which it does not cope with, the end
result is usually this:

xfs_iget_core: ambiguous vns: vp/0xc3012b00, invp/0xc22c1800
Unable to handle kernel NULL pointer dereference at virtual address 00000008
 printing eip:
c889c115
*pde = 00000000

Entering kdb (0xc761e000) on processor 1 Panic: Oops
due to panic @ 0xc889c115
eax = 0x00000080 ebx = 0xc1750584 ecx = 0xc6103400 edx = 0x00000000 
esi = 0xc22c1800 edi = 0xc1750580 esp = 0xc761fb80 eip = 0xc889c115 
ebp = 0xc761fbfc  ss = 0x00000018  cs = 0x00000010 eflags = 0x00010282 
 ds = 0x00000018  es = 0x00000018 origeax = 0xffffffff &regs = 0xc761fb4c
[1]kdb> bt
    EBP       EIP         Function(args)
0xc761fbfc 0xc889c115 [xfs]vn_revalidate+0x19 (0xc22c1800, 0x80)
                               xfs .text 0xc8842060 0xc889c0fc 0xc889c1a0
0xc761fc50 0xc8871d6e [xfs]xfs_iget_core+0x706 (0xc22c1800, 0xc6103400, 0x0, 
0x403082, 0x0)
                               xfs .text 0xc8842060 0xc8871668 0xc8871d94
0xc761fc84 0xc8871dfa [xfs]xfs_vn_iget+0x2e (0xc22c1800, 0xc6103400, 0x0, 
0x403082, 0x0)
                               xfs .text 0xc8842060 0xc8871dcc 0xc8871e04
0xc761fcc4 0xc889be75 [xfs]vn_initialize+0xb9 (0xc7c91a00, 0xc22c1700, 0x1)
                               xfs .text 0xc8842060 0xc889bdbc 0xc889bee0
0xc761fcdc 0xc889ae7c [xfs]linvfs_read_inode+0x20 (0xc22c1700, 0xc22c1700)
                               xfs .text 0xc8842060 0xc889ae5c 0xc889aea4
0xc761fcf8 0xc014cfa4 get_new_inode+0xc4 (0xc6ab4000, 0x403082, 0xc1277170, 
0x0, 0x0)
                               kernel .text 0xc0100000 0xc014cee0 0xc014d038
0xc761fd24 0xc014d221 iget4+0xd9 (0xc6ab4000, 0x403082, 0x0, 0x0)
                               kernel .text 0xc0100000 0xc014d148 0xc014d22c
0xc761fd58 0xc889bfb8 [xfs]vn_get+0x28 (0xc3012b00, 0xc761fd98, 0x0)
                               xfs .text 0xc8842060 0xc889bf90 0xc889c07c
0xc761fdb0 0xc887184c [xfs]xfs_iget_core+0x1e4 (0x0, 0xc6103400, 0x0, 0x403082, 
0x0)
                               xfs .text 0xc8842060 0xc8871668 0xc8871d94
0xc761fde8 0xc8871dc1 [xfs]xfs_iget+0x2d (0xc6103400, 0x0, 0x403082, 0x0, 0x0)
                               xfs .text 0xc8842060 0xc8871d94 0xc8871dcc
0xc761fe58 0xc88883e3 [xfs]xfs_dir_lookup_int+0x143 (0x0, 0xc008a7e0, 0x5, 
0xc0ca7a80, 0xc761fee4)
                               xfs .text 0xc8842060 0xc88882a0 0xc8888570
[1]more> 
0xc761fea0 0xc888ca82 [xfs]xfs_lookup+0x96 (0xc008a7e0, 0xc0ca7a80, 0xc761fee0, 
0xc761fee4, 0x0)
                               xfs .text 0xc8842060 0xc888c9ec 0xc888caec
0xc761fef0 0xc8894ff4 [xfs]linvfs_lookup+0x70 (0xc0fdab60, 0xc0ca7a20)
                               xfs .text 0xc8842060 0xc8894f84 0xc8895040
0xc761ff18 0xc014335a real_lookup+0xa6 (0xc0db4040, 0xc761ff50, 0x0)
                               kernel .text 0xc0100000 0xc01432b4 0xc0143430
0xc761ff5c 0xc0143a1f path_walk+0x4e7 (0xc536212d, 0xc761ffa0)
                               kernel .text 0xc0100000 0xc0143538 0xc0143c60
0xc761ff7c 0xc0143fab __user_walk+0x6f (0x806efe8, 0x9, 0xc761ffa0, 0xc761e000)
                               kernel .text 0xc0100000 0xc0143f3c 0xc0144020
0xc761ffbc 0xc0140361 sys_stat64+0x3d (0x806efe8, 0xbffff884, 0x4010ad60, 
0x4000ae60, 0x806efe8)
                               kernel .text 0xc0100000 0xc0140324 0xc01403f4
           0xc010b610 system_call+0x34
                               kernel .text 0xc0100000 0xc010b5dc 0xc010b614