[Users] Infinite loop in __d_lookup ?

[Jakob Goldbach]

Hi,

I regularly have processes that gets stock eating all cpu. SysRq-p says
it is stock in __d_lookup+0x10b as seen in dmesg output below.

I run vanilla 2.6.18 with 028stab053 and the lustre filesystem. I also
run lustre on non-openvz kernel without problems, hence this mail to
this group. 

I believe I've found where the problem is, but I'm not a kernel hacker
so I don't know what to do about this information. 

I'd appreciate any hints on what to do next to get this solved.

Below is what I could find out. 

Thanks,
Jakob 

gdb find that the process is in the hlist_for_each_entry_rcu loop:

(gdb) list *__d_lookup+0x10b
0x12f0 is in __d_lookup (fs/dcache.c:1153).
1148            struct dentry *dentry, *found;
1149
1150            rcu_read_lock();
1151
1152            found = NULL;
1153            hlist_for_each_entry_rcu(dentry, node, head, d_hash) {
1154                    struct qstr *qstr;
1155
1156                    if (dentry->d_name.hash != hash)
1157                            continue;

I believe this is the relevant part (0x12f0) of the disassembled object:
 
    12e0:       4d 8b 24 24             mov    (%r12),%r12
    12e4:       4d 85 e4                test   %r12,%r12
    12e7:       74 2c                   je     1315 <__d_lookup+0x130>
    12e9:       49 8b 04 24             mov    (%r12),%rax
    12ed:       0f 18 08                prefetcht0 (%rax)
    12f0:       49 8d 5c 24 d8          lea    0xffffffffffffffd8(%r12),
%rbx
    12f5:       8b 45 cc                mov    0xffffffffffffffcc(%rbp),
%eax
    12f8:       39 43 40                cmp    %eax,0x40(%rbx)
    12fb:       75 e3                   jne    12e0 <__d_lookup+0xfb>


Dmesg after sysrq-p:




[186124.494329] SysRq: Show Regs
[186124.495218] ----------- IPI show regs -----------
[186124.496136] CPU 3, VCPU 0:1
[186124.496804] Modules linked in: simfs vznetdev vzethdev vzrst ip_nat
vzcpt ip_conntrack nfnetlink vzdquota vzmon vzdev xt_length ipt_ttl xt_
tcpmss ipt_TCPMSS iptable_mangle xt_multiport xt_limit ipt_tos
ipt_REJECT iptable_filter ip_tables x_tables 8021q osc mgc lustre lov
lquota mdc
 ksocklnd ptlrpc obdclass lnet lvfs libcfs bonding xfs
[186124.503636] Pid: 22699, comm: find Not tainted
2.6.18.8-openvz-028stab053-bnx2-1.6.7b-arpannounce1 #3 028stab053
[186124.505535] RIP: 0060:[<ffffffff8029b314>]  [<ffffffff8029b314>]
__d_lookup+0x10b/0x142
[186124.507265] RSP: 0068:ffff810073d63bc8  EFLAGS: 00000282
[186124.508296] RAX: ffff8101016dc298 RBX: ffff8101016dc270 RCX:
0000000000000013
[186124.509768] RDX: 0000000000025ff5 RSI: 00c38320c56a5ff5 RDI:
ffff810118b056b0
[186124.511480] RBP: ffff810073d63c08 R08: ffff8100ac9e8000 R09:
ffff810118b056b0
[186124.512963] R10: 0000000000000000 R11: 0000000000000000 R12:
ffff8101016dc298
[186124.514452] R13: ffff810073d63e38 R14: ffff810118b056b0 R15:
ffff810073d63c78
[186124.515931] FS:  00002ba786cb56d0(0000) GS:ffff81012a693340(0000)
knlGS:0000000000000000
[186124.517538] CS:  0060 DS: 0000 ES: 0000 CR0: 0000000080050033
[186124.518587] CR2: 0000000000539938 CR3: 0000000073f06000 CR4:
00000000000006e0
[186124.520022] 
[186124.520023] Call Trace:
[186124.521245]  [<ffffffff8029105d>] do_lookup+0x2c/0x193
[186124.522363]  [<ffffffff80293122>] __link_path_walk+0xb07/0x10ac
[186124.523642]  [<ffffffff8029374e>] link_path_walk+0x87/0x140
[186124.524818]  [<ffffffff80293c76>] do_path_lookup+0x2d3/0x2f8
[186124.526000]  [<ffffffff802945e2>] __user_walk_fd+0x41/0x62
[186124.527156]  [<ffffffff8028cecb>] vfs_lstat_fd+0x24/0x5a
[186124.528278]  [<ffffffff8028cf23>] sys_newlstat+0x22/0x3c
[186124.529383]  [<ffffffff80209902>] system_call+0x7e/0x83
[186124.530362] DWARF2 unwinder stuck at system_call+0x7e/0x83
[186124.531460] Leftover inexact backtrace:
[186124.532563]