Sv: Re: [Users] Infinite loop in __d_lookup ?
Pavel Emelyanov
xemul at openvz.org
Thu May 15 12:21:49 EDT 2008
Jakob Goldbach wrote:
> That would be great. Thanks.There are usually a few days between it gets stuck.
Ok. Happily, I've managed to invent what I need to check first
before it's too late here in Moscow ;)
I presume, that the infinite loop is really somewhere near the
__d_lookup. Please, apply this patch in attach (I made it against
2.6.18-028stab053.5, but should fit OK all the other 028stab053
releases) and check for warnings in dmesg ;)
Let's see whether this is really __d_lookup.
> /jakob
> - oprindelig besked -
> Emne: Re: [Users] Infinite loop in __d_lookup ?
> Fra: Pavel Emelyanov <xemul at openvz.org>
> Dato: 15-05-2008 12:34
>
> Jakob Goldbach wrote:
>> 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.
>
> If you can reproduce this in a reasonable time I can send you
> a debugging patch to find out what's going on there.
>
> Let's try with it?
>
>> 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]
>>
>>
>> _______________________________________________
>> Users mailing list
>> Users at openvz.org
>> https://openvz.org/mailman/listinfo/users
>>
>
>
>
>
-------------- next part --------------
--- ./fs/dcache.c.loopdebug 2008-05-15 20:09:04.000000000 +0400
+++ ./fs/dcache.c 2008-05-15 20:16:19.000000000 +0400
@@ -1128,12 +1128,24 @@ struct dentry * d_lookup(struct dentry *
{
struct dentry * dentry = NULL;
unsigned long seq;
+ unsigned long loops = 0;
+ static int once = 1;
do {
seq = read_seqbegin(&rename_lock);
dentry = __d_lookup(parent, name);
if (dentry)
break;
+
+ if (loops++ > 200) {
+ printk("%s: Abort on 200 seq-retry iteration\n",
+ __func__);
+ if (once) {
+ once = 0;
+ dump_stack();
+ }
+ break;
+ }
} while (read_seqretry(&rename_lock, seq));
return dentry;
}
@@ -1146,6 +1158,8 @@ struct dentry * __d_lookup(struct dentry
struct hlist_head *head = d_hash(parent,hash);
struct hlist_node *node;
struct dentry *dentry, *found;
+ unsigned long loops = 0;
+ static int once = 1;
rcu_read_lock();
@@ -1154,9 +1168,9 @@ struct dentry * __d_lookup(struct dentry
struct qstr *qstr;
if (dentry->d_name.hash != hash)
- continue;
+ goto next_nolock;
if (dentry->d_parent != parent)
- continue;
+ goto next_nolock;
spin_lock(&dentry->d_lock);
@@ -1193,6 +1207,16 @@ struct dentry * __d_lookup(struct dentry
break;
next:
spin_unlock(&dentry->d_lock);
+next_nolock:
+ if (loops++ > 5000) {
+ printk("%s: Abort on 5000 loop iteration in a chain\n",
+ __func__);
+ if (once) {
+ once = 0;
+ dump_stack();
+ }
+ break;
+ }
}
rcu_read_unlock();
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