Re: 2.6.23-mm1 - list_add corruption in cgroup

[Cedric Le Goater <clg@fr.ibm.com>]

Hello !

While polling the contents of a cgroup task file, I caught the 
following corruption. Is there a known race (and a fix) or should 
I start digging ? 

the program running in the cgroup is fork/exec intensive:

 while (1) {
        int i, s;    
    
        for (i = 0; i < count; i++)
            if (fork() == 0) 
                execlp("/bin/true", "true", 0);
        
        for (i = 0; i < count; i++) 
            wait(&s);
    }

Thanks for any insights, 

C. 



 list_add corruption. next->prev should be prev (ffffffff80a3f338), but was 0000000000200200. (next=ffff810103dcbe90).
------------[ cut here ]------------
kernel BUG at /home/legoater/linux/2.6.23-mm1/lib/list_debug.c:27!
invalid opcode: 0000 [1] SMP 
last sysfs file: /devices/pci0000:00/0000:00:1e.0/0000:01:01.0/local_cpus
CPU 3 
Modules linked in: ipt_REJECT iptable_filter autofs4 nfs lockd sunrpc tg3 sg joydev ext3 jbd ehci_hcd ohci_hcd uhci_hcd
Pid: 2441, comm: bash Not tainted 2.6.23-mm1 #4
RIP: 0010:[<ffffffff80308cda>]  [<ffffffff80308cda>] __list_add+0x27/0x5b
RSP: 0018:ffff810103d87dd8  EFLAGS: 00010296
RAX: 0000000000000079 RBX: ffff810105033040 RCX: 0000000000000079
RDX: ffff810103d960c0 RSI: 0000000000000001 RDI: 0000000000000096
RBP: ffff810103d87dd8 R08: 0000000000000002 R09: ffff810008123780
R10: 0000000000000000 R11: ffff810103d87a98 R12: 0000000000000000
R13: ffff810105033040 R14: ffff810104c11ac0 R15: 0000000000000000
FS:  00007f4e273556f0(0000) GS:ffff81010011a840(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00000000006ca2f8 CR3: 0000000103d82000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process bash (pid: 2441, threadinfo ffff810103d86000, task ffff810103d960c0)
last branch before last exception/interrupt
 from  [<ffffffff80235885>] printk+0x68/0x69
 to  [<ffffffff80308cda>] __list_add+0x27/0x5b
Stack:  ffff810103d87de8 ffffffff80308d1a ffff810103d87e08 ffffffff802606bf
 ffff810103d87e08 0000000000000000 ffff810103d87ea8 ffffffff80233dca
 ffff810103ddf340 00007f4e27355780 0000000000000000 ffff810103d87f58
Call Trace:
 [<ffffffff80308d1a>] list_add+0xc/0xe
 [<ffffffff802606bf>] cgroup_post_fork+0x41/0x52
 [<ffffffff80233dca>] copy_process+0x12d0/0x143a
 [<ffffffff8020b9b5>] tracesys+0xdc/0xe1
 [<ffffffff80234095>] do_fork+0x76/0x203
 [<ffffffff802679cc>] audit_syscall_entry+0x148/0x17e
 [<ffffffff8020b9b5>] tracesys+0xdc/0xe1
 [<ffffffff80209dd5>] sys_clone+0x23/0x25
 [<ffffffff8020bb67>] ptregscall_common+0x67/0xb0

INFO: lockdep is turned off.

Code: 0f 0b eb fe 4c 8b 00 49 39 f0 74 18 48 89 c1 4c 89 c2 48 c7 
RIP  [<ffffffff80308cda>] __list_add+0x27/0x5b
 RSP <ffff810103d87dd8>
BUG: soft lockup - CPU#1 stuck for 11s! [true:2030]
CPU 1:
Modules linked in: ipt_REJECT iptable_filter autofs4 nfs lockd sunrpc tg3 sg joydev ext3 jbd ehci_hcd ohci_hcd uhci_hcd
Pid: 2030, comm: true Tainted: G      D 2.6.23-mm1 #4
RIP: 0010:[<ffffffff80306baf>]  [<ffffffff80306baf>] __write_lock_failed+0xf/0x20
RSP: 0018:ffff81010513be80  EFLAGS: 00000287
RAX: 0000000000000001 RBX: ffff81010513be98 RCX: ffffffff807d8d60
RDX: 0000000000000037 RSI: 0000000000000037 RDI: ffffffff805beac0
RBP: ffff81010289e040 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff8026072c R11: ffff81010513be08 R12: ffff81000812c300
R13: ffff81010289e040 R14: ffff81010513a000 R15: ffff810087acb000
FS:  0000000000000000(0000) GS:ffff8101000560c0(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007f8171b028b0 CR3: 0000000000201000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400

Call Trace:
 [<ffffffff80308a1d>] _raw_write_lock+0x6c/0x8b
 [<ffffffff8026072c>] cgroup_exit+0x5c/0xc3
 [<ffffffff80474803>] _write_lock+0x2d/0x31
 [<ffffffff8026072c>] cgroup_exit+0x5c/0xc3
 [<ffffffff802383c1>] do_exit+0x2a0/0x7a5
 [<ffffffff80238955>] sys_exit_group+0x0/0x14
 [<ffffffff80238967>] sys_exit_group+0x12/0x14
 [<ffffffff8020b9b5>] tracesys+0xdc/0xe1
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