[Devel] Re: [PATCH] c/r: fix "scheduling in atomic" while restoring ipc shm

[Oren Laadan]

Nikita V. Youshchenko wrote:
>> Hi Nikita,
>>
>> Thanks for the report and the analysis. It actually helped to
>> pinpoint a couple of other minor issues in the code. This patch
>> should fix all of these.
>>
>> Oren.
> 
> Hi Oren.
> 
> With ckpt-v19 plus this patch applied, we still are getting a kernel
> crash, with BUG() fired at
> +       ipc = idr_find(&msg_ids->ipcs_idr, h->perms.id);
> +       BUG_ON(!ipc);
> added by the patch.
> 
> By looking at the code, I can't understand how this idr_find() can at
> all succeed, if the namespace it is looking in was just created and
> is empty.
> 
> What code adds object in question into this idr?

As Serge pointed out, the call to do_msgget(), if succeeded, should
have created the object, and if it didn't succeed then we would have
returned with an error message.

You can see in your log, that we request id 32769 (h->prems.id) and
that is what do_shmget() returned. So I'm quite confused...

Can you post your test program so I can try to reproduce it here ?
Also, can you add a debug output before and after the call to idr_find
that prints the h->perms.id ?

Thanks,

Oren.


> 
> Any hints?
> 


> Nikita
> 
> ...
> [   60.321860] [430:430:c/r:ckpt_read_obj_dispatch:254] type 502 len 120
> [   60.322489] [430:430:c/r:ckpt_read_obj:383] type 502 len 120(120,120)
> [   60.323140] [430:430:c/r:restore_ipc_shm:226] shm: do_shmget size 790528 flag 0x7a4 id 32769
> [   60.324257] [430:430:c/r:restore_ipc_shm:228] shm: do_shmget ret 32769
> [   60.325573] ------------[ cut here ]------------
> [   60.326059] kernel BUG at ipc/checkpoint_shm.c:274!
> [   60.326564] invalid opcode: 0000 [#1] PREEMPT SMP
> [   60.327124] last sysfs file:
> [   60.327480] Modules linked in:
> [   60.327903]
> [   60.328104] Pid: 430, comm: bash Not tainted 2.6.33-rc8 #2 /
> [   60.328104] EIP: 0060:[<c10e0abe>] EFLAGS: 00000246 CPU: 0
> [   60.328104] EIP is at restore_ipc_shm+0x1a0/0x35a
> [   60.328104] EAX: 00000000 EBX: 00000000 ECX: 00000005 EDX: c789ba58
> [   60.328104] ESI: 00008001 EDI: c793d640 EBP: c79ac000 ESP: c7991dbc
> [   60.328104]  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
> [   60.328104] Process bash (pid: 430, ti=c7990000 task=c7855b70 task.ti=c7990000)
> [   60.328104] Stack:
> [   60.328104]  c129da9c c79ac000 000c1000 00000000 c129db00 000001ae 000001b4 000c1000
> [   60.328104] <0> 00000000 c124dde1 000001ae 00000001 00000000 c7940c00 c79ac000 c10e036d
> [   60.328104] <0> 00000002 c129da9c ffffffef c129da9c c799ac60 c79ac000 c10e048a 000001f6
> [   60.328104] Call Trace:
> [   60.328104]  [<c10e036d>] ? restore_ipc_any+0xa5/0x119
> [   60.328104]  [<c10e048a>] ? restore_ipc_ns+0xa9/0x112
> [   60.328104]  [<c10e091e>] ? restore_ipc_shm+0x0/0x35a
> [   60.328104]  [<c10feb48>] ? restore_obj+0x98/0x116
> [   60.328104]  [<c11007ed>] ? ckpt_read_obj_dispatch+0x220/0x246
> [   60.328104]  [<c1100829>] ? ckpt_read_obj+0x16/0xe8
> [   60.328104]  [<c107b866>] ? fsnotify_access+0x5a/0x61
> [   60.328104]  [<c110097d>] ? ckpt_read_obj_type+0x16/0x70
> [   60.328104]  [<c1039ab8>] ? restore_ns+0x18/0x12b
> [   60.328104]  [<c10feb48>] ? restore_obj+0x98/0x116
> [   60.328104]  [<c11007ed>] ? ckpt_read_obj_dispatch+0x220/0x246
> [   60.328104]  [<c1100829>] ? ckpt_read_obj+0x16/0xe8
> [   60.328104]  [<c110097d>] ? ckpt_read_obj_type+0x16/0x70
> [   60.328104]  [<c11033fb>] ? restore_task+0x512/0x9fc
> [   60.328104]  [<c1101b59>] ? do_restart+0xff4/0x12f3
> [   60.328104]  [<c10364f0>] ? autoremove_wake_function+0x0/0x2d
> [   60.328104]  [<c10fdb21>] ? do_sys_restart+0x66/0x77
> [   60.328104]  [<c10027d5>] ? ptregs_restart+0x15/0x1c
> [   60.328104]  [<c10026d0>] ? sysenter_do_call+0x12/0x26
> [   60.328104] Code: fe ff ff e9 c8 01 00 00 8b 04 24 83 c0 64 89 44 24 10 e8 dd 16 10 00 8b 57 10 8b 04 24 83 c0 
> 74 e8 24 71 02 00 85 c0 89 c3 75 04 <0f> 0b eb fe 8b 68 2c 8d 45 18 3e ff 45 18 8b 44 24 04 8d 57 08
> [   60.328104] EIP: [<c10e0abe>] restore_ipc_shm+0x1a0/0x35a SS:ESP 0068:c7991dbc
> [   60.351332] ---[ end trace 9660dfa05be59307 ]---
> 
> 
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