linux-kernel - Re: [PATCH] kernel, add bug_on

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Message-ID: <5445E7D4.1090503@jp.fujitsu.com>
Date:	Tue, 21 Oct 2014 13:57:56 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Prarit Bhargava <prarit@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	<linux-kernel@...r.kernel.org>, Jonathan Corbet <corbet@....net>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Vivek Goyal <vgoyal@...hat.com>, <linux-doc@...r.kernel.org>
Subject: Re: [PATCH] kernel, add bug_on_warn

Hi Prarit,

(2014/10/21 9:54), Prarit Bhargava wrote:
>
>
> On 10/20/2014 06:24 PM, Andrew Morton wrote:
>> On Mon, 20 Oct 2014 08:00:20 -0400 Prarit Bhargava <prarit@...hat.com> wrote:
>>
>>> There have been several times where I have had to rebuild a kernel to
>>> cause a panic when hitting a WARN() in the code in order to get a crash
>>> dump from a system.  Sometimes this is easy to do, other times (such as
>>> in the case of a remote admin) it is not trivial to send new images to the
>>> user.
>>>
>>> A much easier method would be a switch to change the WARN() over to a
>>> BUG().  This makes debugging easier in that I can now test the actual
>>> image the WARN() was seen on and I do not have to engage in remote
>>> debugging.
>>>
>>> This patch adds a bug_on_warn kernel parameter, which calls BUG() in the
>>> warn_slowpath_common() path.  The function will still print out the
>>> location of the warning.
>>>
>>> Successfully tested by me.
>>
>> Looks nice and simple and useful.  However I suspect you're exclusively
>> focussed on "I want a crash dump" and things haven't been fully thought
>> through.
>>
>> - Do you have any example WARN->BUG console output at hand?  I'd like
>>    to check for missing or duplicated info.
>
> Yep, here you go, with some additional annotation notes from me.  The first
> line below is from the WARN_ON() to output the WARN_ON()'s location.  After
> that, we hit the new BUG() call.
>
>   WARNING: CPU: 27 PID: 3204 at
> /home/rhel7/redhat/debug/dummy-module/dummy-module.c:25 init_dummy+0x28/0x30
> [dummy_module]()
>   bug_on_warn set, calling BUG()...
>   ------------[ cut here ]------------
>   kernel BUG at kernel/panic.c:434!
>   invalid opcode: 0000 [#1] SMP
>   Modules linked in: dummy_module(OE+) sg nfsv3 rpcsec_gss_krb5 nfsv4
> dns_resolver nfs fscache cfg80211 rfkill x86_pkg_temp_thermal intel_powerclamp
> coretemp kvm_intel kvm crct10dif_pclmul crc32_pclmul crc32c_intel
> ghash_clmulni_intel igb iTCO_wdt aesni_intel iTCO_vendor_support lrw gf128mul
> sb_edac ptp edac_core glue_helper lpc_ich ioatdma pcspkr ablk_helper pps_core
> i2c_i801 mfd_core cryptd dca shpchp ipmi_si wmi ipmi_msghandler acpi_cpufreq
> nfsd auth_rpcgss nfs_acl lockd grace sunrpc xfs libcrc32c sr_mod cdrom sd_mod
> mgag200 syscopyarea sysfillrect sysimgblt i2c_algo_bit drm_kms_helper isci ttm
> drm libsas ahci libahci scsi_transport_sas libata i2c_core dm_mirror
> dm_region_hash dm_log dm_mod
>   CPU: 27 PID: 3204 Comm: insmod Tainted: G           OE  3.17.0+ #19
>   Hardware name: Intel Corporation S2600CP/S2600CP, BIOS
> RMLSDP.86I.00.29.D696.1311111329 11/11/2013
>   task: ffff880034e75160 ti: ffff8807fc5ac000 task.ti: ffff8807fc5ac000
>   RIP: 0010:[<ffffffff81076b81>]  [<ffffffff81076b81>] warn_slowpath_common+0xc1/0xd0
>   RSP: 0018:ffff8807fc5afc68  EFLAGS: 00010246
>   RAX: 0000000000000021 RBX: ffff8807fc5afcb0 RCX: 0000000000000000
>   RDX: 0000000000000000 RSI: ffff88081efee5f8 RDI: ffff88081efee5f8
>   RBP: ffff8807fc5afc98 R08: 0000000000000096 R09: 0000000000000000
>   R10: 0000000000000711 R11: ffff8807fc5af93e R12: ffffffffa0424070
>   R13: 0000000000000019 R14: ffffffffa0423068 R15: 0000000000000009
>   FS:  00007f2d4b034740(0000) GS:ffff88081efe0000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 00007f2d4a99f3c0 CR3: 00000007fd88b000 CR4: 00000000001407e0
>   Stack:
>    ffff8807fc5afcb8 ffffffff8199f020 ffff88080e396160 0000000000000000
>    ffffffffa0423040 ffffffffa0425000 ffff8807fc5afd08 ffffffff81076be5
>    0000000000000008 ffffffffa0424053 ffff880700000018 ffff8807fc5afd18
>   Call Trace:
>    [<ffffffffa0423040>] ? dummy_greetings+0x40/0x40 [dummy_module]
>    [<ffffffff81076be5>] warn_slowpath_fmt+0x55/0x70
>    [<ffffffffa0423068>] init_dummy+0x28/0x30 [dummy_module]
>    [<ffffffff81002144>] do_one_initcall+0xd4/0x210
>    [<ffffffff811b52c2>] ? __vunmap+0xc2/0x110
>    [<ffffffff810f8889>] load_module+0x16a9/0x1b30
>    [<ffffffff810f3d30>] ? store_uevent+0x70/0x70
>    [<ffffffff810f49b9>] ? copy_module_from_fd.isra.44+0x129/0x180
>    [<ffffffff810f8ec6>] SyS_finit_module+0xa6/0xd0
>    [<ffffffff8166ce29>] system_call_fastpath+0x12/0x17
>   Code: c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d c3 48 c7 c7 20 42 8a 81 31 c0 e8 fc
> 80 5e 00 eb 80 48 c7 c7 78 42 8a 81 31 c0 e8 ec 80 5e 00 <0f> 0b 66 66 66 66 2e
> 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55
>   RIP  [<ffffffff81076b81>] warn_slowpath_common+0xc1/0xd0
>    RSP <ffff8807fc5afc68>
>   ---[ end trace 428218934a12088b ]---
>>
>> - Did you consider permitting this to be tweaked at runtime via
>>    /proc?  Sometimes we get pesky WARNs at boot time and having runtime
>>    alteration would permit the user to prevent those from tripping a
>>    BUG.
>>
>
> I did actually, but I was wondering how people liked the idea before I looked
> at the /proc implementation.  It's pretty much the same as panic_on_oops, so
> it's not difficult to do.
>
>> - Also, perhaps bug_on_warn should be single-shot: clear itself after
>>    it has triggered one BUG.  Because once the kernel has gone
>>    WARN->BUG, it's probably messed up and is likely to trigger more
>>    WARNs.  Also, the kernel might generate many WARNs for the same
>>    issue.
>
> Okay, I'll add that.

When you update it, please CC me.
Your patch works well as follows:


  WARNING: CPU: 3 PID: 468 at mm/page_alloc.c:4968 free_area_init_node+0x3fe/0x426()
  bug_on_warn set, calling BUG()...
  ------------[ cut here ]------------
  kernel BUG at kernel/panic.c:434!
  invalid opcode: 0000 [#1] SMP
  <...>
  Workqueue: kacpi_hotplug acpi_hotplug_work_fn
  task: ffff880866d8c3d0 ti: ffff88086227c000 task.ti: ffff88086227c000
  RIP: 0010:[<ffffffff81074001>]  [<ffffffff81074001>] warn_slowpath_common+0xc1/0xd0
  RSP: 0018:ffff88086227fa68  EFLAGS: 00010246
  RAX: 0000000000000021 RBX: 0000000000000000 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: ffff88087fa6e5f8 RDI: ffff88087fa6e5f8
  RBP: ffff88086227fa98 R08: 0000000000000096 R09: 0000000000000000
  R10: 0000000000000b37 R11: ffff88086227f73e R12: ffffffff818a9195
  R13: 0000000000001368 R14: ffffffff81651b17 R15: 0000000000000009
  FS:  0000000000000000(0000) GS:ffff88087fa60000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f8301965000 CR3: 0000000001984000 CR4: 00000000001407e0
  Stack:
   ffff88086f00e5e8 0000000000000002 ffff8a07fffb4000 0000000040000000
   0000000000000002 0000000000000002 ffff88086227faa8 ffffffff8107410a
   ffff88086227fb38 ffffffff81651b17 0000000000000296 ffff88087f402120
  Call Trace:
   [<ffffffff8107410a>] warn_slowpath_null+0x1a/0x20
   [<ffffffff81651b17>] free_area_init_node+0x3fe/0x426
   [<ffffffff810b9d22>] ? up+0x32/0x50
   [<ffffffff8164ddd0>] hotadd_new_pgdat+0x90/0x110
   [<ffffffff8164df24>] add_memory+0xd4/0x200
   [<ffffffff813a8329>] acpi_memory_device_add+0x1aa/0x289
   [<ffffffff8137b486>] acpi_bus_attach+0xfd/0x204
   [<ffffffff8140fd1e>] ? device_register+0x1e/0x30
   [<ffffffff8137b501>] acpi_bus_attach+0x178/0x204
   [<ffffffff8137b5f7>] acpi_bus_scan+0x6a/0x90
   [<ffffffff813786d2>] ? acpi_bus_get_status+0x2d/0x5f
   [<ffffffff8137b7a7>] acpi_device_hotplug+0xe8/0x418
   [<ffffffff813750d9>] acpi_hotplug_work_fn+0x1f/0x2b
   [<ffffffff8108cc5e>] process_one_work+0x14e/0x3f0
   [<ffffffff8108d36b>] worker_thread+0x11b/0x510
   [<ffffffff8108d250>] ? rescuer_thread+0x350/0x350
   [<ffffffff81092af1>] kthread+0xe1/0x100
   [<ffffffff81092a10>] ? kthread_create_on_node+0x1b0/0x1b0
   [<ffffffff81663efc>] ret_from_fork+0x7c/0xb0
   [<ffffffff81092a10>] ? kthread_create_on_node+0x1b0/0x1b0
  Code: c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d c3 48 c7 c7 60 20 89 81 31 c0 e8 5c 26 5e 00 eb 80 48 c7 c7 b8 20 89 81 31 c0 e8 4c 26 5e 00 <0f> 0b 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55
  RIP  [<ffffffff81074001>] warn_slowpath_common+0xc1/0xd0
   RSP <ffff88086227fa68>

Thanks,
Yasuaki Ishimatsu

>
>>
>>> --- a/Documentation/kernel-parameters.txt
>>> +++ b/Documentation/kernel-parameters.txt
>>> @@ -553,6 +553,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>>   	bttv.pll=	See Documentation/video4linux/bttv/Insmod-options
>>>   	bttv.tuner=
>>>
>>> +	bug_on_warn	BUG() instead of WARN()
>>
>> There's no mention here that this feature is mainly aimed at generating
>> a crash dump.  How do we tell the people who aren't reading this email
>> thread (ie: all of humanity except you and me ;)) that this feature
>> even exists?  Is there crash dump documentation that we can update?
>>
>
> I'll look into this too.
>
> P.
>>
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