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SubjectRe: [PATCH V2] kernel, add bug_on_warn


On 10/22/2014 12:27 AM, Rusty Russell wrote:
> Prarit Bhargava <prarit@redhat.com> writes:
>> 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.
>>
>> An example of the bug_on_warn output:
>>
>> The first line below is from the WARN_ON() to output the WARN_ON()'s location.
>> After that the new BUG() call is displayed.
>>
>> 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 ]---
>>
>> Successfully tested by me.
>>
>> Cc: Jonathan Corbet <corbet@lwn.net>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Rusty Russell <rusty@rustcorp.com.au>
>> Cc: "H. Peter Anvin" <hpa@zytor.com>
>> Cc: Andi Kleen <ak@linux.intel.com>
>> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>> Cc: Fabian Frederick <fabf@skynet.be>
>> Cc: vgoyal@redhat.com
>> Cc: isimatu.yasuaki@jp.fujitsu.com
>> Cc: linux-doc@vger.kernel.org
>> Cc: kexec@lists.infradead.org
>> Cc: linux-api@vger.kernel.org
>> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
>>
>> [v2]: add /proc/sys/kernel/bug_on_warn, additional documentation, modify
>> !slowpath cases
>> ---
>> Documentation/kdump/kdump.txt | 7 +++++++
>> Documentation/kernel-parameters.txt | 3 +++
>> Documentation/sysctl/kernel.txt | 12 ++++++++++++
>> include/asm-generic/bug.h | 12 ++++++++++--
>> include/linux/kernel.h | 1 +
>> include/uapi/linux/sysctl.h | 1 +
>> kernel/panic.c | 21 ++++++++++++++++++++-
>> kernel/sysctl.c | 7 +++++++
>> kernel/sysctl_binary.c | 1 +
>> 9 files changed, 62 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
>> index 6c0b9f2..a04ed72 100644
>> --- a/Documentation/kdump/kdump.txt
>> +++ b/Documentation/kdump/kdump.txt
>> @@ -471,6 +471,13 @@ format. Crash is available on Dave Anderson's site at the following URL:
>>
>> http://people.redhat.com/~anderson/
>>
>> +Trigger Kdump on WARN()
>> +=======================
>> +
>> +The kernel parameter, bug_on_warn, calls BUG() in all WARN() paths. This
>> +will cause a kdump to occur at the BUG() call. In cases where a user
>> +wants to specify this during runtime, /proc/sys/kernel/bug_on_warn can be
>> +set to 1 to achieve the same behaviour.
>
> What about during early boot?

Hi Rusty,

I really don't have a use case for this in early boot. The kernel boots, the
initramfs, and then we run whatever init (systemd in my case). A systemd script
configures kexec for kdump and that point kdump is "armed". Doing a bug_on_warn
before this will simply result in a panicked system. I don't get any "new"
information FWIW as I get a stack trace, etc., in both the WARN() and BUG() cases.

>
> I'd recommend you use core_param(). Less code, and can be set on
> commandline.

Is that a general request, or is it dependent on the answer above? Of course I
have no problem doing it either way.

P.


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