On 10/22/2014 12:27 AM, Rusty Russell wrote: > Prarit Bhargava <prarit at 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 at lwn.net> >> Cc: Andrew Morton <akpm at linux-foundation.org> >> Cc: Rusty Russell <rusty at rustcorp.com.au> >> Cc: "H. Peter Anvin" <hpa at zytor.com> >> Cc: Andi Kleen <ak at linux.intel.com> >> Cc: Masami Hiramatsu <masami.hiramatsu.pt at hitachi.com> >> Cc: Fabian Frederick <fabf at skynet.be> >> Cc: vgoyal at redhat.com >> Cc: isimatu.yasuaki at jp.fujitsu.com >> Cc: linux-doc at vger.kernel.org >> Cc: kexec at lists.infradead.org >> Cc: linux-api at vger.kernel.org >> Signed-off-by: Prarit Bhargava <prarit at 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.
