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