(2014/10/24 21:53), Prarit Bhargava 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 and > /proc/sys/kernel/bug_on_warn 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 > [v3]: use proc_dointvec_minmax() in sysctl handler > [v4]: remove !slowpath cases, and add __read_mostly > --- Looks good to me. Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki at jp.fujitsu.com> Thanks, Yasuaki Ishimatsu > Documentation/kdump/kdump.txt | 7 +++++++ > Documentation/kernel-parameters.txt | 3 +++ > Documentation/sysctl/kernel.txt | 12 ++++++++++++ > include/linux/kernel.h | 1 + > include/uapi/linux/sysctl.h | 1 + > kernel/panic.c | 21 ++++++++++++++++++++- > kernel/sysctl.c | 9 +++++++++ > kernel/sysctl_binary.c | 1 + > 8 files changed, 54 insertions(+), 1 deletion(-) > > 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. > > Contact > ======= > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt > index 74339c5..aa1d319 100644 > --- a/Documentation/kernel-parameters.txt > +++ b/Documentation/kernel-parameters.txt > @@ -553,6 +553,9 @@ 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(). Useful to cause kdump > + on a WARN(). > + > bulk_remove=off [PPC] This parameter disables the use of the pSeries > firmware feature for flushing multiple hpte entries > at a time. > diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt > index 57baff5..dcadcdc 100644 > --- a/Documentation/sysctl/kernel.txt > +++ b/Documentation/sysctl/kernel.txt > @@ -23,6 +23,7 @@ show up in /proc/sys/kernel: > - auto_msgmni > - bootloader_type [ X86 only ] > - bootloader_version [ X86 only ] > +- bug_on_warn > - callhome [ S390 only ] > - cap_last_cap > - core_pattern > @@ -152,6 +153,17 @@ Documentation/x86/boot.txt for additional information. > > ============================================================== > > +bug_on_warn: > + > +Calls BUG() in the WARN() path when set to 1. This is useful to avoid > +a kernel rebuild when attempting to kdump at the location of a WARN(). > + > +0: only WARN(), default behaviour. > + > +1: call BUG() after printing out WARN() location. > + > +============================================================== > + > callhome: > > Controls the kernel's callhome behavior in case of a kernel panic. > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 3d770f55..fc28bff 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -423,6 +423,7 @@ extern int panic_on_oops; > extern int panic_on_unrecovered_nmi; > extern int panic_on_io_nmi; > extern int sysctl_panic_on_stackoverflow; > +extern int bug_on_warn; > /* > * Only to be used by arch init code. If the user over-wrote the default > * CONFIG_PANIC_TIMEOUT, honor it. > diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h > index 43aaba1..2ba0a58 100644 > --- a/include/uapi/linux/sysctl.h > +++ b/include/uapi/linux/sysctl.h > @@ -153,6 +153,7 @@ enum > KERN_MAX_LOCK_DEPTH=74, /* int: rtmutex's maximum lock depth */ > KERN_NMI_WATCHDOG=75, /* int: enable/disable nmi watchdog */ > KERN_PANIC_ON_NMI=76, /* int: whether we will panic on an unrecovered */ > + KERN_BUG_ON_WARN=77, /* int: call BUG() in WARN() functions */ > }; > > > diff --git a/kernel/panic.c b/kernel/panic.c > index d09dc5c..740d9ff 100644 > --- a/kernel/panic.c > +++ b/kernel/panic.c > @@ -33,6 +33,7 @@ static int pause_on_oops; > static int pause_on_oops_flag; > static DEFINE_SPINLOCK(pause_on_oops_lock); > static bool crash_kexec_post_notifiers; > +int bug_on_warn __read_mostly; > > int panic_timeout = CONFIG_PANIC_TIMEOUT; > EXPORT_SYMBOL_GPL(panic_timeout); > @@ -420,13 +421,24 @@ static void warn_slowpath_common(const char *file, int line, void *caller, > { > disable_trace_on_warning(); > > - pr_warn("------------[ cut here ]------------\n"); > + if (!bug_on_warn) > + pr_warn("------------[ cut here ]------------\n"); > pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS()\n", > raw_smp_processor_id(), current->pid, file, line, caller); > > if (args) > vprintk(args->fmt, args->args); > > + if (bug_on_warn) { > + pr_warn("bug_on_warn set, calling BUG()...\n"); > + /* > + * A flood of WARN()s may occur. Prevent further WARN()s > + * from panicking the system. > + */ > + bug_on_warn = 0; > + BUG(); > + } > + > print_modules(); > dump_stack(); > print_oops_end_marker(); > @@ -501,3 +513,10 @@ static int __init oops_setup(char *s) > return 0; > } > early_param("oops", oops_setup); > + > +static int __init bug_on_warn_setup(char *s) > +{ > + bug_on_warn = 1; > + return 0; > +} > +early_param("bug_on_warn", bug_on_warn_setup); > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 4aada6d..818cd31 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1103,6 +1103,15 @@ static struct ctl_table kern_table[] = { > .proc_handler = proc_dointvec, > }, > #endif > + { > + .procname = "bug_on_warn", > + .data = &bug_on_warn, > + .maxlen = sizeof(int), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = &zero, > + .extra2 = &one, > + }, > { } > }; > > diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c > index 9a4f750..28376bf 100644 > --- a/kernel/sysctl_binary.c > +++ b/kernel/sysctl_binary.c > @@ -137,6 +137,7 @@ static const struct bin_table bin_kern_table[] = { > { CTL_INT, KERN_COMPAT_LOG, "compat-log" }, > { CTL_INT, KERN_MAX_LOCK_DEPTH, "max_lock_depth" }, > { CTL_INT, KERN_PANIC_ON_NMI, "panic_on_unrecovered_nmi" }, > + { CTL_INT, KERN_BUG_ON_WARN, "bug_on_warn" }, > {} > }; > >
