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Message-ID: <544EDC80.9060402@jp.fujitsu.com>
Date: Tue, 28 Oct 2014 09:00:00 +0900
From: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To: Prarit Bhargava <prarit@...hat.com>
CC: <linux-kernel@...r.kernel.org>, Jonathan Corbet <corbet@....net>,
Andrew Morton <akpm@...ux-foundation.org>,
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>,
Fabian Frederick <fabf@...net.be>, <vgoyal@...hat.com>,
<linux-doc@...r.kernel.org>, <kexec@...ts.infradead.org>,
<linux-api@...r.kernel.org>
Subject: Re: [PATCH V4] kernel, add bug_on_warn
(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@....net>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Fabian Frederick <fabf@...net.be>
> Cc: vgoyal@...hat.com
> Cc: isimatu.yasuaki@...fujitsu.com
> Cc: linux-doc@...r.kernel.org
> Cc: kexec@...ts.infradead.org
> Cc: linux-api@...r.kernel.org
> Signed-off-by: Prarit Bhargava <prarit@...hat.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@...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" },
> {}
> };
>
>
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