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 <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Fabian Frederick <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Prarit Bhargava <[email protected]>
[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.
Contact
=======
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 988160a..3890a3a 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/asm-generic/bug.h b/include/asm-generic/bug.h
index 630dd23..4d0c763 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -75,10 +75,18 @@ extern void warn_slowpath_null(const char *file, const int line);
#define __WARN_printf_taint(taint, arg...) \
warn_slowpath_fmt_taint(__FILE__, __LINE__, taint, arg)
#else
-#define __WARN() __WARN_TAINT(TAINT_WARN)
+#define check_bug_on_warn() \
+ do { \
+ if (bug_on_warn) \
+ BUG(); \
+ } while (0)
+
+#define __WARN() \
+ do { __WARN_TAINT(TAINT_WARN); check_bug_on_warn(); } while (0)
+
#define __WARN_printf(arg...) do { printk(arg); __WARN(); } while (0)
#define __WARN_printf_taint(taint, arg...) \
- do { printk(arg); __WARN_TAINT(taint); } while (0)
+ do { printk(arg); __WARN_TAINT(taint); check_bug_on_warn(); } while (0)
#endif
#ifndef WARN_ON
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 40728cf..4094a60 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -422,6 +422,7 @@ 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..a6d2e2f 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;
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..030bb5d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1103,6 +1103,13 @@ 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,
+ },
{ }
};
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" },
{}
};
--
1.7.9.3
Prarit Bhargava <[email protected]> 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 <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Rusty Russell <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: Andi Kleen <[email protected]>
> Cc: Masami Hiramatsu <[email protected]>
> Cc: Fabian Frederick <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Prarit Bhargava <[email protected]>
>
> [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.
On 10/22/2014 12:27 AM, Rusty Russell wrote:
> Prarit Bhargava <[email protected]> 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 <[email protected]>
>> Cc: Andrew Morton <[email protected]>
>> Cc: Rusty Russell <[email protected]>
>> Cc: "H. Peter Anvin" <[email protected]>
>> Cc: Andi Kleen <[email protected]>
>> Cc: Masami Hiramatsu <[email protected]>
>> Cc: Fabian Frederick <[email protected]>
>> Cc: [email protected]
>> Cc: [email protected]
>> Cc: [email protected]
>> Cc: [email protected]
>> Cc: [email protected]
>> Signed-off-by: Prarit Bhargava <[email protected]>
>>
>> [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.
(2014/10/22 1:47), 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, 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 <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Rusty Russell <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: Andi Kleen <[email protected]>
> Cc: Masami Hiramatsu <[email protected]>
> Cc: Fabian Frederick <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Prarit Bhargava <[email protected]>
>
> [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.
>
> Contact
> =======
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 988160a..3890a3a 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/asm-generic/bug.h b/include/asm-generic/bug.h
> index 630dd23..4d0c763 100644
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -75,10 +75,18 @@ extern void warn_slowpath_null(const char *file, const int line);
> #define __WARN_printf_taint(taint, arg...) \
> warn_slowpath_fmt_taint(__FILE__, __LINE__, taint, arg)
> #else
> -#define __WARN() __WARN_TAINT(TAINT_WARN)
> +#define check_bug_on_warn() \
> + do { \
> + if (bug_on_warn) \
> + BUG(); \
> + } while (0)
> +
> +#define __WARN() \
> + do { __WARN_TAINT(TAINT_WARN); check_bug_on_warn(); } while (0)
> +
> #define __WARN_printf(arg...) do { printk(arg); __WARN(); } while (0)
> #define __WARN_printf_taint(taint, arg...) \
> - do { printk(arg); __WARN_TAINT(taint); } while (0)
> + do { printk(arg); __WARN_TAINT(taint); check_bug_on_warn(); } while (0)
> #endif
>
> #ifndef WARN_ON
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 40728cf..4094a60 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -422,6 +422,7 @@ 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..a6d2e2f 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;
>
> 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..030bb5d 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1103,6 +1103,13 @@ 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,
How about use:
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
Document says as follows but it can set other vaule.
> +0: only WARN(), default behaviour.
> +
> +1: call BUG() after printing out WARN() location.
Thanks,
Yasuaki Ishimatsu
> + },
> { }
> };
>
> 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" },
> {}
> };
>
>
Prarit Bhargava <[email protected]> writes:
> On 10/22/2014 12:27 AM, Rusty Russell wrote:
>> Prarit Bhargava <[email protected]> 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.
>>
>> 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.
Oops, I read your initial patch too lightly: I see you added both
a sysctl (which I saw) and an early_param (which I didn't).
I still think it should be a core_param, like so (untested!):
diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 6c0b9f27e465..cf16cbe9f544 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, /sys/module/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 74339c57b914..aa1d3198e987 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/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 630dd2372238..4d0c763862b0 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -75,10 +75,18 @@ extern void warn_slowpath_null(const char *file, const int line);
#define __WARN_printf_taint(taint, arg...) \
warn_slowpath_fmt_taint(__FILE__, __LINE__, taint, arg)
#else
-#define __WARN() __WARN_TAINT(TAINT_WARN)
+#define check_bug_on_warn() \
+ do { \
+ if (bug_on_warn) \
+ BUG(); \
+ } while (0)
+
+#define __WARN() \
+ do { __WARN_TAINT(TAINT_WARN); check_bug_on_warn(); } while (0)
+
#define __WARN_printf(arg...) do { printk(arg); __WARN(); } while (0)
#define __WARN_printf_taint(taint, arg...) \
- do { printk(arg); __WARN_TAINT(taint); } while (0)
+ do { printk(arg); __WARN_TAINT(taint); check_bug_on_warn(); } while (0)
#endif
#ifndef WARN_ON
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3d770f5564b8..d583df09ee82 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 bool 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/kernel/panic.c b/kernel/panic.c
index d09dc5c32c67..3d345357fcc8 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;
+bool bug_on_warn;
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 = false;
+ BUG();
+ }
+
print_modules();
dump_stack();
print_oops_end_marker();
@@ -484,6 +496,7 @@ EXPORT_SYMBOL(__stack_chk_fail);
core_param(panic, panic_timeout, int, 0644);
core_param(pause_on_oops, pause_on_oops, int, 0644);
+core_param(bug_on_warn, bug_on_warn, bool, 0644);
static int __init setup_crash_kexec_post_notifiers(char *s)
{
On 10/30/2014 08:25 PM, Rusty Russell wrote:
> Prarit Bhargava <[email protected]> writes:
>> On 10/22/2014 12:27 AM, Rusty Russell wrote:
>>> Prarit Bhargava <[email protected]> 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.
>>>
>>> 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.
Yeah, I was just starting to do this and then I saw Hedi's comment about
disabling panic_on_warn during kdump to avoid a situation where the kdump kernel
bogus panics on a warn.
So that makes the setup function look like:
static int __init panic_on_warn_setup(char *s)
{
/* Enabling this on a kdump kernel could cause a bogus panic. */
if (!is_kdump_kernel())
panic_on_warn = 1;
return 0;
}
early_param("panic_on_warn", panic_on_warn_setup);
... so I dunno if core_param would work here :(. It would have been nice if it did.
P.