path: root/Documentation
diff options
authorAaron Tomlin <atomlin@redhat.com>2014-06-23 13:22:05 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-23 16:47:44 -0700
commited235875e2ca983197831337a986f0517074e1a0 (patch)
treea562c7ac13452a0573b87977df7b26a6471ece38 /Documentation
parentf3aca3d09525f87731ba6b892c9b010570bc54b4 (diff)
kernel/watchdog.c: print traces for all cpus on lockup detection
A 'softlockup' is defined as a bug that causes the kernel to loop in kernel mode for more than a predefined period to time, without giving other tasks a chance to run. Currently, upon detection of this condition by the per-cpu watchdog task, debug information (including a stack trace) is sent to the system log. On some occasions, we have observed that the "victim" rather than the actual "culprit" (i.e. the owner/holder of the contended resource) is reported to the user. Often this information has proven to be insufficient to assist debugging efforts. To avoid loss of useful debug information, for architectures which support NMI, this patch makes it possible to improve soft lockup reporting. This is accomplished by issuing an NMI to each cpu to obtain a stack trace. If NMI is not supported we just revert back to the old method. A sysctl and boot-time parameter is available to toggle this feature. [dzickus@redhat.com: add CONFIG_SMP in certain areas] [akpm@linux-foundation.org: additional CONFIG_SMP=n optimisations] [mq@suse.cz: fix warning] Signed-off-by: Aaron Tomlin <atomlin@redhat.com> Signed-off-by: Don Zickus <dzickus@redhat.com> Cc: David S. Miller <davem@davemloft.net> Cc: Mateusz Guzik <mguzik@redhat.com> Cc: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Jan Moskyto Matejka <mq@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
2 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 884904975d0b..c1b9aa8c5a52 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3130,6 +3130,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
[KNL] Should the soft-lockup detector generate panics.
Format: <integer>
+ softlockup_all_cpu_backtrace=
+ [KNL] Should the soft-lockup detector generate
+ backtraces on all cpus.
+ Format: <integer>
sonypi.*= [HW] Sony Programmable I/O Control Device driver
See Documentation/laptops/sonypi.txt
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 708bb7f1b7e0..c14374e71775 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -75,6 +75,7 @@ show up in /proc/sys/kernel:
- shmall
- shmmax [ sysv ipc ]
- shmmni
+- softlockup_all_cpu_backtrace
- stop-a [ SPARC only ]
- sysrq ==> Documentation/sysrq.txt
- sysctl_writes_strict
@@ -783,6 +784,22 @@ via the /proc/sys interface:
+This value controls the soft lockup detector thread's behavior
+when a soft lockup condition is detected as to whether or not
+to gather further debug information. If enabled, each cpu will
+be issued an NMI and instructed to capture stack trace.
+This feature is only applicable for architectures which support
+0: do nothing. This is the default behavior.
+1: on detection capture more debug information.
Non-zero if the kernel has been tainted. Numeric values, which

Privacy Policy