mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-16 09:13:55 +08:00
8ae34ea7e8
s/BOOTPARAM_HARDLOCKUP_PANIC/BOOTPARAM_SOFTLOCKUP_PANIC Signed-off-by: Harish Jenny K N <harish_kandiga@mentor.com> Acked-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
64 lines
3.1 KiB
Plaintext
64 lines
3.1 KiB
Plaintext
===============================================================
|
|
Softlockup detector and hardlockup detector (aka nmi_watchdog)
|
|
===============================================================
|
|
|
|
The Linux kernel can act as a watchdog to detect both soft and hard
|
|
lockups.
|
|
|
|
A 'softlockup' is defined as a bug that causes the kernel to loop in
|
|
kernel mode for more than 20 seconds (see "Implementation" below for
|
|
details), without giving other tasks a chance to run. The current
|
|
stack trace is displayed upon detection and, by default, the system
|
|
will stay locked up. Alternatively, the kernel can be configured to
|
|
panic; a sysctl, "kernel.softlockup_panic", a kernel parameter,
|
|
"softlockup_panic" (see "Documentation/kernel-parameters.txt" for
|
|
details), and a compile option, "BOOTPARAM_SOFTLOCKUP_PANIC", are
|
|
provided for this.
|
|
|
|
A 'hardlockup' is defined as a bug that causes the CPU to loop in
|
|
kernel mode for more than 10 seconds (see "Implementation" below for
|
|
details), without letting other interrupts have a chance to run.
|
|
Similarly to the softlockup case, the current stack trace is displayed
|
|
upon detection and the system will stay locked up unless the default
|
|
behavior is changed, which can be done through a compile time knob,
|
|
"BOOTPARAM_HARDLOCKUP_PANIC", and a kernel parameter, "nmi_watchdog"
|
|
(see "Documentation/kernel-parameters.txt" for details).
|
|
|
|
The panic option can be used in combination with panic_timeout (this
|
|
timeout is set through the confusingly named "kernel.panic" sysctl),
|
|
to cause the system to reboot automatically after a specified amount
|
|
of time.
|
|
|
|
=== Implementation ===
|
|
|
|
The soft and hard lockup detectors are built on top of the hrtimer and
|
|
perf subsystems, respectively. A direct consequence of this is that,
|
|
in principle, they should work in any architecture where these
|
|
subsystems are present.
|
|
|
|
A periodic hrtimer runs to generate interrupts and kick the watchdog
|
|
task. An NMI perf event is generated every "watchdog_thresh"
|
|
(compile-time initialized to 10 and configurable through sysctl of the
|
|
same name) seconds to check for hardlockups. If any CPU in the system
|
|
does not receive any hrtimer interrupt during that time the
|
|
'hardlockup detector' (the handler for the NMI perf event) will
|
|
generate a kernel warning or call panic, depending on the
|
|
configuration.
|
|
|
|
The watchdog task is a high priority kernel thread that updates a
|
|
timestamp every time it is scheduled. If that timestamp is not updated
|
|
for 2*watchdog_thresh seconds (the softlockup threshold) the
|
|
'softlockup detector' (coded inside the hrtimer callback function)
|
|
will dump useful debug information to the system log, after which it
|
|
will call panic if it was instructed to do so or resume execution of
|
|
other kernel code.
|
|
|
|
The period of the hrtimer is 2*watchdog_thresh/5, which means it has
|
|
two or three chances to generate an interrupt before the hardlockup
|
|
detector kicks in.
|
|
|
|
As explained above, a kernel knob is provided that allows
|
|
administrators to configure the period of the hrtimer and the perf
|
|
event. The right value for a particular environment is a trade-off
|
|
between fast response to lockups and detection overhead.
|