Usually when kernel reach an oops condition, it's a point of no return;
in case not enough debug information is available in the kernel splat,
one of the last resorts would be to collect a kernel crash dump and
analyze it. The problem with this approach is that in order to collect
the dump, a panic is required (to kexec-load the crash kernel). When
in an environment of multiple virtual machines, users may prefer to
try living with the oops, at least until being able to properly
shutdown their VMs / finish their important tasks.

This patch implements a way to collect a bit more debug details when an
oops event is reached, by printing all the CPUs backtraces through the
usage of NMIs (on architectures that support that). The sysctl added
(and documented) here was called "oops_all_cpu_backtrace", and when
set will (as the name suggests) dump all CPUs backtraces.

Far from ideal, this may be the last option though for users that for
some reason cannot panic on oops. Most of times oopses are clear enough
to indicate the kernel portion that must be investigated, but in virtual
environments it's possible to observe hypervisor/KVM issues that could
lead to oopses shown in other guests CPUs (like virtual APIC crashes).
This patch hence aims to help debug such complex issues without
resorting to kdump.

...

--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h

@@ -513,6 +513,12 @@ static inline u32 int_sqrt64(u64 x)
 }
 #endif
 
+#ifdef CONFIG_SMP
+extern unsigned int sysctl_oops_all_cpu_backtrace;
+#else
+#define sysctl_oops_all_cpu_backtrace 0
+#endif /* CONFIG_SMP */
+