path: root/kernel/panic.c
diff options
authorGuilherme G. Piccoli <gpiccoli@canonical.com>2020-06-07 21:40:48 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-08 11:05:56 -0700
commit60c958d8df9cfc40b745d6cd583cfbfa7525ead6 (patch)
treee5a4b6250bf68de91fb7d610be942fe6219167a0 /kernel/panic.c
parent0ec9dc9bcba0a62b0844e54c1caf6b8b0bf6b5b4 (diff)
panic: add sysctl to dump all CPUs backtraces on oops event
Usually when the kernel reaches 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. Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Iurii Zaikin <yzaikin@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Matthew Wilcox <willy@infradead.org> Link: http://lkml.kernel.org/r/20200327224116.21030-1-gpiccoli@canonical.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/panic.c')
1 files changed, 11 insertions, 0 deletions
diff --git a/kernel/panic.c b/kernel/panic.c
index 94b5c973770c..85568bbfb12b 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -36,6 +36,14 @@
#define PANIC_TIMER_STEP 100
#define PANIC_BLINK_SPD 18
+#ifdef CONFIG_SMP
+ * Should we dump all CPUs backtraces in an oops event?
+ * Defaults to 0, can be changed via sysctl.
+ */
+unsigned int __read_mostly sysctl_oops_all_cpu_backtrace;
+#endif /* CONFIG_SMP */
int panic_on_oops = CONFIG_PANIC_ON_OOPS_VALUE;
static unsigned long tainted_mask =
@@ -522,6 +530,9 @@ void oops_enter(void)
/* can't trust the integrity of the kernel anymore: */
+ if (sysctl_oops_all_cpu_backtrace)
+ trigger_all_cpu_backtrace();

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