[PATCH] sysctl: Add panic-fatal-signals

[Vincent Whitchurch]

Add a sysctl which asks the kernel to panic when any userspace process
receives a fatal signal which would trigger a core dump.  This has
proven to be quite useful when debugging problems seen during testing of
embedded systems:  When combined with kernel core dumps (saved due to
the panic), it allows easier debugging of crashes which have their
origin in system-wide problems such as buggy drivers or other kernel or
hardware-related issues.

The crashing process's core dump can be extracted from the kernel core
dump using tools such as the crash utility's gcore extension.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
---
 include/linux/signal.h | 1 +
 kernel/signal.c        | 5 ++++-
 kernel/sysctl.c        | 7 +++++++
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index cc7e2c1cd444..109efd1432e9 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -10,6 +10,7 @@ struct task_struct;
 
 /* for sysctl */
 extern int print_fatal_signals;
+extern int panic_fatal_signals;
 
 static inline void copy_siginfo(kernel_siginfo_t *to,
 				const kernel_siginfo_t *from)
diff --git a/kernel/signal.c b/kernel/signal.c
index e1d7ad8e6ab1..83c6877b0182 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -59,6 +59,7 @@
 static struct kmem_cache *sigqueue_cachep;
 
 int print_fatal_signals __read_mostly;
+int panic_fatal_signals __read_mostly;
 
 static void __user *sig_handler(struct task_struct *t, int sig)
 {
@@ -2497,8 +2498,10 @@ bool get_signal(struct ksignal *ksig)
 		current->flags |= PF_SIGNALED;
 
 		if (sig_kernel_coredump(signr)) {
-			if (print_fatal_signals)
+			if (print_fatal_signals || panic_fatal_signals)
 				print_fatal_signal(ksig->info.si_signo);
+			if (panic_fatal_signals)
+				panic("Fatal signal and panic_fatal_signals=1");
 			proc_coredump_connector(current);
 			/*
 			 * If it was able to dump core, this kills all
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ba4d9e85feb8..ad1ac6ec2004 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -557,6 +557,13 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "panic-fatal-signals",
+		.data		= &panic_fatal_signals,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 #ifdef CONFIG_SPARC
 	{
 		.procname	= "reboot-cmd",
-- 
2.20.0