[RFC v3] debug: prevent entering debug mode on errors

[Kiran Raparthy]

From: Colin Cross <ccross@xxxxxxxxxxx>

debug: prevent entering debug mode on errors

On non-developer devices kgdb prevents CONFIG_PANIC_TIMEOUT from rebooting the
device after a panic.

In case of panics and exceptions, to honor CONFIG_PANIC_TIMEOUT, prevent
entering debug mode to avoid getting stuck waiting for the user to interact
with debugger.

Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
Cc: kgdb-bugreport@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Android Kernel Team <kernel-team@xxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx>
[Kiran: Added context to commit message.
panic_timeout is used instead of break_on_panic and
break_on_exception to honor CONFIG_PANIC_TIMEOUT]
Signed-off-by: Kiran Raparthy <kiran.kumar@xxxxxxxxxx>
---
 kernel/debug/debug_core.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 1adf62b..0012a1f 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -689,6 +689,14 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 
 	if (arch_kgdb_ops.enable_nmi)
 		arch_kgdb_ops.enable_nmi(0);
+	/*
+	 * Avoid entering the debugger if we were triggered due to an oops
+	 * but panic_timeout indicates the system should automatically
+	 * reboot on panic. We don't want to get stuck waiting for input
+	 * on such systems, especially if its "just" an oops.
+	 */
+	if (signo != SIGTRAP && panic_timeout)
+		return 1;
 
 	memset(ks, 0, sizeof(struct kgdb_state));
 	ks->cpu			= raw_smp_processor_id();
@@ -821,6 +829,15 @@ static int kgdb_panic_event(struct notifier_block *self,
 			    unsigned long val,
 			    void *data)
 {
+	/*
+	 * Avoid entering the debugger if we were triggered due to a panic
+	 * We don't want to get stuck waiting for input from user in such case.
+	 * panic_timeout indicates the system should automatically
+	 * reboot on panic.
+	 */
+	if (panic_timeout)
+		return NOTIFY_DONE;
+
 	if (dbg_kdb_mode)
 		kdb_printf("PANIC: %s\n", (char *)data);
 	kgdb_breakpoint();
-- 
1.8.2.1

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