[PATCH 1/2] KGDB/KDB: add support for external NMI handler to call KGDB/KDB.

[Mike Travis]

This patch adds a kgdb_nmicallin() interface that can be used by
external NMI handlers to call the KGDB/KDB handler.  The primary need
for this is for those types of NMI interrupts where all the CPUs
have already received the NMI signal.  Therefore no send_IPI(NMI)
is required, and in fact it will cause a 2nd unhandled NMI to occur.
This generates the "Dazed and Confuzed" messages.

Since all the CPUs are getting the NMI at roughly the same time, it's not
guaranteed that the first CPU that hits the NMI handler will manage to
enter KGDB and set the dbg_master_lock before the slaves start entering.
The new argument "send_ready" was added for KGDB to signal the NMI handler
to release the slave CPUs for entry into KGDB.

Signed-off-by: Mike Travis <travis@xxxxxxx>
Reviewed-by: Dimitri Sivanich <sivanich@xxxxxxx>
Reviewed-by: Hedi Berriche <hedi@xxxxxxx>
Acked-by: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
---
v3: make entry into SYSTEM_NMI section more specific
---
 include/linux/kdb.h             |    1 +
 include/linux/kgdb.h            |    1 +
 kernel/debug/debug_core.c       |   30 +++++++++++++++++++++++++++++-
 kernel/debug/debug_core.h       |    1 +
 kernel/debug/kdb/kdb_debugger.c |    5 ++++-
 kernel/debug/kdb/kdb_main.c     |    3 +++
 6 files changed, 39 insertions(+), 2 deletions(-)

--- linux.orig/include/linux/kdb.h
+++ linux/include/linux/kdb.h
@@ -109,6 +109,7 @@ typedef enum {
 	KDB_REASON_RECURSE,	/* Recursive entry to kdb;
 				 * regs probably valid */
 	KDB_REASON_SSTEP,	/* Single Step trap. - regs valid */
+	KDB_REASON_SYSTEM_NMI,	/* In NMI due to SYSTEM cmd; regs valid */
 } kdb_reason_t;
 
 extern int kdb_trap_printk;
--- linux.orig/include/linux/kgdb.h
+++ linux/include/linux/kgdb.h
@@ -310,6 +310,7 @@ extern int
 kgdb_handle_exception(int ex_vector, int signo, int err_code,
 		      struct pt_regs *regs);
 extern int kgdb_nmicallback(int cpu, void *regs);
+extern int kgdb_nmicallin(int cpu, int trapnr, void *regs, atomic_t *snd_rdy);
 extern void gdbstub_exit(int status);
 
 extern int			kgdb_single_step;
--- linux.orig/kernel/debug/debug_core.c
+++ linux/kernel/debug/debug_core.c
@@ -575,8 +575,12 @@ return_normal:
 		raw_spin_lock(&dbg_slave_lock);
 
 #ifdef CONFIG_SMP
+	/* If SYSTEM_NMI, slaves are already waiting */
+	if (ks->err_code == KDB_REASON_SYSTEM_NMI)
+		atomic_set(ks->send_ready, 1);
+
 	/* Signal the other CPUs to enter kgdb_wait() */
-	if ((!kgdb_single_step) && kgdb_do_roundup)
+	else if ((!kgdb_single_step) && kgdb_do_roundup)
 		kgdb_roundup_cpus(flags);
 #endif
 
@@ -729,6 +733,30 @@ int kgdb_nmicallback(int cpu, void *regs
 		return 0;
 	}
 #endif
+	return 1;
+}
+
+int kgdb_nmicallin(int cpu, int trapnr, void *regs, atomic_t *send_ready)
+{
+#ifdef CONFIG_SMP
+	if (!kgdb_io_ready(0) || !send_ready)
+		return 1;
+
+	if (kgdb_info[cpu].enter_kgdb == 0) {
+		struct kgdb_state kgdb_var;
+		struct kgdb_state *ks = &kgdb_var;
+
+		memset(ks, 0, sizeof(struct kgdb_state));
+		ks->cpu			= cpu;
+		ks->ex_vector		= trapnr;
+		ks->signo		= SIGTRAP;
+		ks->err_code		= KDB_REASON_SYSTEM_NMI;
+		ks->linux_regs		= regs;
+		ks->send_ready		= send_ready;
+		kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
+		return 0;
+	}
+#endif
 	return 1;
 }
 
--- linux.orig/kernel/debug/debug_core.h
+++ linux/kernel/debug/debug_core.h
@@ -26,6 +26,7 @@ struct kgdb_state {
 	unsigned long		threadid;
 	long			kgdb_usethreadid;
 	struct pt_regs		*linux_regs;
+	atomic_t		*send_ready;
 };
 
 /* Exception state values */
--- linux.orig/kernel/debug/kdb/kdb_debugger.c
+++ linux/kernel/debug/kdb/kdb_debugger.c
@@ -69,7 +69,10 @@ int kdb_stub(struct kgdb_state *ks)
 	if (atomic_read(&kgdb_setting_breakpoint))
 		reason = KDB_REASON_KEYBOARD;
 
-	if (in_nmi())
+	if (ks->err_code == KDB_REASON_SYSTEM_NMI && ks->signo == SIGTRAP)
+		reason = KDB_REASON_SYSTEM_NMI;
+
+	else if (in_nmi())
 		reason = KDB_REASON_NMI;
 
 	for (i = 0, bp = kdb_breakpoints; i < KDB_MAXBPT; i++, bp++) {
--- linux.orig/kernel/debug/kdb/kdb_main.c
+++ linux/kernel/debug/kdb/kdb_main.c
@@ -1200,6 +1200,9 @@ static int kdb_local(kdb_reason_t reason
 			   instruction_pointer(regs));
 		kdb_dumpregs(regs);
 		break;
+	case KDB_REASON_SYSTEM_NMI:
+		kdb_printf("due to System NonMaskable Interrupt\n");
+		break;
 	case KDB_REASON_NMI:
 		kdb_printf("due to NonMaskable Interrupt @ "
 			   kdb_machreg_fmt "\n",

-- 
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