kdb: Add support for external NMI handler to call KGDB/KDB

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@sgi.com>
Acked-by: Jason Wessel <jason.wessel@windriver.com>
Reviewed-by: Dimitri Sivanich <sivanich@sgi.com>
Reviewed-by: Hedi Berriche <hedi@sgi.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Link: http://lkml.kernel.org/r/20131002151417.928886849@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/kdb.h b/include/linux/kdb.h
index 7f6fe6e015bc..290db1269c4c 100644
--- a/include/linux/kdb.h
+++ b/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;
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index c6e091bf39a5..dfb4f2ffdaa2 100644
--- a/include/linux/kgdb.h
+++ b/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;