[PATCH v2] kdb: Make kdb_printf robust to run in NMI context

[Sumit Garg]

While rounding up CPUs via NMIs, its possible that a rounded up CPU
maybe holding a console port lock leading to kgdb master CPU stuck in
a deadlock during invocation of console write operations. So in order
to avoid such a deadlock, invoke bust_spinlocks() prior to invocation
of console handlers.

Also, add a check for console port to be enabled prior to invocation of
corresponding handler.

Suggested-by: Petr Mladek <pmla...@suse.com>
Suggested-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
Signed-off-by: Sumit Garg <sumit.g...@linaro.org>
---

Changes in v2:
- Use oops_in_progress directly instead of bust_spinlocks().

 kernel/debug/kdb/kdb_io.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 924bc92..3a5a068 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -699,7 +699,11 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, 
va_list ap)
                        }
                }
                for_each_console(c) {
+                       if (!(c->flags & CON_ENABLED))
+                               continue;
+                       ++oops_in_progress;
                        c->write(c, cp, retlen - (cp - kdb_buffer));
+                       --oops_in_progress;
                        touch_nmi_watchdog();
                }
        }
@@ -761,7 +765,11 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, 
va_list ap)
                        }
                }
                for_each_console(c) {
+                       if (!(c->flags & CON_ENABLED))
+                               continue;
+                       ++oops_in_progress;
                        c->write(c, moreprompt, strlen(moreprompt));
+                       --oops_in_progress;
                        touch_nmi_watchdog();
                }
 
-- 
2.7.4