[PATCH printk v2 1/5] kdb: do not assume write() callback available

[John Ogness <john.ogness@linutronix.de>]

It is allowed for consoles to provide no write() callback. For
example ttynull does this.

Check if a write() callback is available before using it.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
---
 kernel/debug/kdb/kdb_io.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 5c7e9ba7cd6b..e9139dfc1f0a 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -576,6 +576,8 @@ static void kdb_msg_write(const char *msg, int msg_len)
 			continue;
 		if (c == dbg_io_ops->cons)
 			continue;
+		if (!c->write)
+			continue;
 		/*
 		 * Set oops_in_progress to encourage the console drivers to
 		 * disregard their internal spin locks: in the current calling
-- 
2.30.2