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From:   John Ogness <john.ogness@linutronix.de>
To:     Petr Mladek <pmladek@suse.com>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org,
        Jason Wessel <jason.wessel@windriver.com>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Douglas Anderson <dianders@chromium.org>,
        Aaron Tomlin <atomlin@atomlin.com>,
        kgdb-bugreport@lists.sourceforge.net
Subject: [PATCH printk v2 1/5] kdb: do not assume write() callback available
Date:   Mon, 10 Jul 2023 15:51:20 +0206
Message-Id: <20230710134524.25232-2-john.ogness@linutronix.de>
In-Reply-To: <20230710134524.25232-1-john.ogness@linutronix.de>
References: <20230710134524.25232-1-john.ogness@linutronix.de>
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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