From: John Ogness <john.ogness@linutronix.de> Date: Fri, 24 Feb 2023 15:23:51 +0000 Subject: [PATCH 01/24] kdb: do not assume write() callback available 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> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- kernel/debug/kdb/kdb_io.c | 2 ++ 1 file changed, 2 insertions(+) Index: linux-6.3.0-rt11/kernel/debug/kdb/kdb_io.c =================================================================== @ linux-6.3.0-rt11/kernel/debug/kdb/kdb_io.c:579 @ static void kdb_msg_write(const char *ms 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