From: John Ogness <john.ogness@xxxxxxxxxxxxx> commit 6d3e0d8cc63221dec670d0ee92ac57961581e975 upstream. It is allowed for consoles to not provide a write() callback. For example ttynull does this. Check if a write() callback is available before using it. Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx> Reviewed-by: Petr Mladek <pmladek@xxxxxxxx> Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx> Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx> Acked-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx> Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> Signed-off-by: Petr Mladek <pmladek@xxxxxxxx> Link: https://lore.kernel.org/r/20230717194607.145135-2-john.ogness@xxxxxxxxxxxxx Cc: Brian Norris <briannorris@xxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/debug/kdb/kdb_io.c | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -577,6 +577,8 @@ 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 Patches currently in stable-queue which might be from john.ogness@xxxxxxxxxxxxx are queue-5.10/kdb-do-not-assume-write-callback-available.patch
