On Sat 2022-09-24 02:10 +0206, John Ogness wrote:
> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>
> Provide a special list iterator macro for KGDB to allow unprotected list
> walks and add a few comments to explain the hope based approach.
>
> Preperatory change for changing the console list to hlist and adding
> lockdep asserts to regular list walks.
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> ---
> drivers/tty/serial/kgdboc.c | 5 ++++-
> include/linux/console.h | 10 ++++++++++
> kernel/debug/kdb/kdb_io.c | 7 ++++++-
> 3 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index af2aa76bae15..57a5fd27dffe 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -462,10 +462,13 @@ static void kgdboc_earlycon_pre_exp_handler(void)
> * we have no other choice so we keep using it. Since not all
> * serial drivers might be OK with this, print a warning once per
> * boot if we detect this case.
> + *
> + * Pretend that walking the console list is safe...
> */
> - for_each_console(con)
> + for_each_console_kgdb(con) {
> if (con == kgdboc_earlycon_io_ops.cons)
> return;
> + }
>
> already_warned = true;
> pr_warn("kgdboc_earlycon is still using bootconsole\n");
> diff --git a/include/linux/console.h b/include/linux/console.h
> index 24344f9b0bc1..86a6125512b9 100644
> --- a/include/linux/console.h
> +++ b/include/linux/console.h
> @@ -187,6 +187,16 @@ extern void console_list_unlock(void) __releases(console_mutex);
> #define for_each_console(con) \
> for (con = console_drivers; con != NULL; con = con->next)
>
> +/**
> + * for_each_console_kgdb() - Iterator over registered consoles for KGDB
> + * @con: struct console pointer used as loop cursor
> + *
> + * Has no serialization requirements and KGDB pretends that this is safe.
> + * Don't use outside of the KGDB fairy tale land!
> + */
> +#define for_each_console_kgdb(con) \
> + for (con = console_drivers; con != NULL; con = con->next)
> +
> extern int console_set_on_cmdline;
> extern struct console *early_console;
>
> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index 67d3c48a1522..fb3775e61a3b 100644
> --- a/kernel/debug/kdb/kdb_io.c
> +++ b/kernel/debug/kdb/kdb_io.c
> @@ -558,7 +558,12 @@ static void kdb_msg_write(const char *msg, int msg_len)
> cp++;
> }
>
> - for_each_console(c) {
> + /*
> + * This is a completely unprotected list walk designed by the
> + * wishful thinking department. See the oops_in_progress comment
> + * below - especially the encourage section...
> + */
> + for_each_console_kgdb(c) {
> if (!(c->flags & CON_ENABLED))
> continue;
> if (c == dbg_io_ops->cons)
> --
> 2.30.2
>
Reviewed-by: Aaron Tomlin <atomlin@xxxxxxxxxx>
--
Aaron Tomlin
