On Mon 2022-11-14 17:35 +0106, John Ogness wrote:
> Guarantee safe iteration of the console list by using SRCU.
>
> Signed-off-by: John Ogness <john.ogn...@linutronix.de>
> Reviewed-by: Petr Mladek <pmla...@suse.com>
> ---
> kernel/debug/kdb/kdb_io.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index 67d3c48a1522..5c7e9ba7cd6b 100644
> --- a/kernel/debug/kdb/kdb_io.c
> +++ b/kernel/debug/kdb/kdb_io.c
> @@ -545,6 +545,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
> {
> struct console *c;
> const char *cp;
> + int cookie;
> int len;
>
> if (msg_len == 0)
> @@ -558,8 +559,20 @@ static void kdb_msg_write(const char *msg, int msg_len)
> cp++;
> }
>
> - for_each_console(c) {
> - if (!(c->flags & CON_ENABLED))
> + /*
> + * The console_srcu_read_lock() only provides safe console list
> + * traversal. The use of the ->write() callback relies on all other
> + * CPUs being stopped at the moment and console drivers being able to
> + * handle reentrance when @oops_in_progress is set.
> + *
> + * There is no guarantee that every console driver can handle
> + * reentrance in this way; the developer deploying the debugger
> + * is responsible for ensuring that the console drivers they
> + * have selected handle reentrance appropriately.
> + */
> + cookie = console_srcu_read_lock();
> + for_each_console_srcu(c) {
> + if (!(console_srcu_read_flags(c) & CON_ENABLED))
> continue;
> if (c == dbg_io_ops->cons)
> continue;
> @@ -577,6 +590,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
> --oops_in_progress;
> touch_nmi_watchdog();
> }
> + console_srcu_read_unlock(cookie);
> }
>
> int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
> --
> 2.30.2
>
Reviewed-by: Aaron Tomlin <atom...@atomlin.com>
--
Aaron Tomlin
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