diff mbox series

[printk,v2,26/38] kdb: use srcu console list iterator

Message ID 20221019145600.1282823-27-john.ogness@linutronix.de
State New
Headers
Series reduce console_lock scope |

Commit Message

John Ogness Oct. 19, 2022, 2:55 p.m. UTC 
  Guarantee safe iteration of the console list by using SRCU.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 kernel/debug/kdb/kdb_io.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Doug Anderson Oct. 25, 2022, 12:47 a.m. UTC | #1 
Hi,

On Wed, Oct 19, 2022 at 7:56 AM John Ogness <john.ogness@linutronix.de> wrote:
>
> Guarantee safe iteration of the console list by using SRCU.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  kernel/debug/kdb/kdb_io.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index 550fe8b456ec..5c0bd93c3574 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)
> @@ -558,7 +559,8 @@ static void kdb_msg_write(const char *msg, int msg_len)
>                 cp++;
>         }
>
> -       for_each_console(c) {
> +       cookie = console_srcu_read_lock();
> +       for_each_console_srcu(c) {

Maybe it wouldn't hurt to also have a comment saying that normally the
console_srcu_read_lock() wouldn't be enough given that we're poking
into each individual console and calling ->write() but that we're
relying on the fact that all the other CPUs are stopped at the moment
and thus we should be safe.

-Doug
Petr Mladek Oct. 25, 2022, 2:59 p.m. UTC | #2 
On Mon 2022-10-24 17:47:25, Doug Anderson wrote:
> Hi,
> 
> On Wed, Oct 19, 2022 at 7:56 AM John Ogness <john.ogness@linutronix.de> wrote:
> >
> > Guarantee safe iteration of the console list by using SRCU.
> >
> > Signed-off-by: John Ogness <john.ogness@linutronix.de>
> > ---
> >  kernel/debug/kdb/kdb_io.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> > index 550fe8b456ec..5c0bd93c3574 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)
> > @@ -558,7 +559,8 @@ static void kdb_msg_write(const char *msg, int msg_len)
> >                 cp++;
> >         }
> >
> > -       for_each_console(c) {
> > +       cookie = console_srcu_read_lock();
> > +       for_each_console_srcu(c) {
> 
> Maybe it wouldn't hurt to also have a comment saying that normally the
> console_srcu_read_lock() wouldn't be enough given that we're poking
> into each individual console and calling ->write() but that we're
> relying on the fact that all the other CPUs are stopped at the moment
> and thus we should be safe.

True. I guess that the SRCU lock is not really needed from the same
reason.

Well, the SRCU walk makes sense. It makes sure that the list can be
safely traversed. I mean that pointers are updated and read in
the right order with the right barriers.

Yes, it would be nice to add a comment.

Best Regards,
Petr
diff mbox series

Patch

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 550fe8b456ec..5c0bd93c3574 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)
@@ -558,7 +559,8 @@  static void kdb_msg_write(const char *msg, int msg_len)
 		cp++;
 	}
 
-	for_each_console(c) {
+	cookie = console_srcu_read_lock();
+	for_each_console_srcu(c) {
 		if (!console_is_enabled(c))
 			continue;
 		if (c == dbg_io_ops->cons)
@@ -577,6 +579,7 @@  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)