2022-11-07 14:37:38

by John Ogness

Subject: [PATCH printk v3 11/40] um: kmsg_dumper: use srcu console list iterator

Rather than using the console_lock to guarantee safe console list
traversal, use srcu console list iteration.

Signed-off-by: John Ogness <[email protected]>
---
arch/um/kernel/kmsg_dump.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index f0233e2f8de0..b6acb3837f1d 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -16,16 +16,15 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
struct console *con;
unsigned long flags;
size_t len = 0;
+ int cookie;

/*
* If no consoles are available to output crash information, dump
* the kmsg buffer to stdout.
*/

- if (!console_trylock())
- return;
-
- for_each_console(con) {
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(con) {
/*
* The ttynull console and disabled consoles are ignored
* since they cannot output. All other consoles are
@@ -36,9 +35,7 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
break;
}
}
-
- console_unlock();
-
+ console_srcu_read_unlock(cookie);
if (con)
return;

--
2.30.2

2022-11-09 15:57:31

by Petr Mladek

Subject: Re: [PATCH printk v3 11/40] um: kmsg_dumper: use srcu console list iterator

On Mon 2022-11-07 15:22:09, John Ogness wrote:
> Rather than using the console_lock to guarantee safe console list
> traversal, use srcu console list iteration.

It might be obvious. But I would add:

"It allows to dump the messages even when console_lock() is blocked
during panic()."

It will help to understand this is a clear win.

> Signed-off-by: John Ogness <[email protected]>

After merging with 9th patch for using the racy console_is_enabled(con):

Reviewed-by: Petr Mladek <[email protected]>

Best Regards,
Petr