2022-11-16 16:36:48

by John Ogness

Subject: [PATCH printk v5 14/40] kdb: use srcu console list iterator

Guarantee safe iteration of the console list by using SRCU.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Reviewed-by: Aaron Tomlin <[email protected]>
---
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

2022-11-17 01:25:13

by Doug Anderson

Subject: Re: [PATCH printk v5 14/40] kdb: use srcu console list iterator

Hi,

On Wed, Nov 16, 2022 at 8:22 AM John Ogness <[email protected]> wrote:
>
> Guarantee safe iteration of the console list by using SRCU.
>
> Signed-off-by: John Ogness <[email protected]>
> Reviewed-by: Petr Mladek <[email protected]>
> Reviewed-by: Aaron Tomlin <[email protected]>
> ---
> kernel/debug/kdb/kdb_io.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)

Without becoming an expert on this whole series, this seems reasonable to me.

Reviewed-by: Douglas Anderson <[email protected]>