diff mbox series

[printk,v4,13/39] kdb: use srcu console list iterator

Message ID 20221114162932.141883-14-john.ogness@linutronix.de
State New
Headers
Series reduce console_lock scope |

Commit Message

John Ogness Nov. 14, 2022, 4:29 p.m. UTC 
  Guarantee safe iteration of the console list by using SRCU.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/debug/kdb/kdb_io.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

Comments

Aaron Tomlin Nov. 14, 2022, 9:16 p.m. UTC | #1 
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.ogness@linutronix.de>
> Reviewed-by: Petr Mladek <pmladek@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 <atomlin@atomlin.com>
diff mbox series

Patch

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)