diff mbox series

[printk,v2,29/38] printk: console_flush_on_panic: use srcu console list iterator

Message ID 20221019145600.1282823-30-john.ogness@linutronix.de
State New
Headers
Series reduce console_lock scope |

Commit Message

John Ogness Oct. 19, 2022, 2:55 p.m. UTC 
  With SRCU it is now safe to traverse the console list, even if
the console_trylock() failed. However, overwriting console->seq
when console_trylock() failed is still an issue.

Switch to SRCU iteration and document remaining issue with
console->seq.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 kernel/printk/printk.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

Comments

Petr Mladek Oct. 25, 2022, 3:32 p.m. UTC | #1 
On Wed 2022-10-19 17:01:51, John Ogness wrote:
> With SRCU it is now safe to traverse the console list, even if
> the console_trylock() failed. However, overwriting console->seq
> when console_trylock() failed is still an issue.
> 
> Switch to SRCU iteration and document remaining issue with
> console->seq.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr
diff mbox series

Patch

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 0c37ab208395..e478cb92e7ba 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2998,21 +2998,22 @@  void console_flush_on_panic(enum con_flush_mode mode)
 	console_may_schedule = 0;
 
 	if (mode == CONSOLE_REPLAY_ALL) {
-		struct hlist_node *tmp;
 		struct console *c;
+		int cookie;
 		u64 seq;
 
 		seq = prb_first_valid_seq(prb);
-		/*
-		 * This cannot use for_each_console() because it's not established
-		 * that the current context has console locked and neither there is
-		 * a guarantee that there is no concurrency in that case.
-		 *
-		 * Open code it for documentation purposes and pretend that
-		 * it works.
-		 */
-		hlist_for_each_entry_safe(c, tmp, &console_list, node)
+
+		cookie = console_srcu_read_lock();
+		for_each_console_srcu(c) {
+			/*
+			 * If the above console_trylock() failed, this is an
+			 * unsynchronized assignment. But in that case, the
+			 * kernel is in "hope and pray" mode anyway.
+			 */
 			c->seq = seq;
+		}
+		console_srcu_read_unlock(cookie);
 	}
 	console_unlock();
 }