Commit 87f2e4b7 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: console_flush_on_panic: use srcu console list iterator 



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: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-20-john.ogness@linutronix.de
parent d792db6f

kernel/printk/printk.c

+11 −10
Original line number Diff line number Diff line
@@ -3050,22 +3050,23 @@ 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);



		cookie = console_srcu_read_lock();

		for_each_console_srcu(c) {

			/*

		 * 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.

			 * If the above console_trylock() failed, this is an

			 * unsynchronized assignment. But in that case, the

			 * kernel is in "hope and pray" mode anyway.

			 */

		hlist_for_each_entry_safe(c, tmp, &console_list, node)

			c->seq = seq;

		}

		console_srcu_read_unlock(cookie);

	}

	console_unlock();

}