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printk: console_flush_on_panic: use srcu console list iterator

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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>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-20-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2022-11-16 17:27:31 +01:06 committed by Petr Mladek
parent d792db6f6b
commit 87f2e4b7d9
1 changed files with 11 additions and 10 deletions
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21
kernel/printk/printk.c
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@ -3050,21 +3050,22 @@ 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();
}