On (01/11/19 13:45), Petr Mladek wrote:
> The sysrq header line is printed with an increased loglevel
> to provide users some positive feedback.
>
> The original loglevel is not restored when the sysrq operation
> is disabled. This bug was introduced in 2.6.12 (pre-git-history)
> by the commit ("Allow admin to enable only some of the Magic-Sysrq
> functions").
Good find, and the patch looks OK to me. A small comment below.
FWIW,
Reviewed-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
---
A side note (nitpick, etc.); it's Friday night in here, I'm enjoying
my beer; so maybe I'm wrong about the whole thing.
> @@ -553,6 +553,7 @@ void __handle_sysrq(int key, bool check_mask)
> op_p->handler(key);
> } else {
> pr_cont("This sysrq operation is disabled.\n");
> + console_loglevel = orig_log_level;
> }
This looks a bit racy.
When we do
printk("FOO\n");
console_loglevel = XYZ;
We don't have any real guarantees that printk("FOO\n") will print
anything straight ahead. It is possible that console_sem is already
locked and the owner is preempted, so by the time the console_sem
owner picks up that FOO\n messages, console_loglevel is back to
orig_log_level and suppress_message_printing() will just tell us
to skip the message.
Do we need pr_cont() there? Maybe we can just have a normal pr_err()
which would always tell that "key" sysrq is disabled? (we also
would need to change the error message a bit).
-ss
