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    SubjectRe: [PATCH] sysrq: Restore original console_loglevel when sysrq disabled
    On Fri, 11 Jan 2019 22:07:29 +0900
    Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:

    > 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.senozhatsky@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).
    >

    All this is for another patch and another discussion. This current
    patch keeps with what is there and fixes a missing reset of
    console_loglevel.

    Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

    -- Steve

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