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    SubjectRe: [PATCH 2/2] printk: wake up klogd in vprintk_emit
    On Sat, 14 Apr 2018 12:01:45 +0900
    Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:

    > --- a/kernel/printk/printk.c
    > +++ b/kernel/printk/printk.c
    > @@ -1888,6 +1888,7 @@ asmlinkage int vprintk_emit(int facility, int level,
    >
    > printed_len = log_output(facility, level, lflags, dict, dictlen, text, text_len);
    >
    > + wake_up_klogd();
    > logbuf_unlock_irqrestore(flags);

    You can't do this, because the scheduler can call printk_deferred()
    with the rq lock held, and printk_deferred() will grab the logbuf lock.

    Calling wake_up_klogd() will grab the rq lock and give us a A-B<->B-A
    locking order.

    -- Steve

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