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SubjectRe: linux.git: printk() problem
On Sun, Oct 23, 2016 at 11:11:18AM -0700, Linus Torvalds wrote:
>
> For example, one of the really historical uses for partial lines is this:
>
> pr_info("Checking 'hlt' instruction... ");
>
> if (!boot_cpu_data.hlt_works_ok) {
> pr_cont("disabled\n");
> return;
> }
> halt();
> halt();
> halt();
> halt();
> pr_cont("OK\n");
>
> and the point was that there used to be some really old i386 machines
> that hung on the "hlt" instruction (probably not because of a CPU bug,
> but because of either power supply issues or some DMA issues).
>
> To support that, we really *had* to print out the continuation lines
> even when they were partial. And that complicates the printk logic a
> lot.

Note, my ftrace start up tests still does exactly this (e.g.):

pr_info("Testing dynamic ftrace ops: #%d: ", cnt);

[ do lots of testing ]

printk(KERN_CONT "PASSED\n");

Previously a change was made to buffer lines without \n, and I wasted an
entire day debugging why a crash happened because I was looking at the wrong
test.

-- Steve

>
> Now, that "hlt" case is long long gone, and maybe we should just say
> "screw that". It would be really quite easy to say "we don't print out
> continuation lines immediately, we just buffer them for 0.1s instead,
> and KERN_CONT only works for things that really happen more or less
> immediately".
>
> Maybe that really is the right answer. Because the original cause of
> us having to bend over backwards in this case is really no longer
> there. And it would simplify printk a *lot*.
>
> Let me whip up a minimal patch for you to try.

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