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    SubjectRe: [PATCH RESEND 1/3] printk: convert byte-buffer to variable-length record buffer
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    On Fri, 2012-05-11 at 02:38 +0200, Kay Sievers wrote:
    > On Thu, May 10, 2012 at 10:52 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
    >
    > > The change to verify that 'current' matches the previous printout is
    > > so far the *only* sane semantic change I've seen in this thread.
    > > Everything else has been pure garbage.
    >
    > Ok, let's continue with sane things then. :)
    >
    > Here is a stupid kernel module which creates 3 racy printk() loops, 2 of
    > them do continuation, one does an atomic print. The continuation one
    > prints one char per printk.
    > http://people.freedesktop.org/~kay/printk-race/printk-race.c
    >
    > The lines all try to look like:
    > (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    > (CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC)
    > (XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX)
    >
    > Every loop has it's own uppercase character. The line enclosed in '()'.
    > 'A' is the atomic one, the cont ones are 'C' and 'X'.

    Having only one continuation user racing against an atomic printk user
    looks like this:

    Current kernel:
    [ 54.062900] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 54.068200] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 54.071698] (CC(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 54.074103] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 54.076052] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 54.078116] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 54.080096] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 54.082060] CC(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 54.086121] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    http://people.freedesktop.org/~kay/printk-race/printk-out-before-2.txt

    Record buffer, with cont buffer owner:
    [ 33.431129] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.435112] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.439131] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.441820] (CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC)
    [ 33.445292] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.450131] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.453127] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.456084] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.459143] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.462161] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 33.465165] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    http://people.freedesktop.org/~kay/printk-race/printk-out-after-2.txt

    Kay



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