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    SubjectRe: [PATCH RESEND 1/3] printk: convert byte-buffer to variable-length record buffer
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    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'.

    Our current kernel look like:
    [ 99.056806] XC(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 99.059772] XC(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 99.062168] XCCX(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 99.066479] CXXC(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 99.070063] XC(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 99.073081] XCCXCXCXCXCXCXCXCXCXCXCXCXCXCXCCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXC)
    [ 99.148325] (CCXCXCX)
    [ 99.155468] (XXCXCXCXCCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXCXXCXCXCXCXCXCXCXCXC)
    [ 99.277357] (CCXCXCXCX)
    http://people.freedesktop.org/~kay/printk-race/printk-out-before.txt


    The kernel with the record buffer, and the 'current' who owns the cont buffer
    looks like:
    [ 78.080866] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 78.082790] (CC
    [ 78.084152] (XX
    [ 78.084497] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 78.085494] C
    [ 78.086125] X
    [ 78.087188] C
    [ 78.088669] X
    [ 78.089803] C
    [ 78.091510] X
    [ 78.091924] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
    [ 78.094112] CC
    [ 78.096171] X
    http://people.freedesktop.org/~kay/printk-race/printk-out-after.txt

    Thanks,
    Kay



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