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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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