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    SubjectRe: [Fdutils] DMA cache consistency bug introduced in 2.6.28


    On Wed, 23 Dec 2009, Andi Kleen wrote:
    >
    > I suspect it's a system where the APIC timer stops in deeper idle
    > states and it supports them. In this case CPU #0 does timer broadcasts
    > when needed to wake the other CPUs up from deep C, but for that it has
    > to run with HPET. At least the other ones can still enjoy the LAPIC
    > timer.

    Ahh, ok, that makes sense. I was assuming the broadcast timer would act in
    that capacity, but..

    > This might suggest that Mark's floppy controller doesn't like
    > deep C? Mark, did you try booting with processor.max_cstate=1
    > and HPET enabled?

    We have indeed had historical issues with floppy and sleep states before.

    I do note another issue, though - the floppy driver itself seems totally
    broken when it comes to using interleaved sectors. Alain, that "place
    logical sectors" code is simply _broken_ - the "while" kicks in only if
    the first sector we test is busy _and_ we were at the last sector so that
    we increment past F_SECT_PER_TRACK.

    So shouldn't that sector layout be something like the appended?

    Linus
    ---
    drivers/block/floppy.c | 7 ++-----
    1 files changed, 2 insertions(+), 5 deletions(-)

    diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
    index 3266b4f..9c9148c 100644
    --- a/drivers/block/floppy.c
    +++ b/drivers/block/floppy.c
    @@ -2237,13 +2237,10 @@ static void setup_format_params(int track)
    for (count = 1; count <= F_SECT_PER_TRACK; ++count) {
    here[n].sect = count;
    n = (n + il) % F_SECT_PER_TRACK;
    - if (here[n].sect) { /* sector busy, find next free sector */
    + while (here[n].sect) { /* sector busy, find next free sector */
    ++n;
    - if (n >= F_SECT_PER_TRACK) {
    + if (n >= F_SECT_PER_TRACK)
    n -= F_SECT_PER_TRACK;
    - while (here[n].sect)
    - ++n;
    - }
    }
    }
    if (_floppy->stretch & FD_SECTBASEMASK) {

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