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    SubjectRe: [2.5.20-BUG] 3c59x + highmem + acpi + nfs -> kernel panic
    On Tuesday 04 June 2002 08:37, Andrew Morton wrote:

    > The problem was that pagecache data on the NFS client was showing
    > incorrect chunks of several k's of zeroes. No particuar alignment,
    > either. And it only happened when the machine is under page-replacement
    > pressure. And only when the machine has highmem.
    > It'd be nice to understand _why_ it fixed it. Do we know why NFS
    > was losing data when using KM_USER0? As far as I can see the new
    > and old code look pretty darn similar. Interested.

    Anton's Oops showed that kmap_atomic(page, KM_USER0) is sometimes failing to
    return an address, something that we cannot accept in a networking bottom
    half (performance and reliability would suck if we had to delay and retry).
    That indicates that something is calling kmap_atomic() and then getting
    interrupted before it can call kunmap_atomic().

    >From what I can see, the only other place where KM_USER0 is employed would be
    in the *_highpage() helper routines in include/linux/highmem.h. These
    routines are used in various places, but are usually not protected against
    (soft and hard) interrupts or kernel pre-emption. Could it be that the latter
    is what is causing trouble?

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