lkml.org 
[lkml]   [2007]   [Oct]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: race with page_referenced_one->ptep_test_and_clear_young and pagetable setup/pulldown
    On Thu, 04 Oct 2007 18:43:32 -0700 Jeremy Fitzhardinge <jeremy@goop.org> wrote:

    > David's change 10a8d6ae4b3182d6588a5809a8366343bc295c20, "i386: add
    > ptep_test_and_clear_{dirty,young}" has introduced an SMP race which
    > affects the Xen pv-ops backend.

    y'know, I think I think it's been several years since I saw a report of an
    honest to goodness, genuine SMP race in core kernel. We used to be
    infested by them, but the term has fallen into disuse. Interesting, but
    OT.

    > It seems to me that there are a few ways to fix this:
    >
    > 1. Use asm-generic/pgtable.h when CONFIG_PARAVIRT is enabled. This
    > will clearly work, but is pretty blunt.
    > 2. Make test_and_clear_pte_flags a new paravirt-op, which can be
    > implemented in Xen as a hypercall, and as a raw test_and_clear_bit
    > for everyone else. The downside is adding yet another pv-op.
    > 3. Restructure the pagetable setup code so that the mm is not added
    > to the prio tree until after arch_dup_mmap has been called (and
    > the converse for exit_mmap). This is arguably cleaner, but I
    > haven't looked to see how much trouble this would be.
    >
    > Thoughts anyone? Does making the pagetables visible "early" cause
    > problems for anyone else?

    I expect that 2) has the maximum niceness*suitable-for-2.6.23 product.

    That's if you actually care much about kernel.org major releases - do many
    people run kernel.org kernels on Xen? If "not many" then we could perhaps
    do something more elaborate for 2.6.23.1. But adding ever more pvops as
    core kernel evolves was always expected.
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-10-05 04:47    [W:3.722 / U:0.432 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site