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    SubjectRe: VM-related Oops: 2.4.15pre1
    On Sat, Nov 17, 2001 at 10:24:44PM -0800, Linus Torvalds wrote:
    >
    > On Sun, 18 Nov 2001, Andrea Arcangeli wrote:
    > >
    > > I also agree the patch shouldn't matter, but one suspect thing is the
    > > fact add_to_swap_cache goes to clobber in a non atomic manner the page
    > > lock.
    >
    > .. you mean __add_to_page_cache(), not add_to_swap_cache().
    >
    > And nope, not really. It does use plain stores to page->flags, and I agree
    > that it is ugly, but if the page was locked before calling it, all the
    > stores will be with the PG_lock bit set - and even plain stores _are_
    > documented to be atomic on x86 (and on all other reasonable architectures
    > too).

    I know all is right if GCC just overwrites the page->flags with data
    that keeps PG_locked set. But GCC doesn't guarantee that. GCC can as
    well do:

    flags = page->flags;
    page->flags = 0;

    change flags here

    page->flags = flags

    probably gcc doesn't, but that's still a kernel bug.

    Andrea
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