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    SubjectRe: Change in functionality of futex() system call.
    On Mon, Jun 06, 2011 at 07:11:37PM +0200, Eric Dumazet wrote:
    > Le lundi 06 juin 2011 à 19:05 +0200, Peter Zijlstra a écrit :
    >
    > > Dunno, using futexes on private file maps is stupid imo, its just asking
    > > for trouble, ro private file maps are even worse. Forcing the COW is the
    > > only sane answer in that it gives consistent results and 'breaks' silly
    > > expectations early instead of sometimes.
    > >
    > > Anyway, that's not really the issue here, as David uses MAP_SHARED (as
    > > one should if one is interested in the shared value).
    >
    > Sure, but maybe another guy is 'stupid' and uses MAP_PRIVATE on its
    > read-only mappings. With old kernels this was working, and we were not
    > doing the COW.

    That sounds like a bug in both the kernel and userspace. I would expect
    a MAP_PRIVATE not be seen by any other process regardless. That's the
    definition of PRIVATE.

    From: http://www.gnu.org/s/hello/manual/libc/Memory_002dmapped-I_002fO.html

    MAP_PRIVATE
    This specifies that writes to the region should never be written back
    to the attached file. Instead, a copy is made for the process, and the
    region will be swapped normally if memory runs low. No other process
    will see the changes.

    -- Steve
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