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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.


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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