Messages in this thread | | | Date | Mon, 06 Jun 2011 10:56:13 -0700 | From | Darren Hart <> | Subject | Re: Change in functionality of futex() system call. |
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On 06/06/2011 10:27 AM, Steven Rostedt wrote: > 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.
This doesn't address what happens if changes to a MAP_SHARED mapping are visible to a MAP_PRIVATE mapping, which is more the issue at hand I believe.
-- Darren Hart Intel Open Source Technology Center Yocto Project - Linux Kernel -- 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/
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