Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 25 Apr 2005 13:54:01 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH][RFC][0/4] InfiniBand userspace verbs implementation |
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Roland Dreier <roland@topspin.com> wrote: > > Timur> With mlock(), we don't need to use get_user_pages() at all. > Timur> Arjan tells me the only time an mlocked page can move is > Timur> with hot (un)plug of memory, but that isn't supported on > Timur> the systems that we support. We actually prefer mlock() > Timur> over get_user_pages(), because if the process dies, the > Timur> locks automatically go away too. > > There actually is another way pages can move, with both > get_user_pages() and mlock(): copy-on-write after a fork(). If > userspace does a fork(), then all PTEs are marked read-only, and if > the original process touches the page after the fork(), a new page > will be allocated and mapped at the original virtual address.
Do we care about that? A straightforward scenario under which this can happen is:
a) app starts some read I/O in an asynchronous manner b) app forks c) child writes to one of the pages which is still under read I/O d) the read I/O completes e) the child is left with the old data plus the child's modification instead of the new data
which is a very silly application which is giving itself unpredictable memory contents anyway.
I assume there's a more sensible scenario? - 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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