Messages in this thread | | | Date | Fri, 16 Apr 2004 14:37:26 +1000 | From | David Gibson <> | Subject | Re: Fix bogus get_page() calls in hugepage code |
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On Thu, Apr 15, 2004 at 09:30:11PM -0700, Andrew Morton wrote: > David Gibson <david@gibson.dropbear.id.au> wrote: > > > > On some archs the functions used to implement follow_page() for > > hugepages do a get_page(). This is unlike the normal-page path for > > follow_page(), so presumably a bug. This patch fixes it. > > get_user_pages() is supposed to pin the pages which it placed into the > callers pages[] array. > > And the caller of get_user_pages() is supposed to unpin those pages when > they are finished with. > > So follow_hugetlb_page() is currently doing the right thing. The asymmetry > with follow_page() is awkward, but the overall intent was to minimise the > amount of impact which the hugepage code has on core MM.
Yes, but I'm not talking about follow_hugetlb_page() (my patch doesn't touch it). I'm talking about follow_huge_addr() and follow_huge_pmd(). These are called to implement follow_page(). In get_user_pages(), follow_pages() is bypassed bu the call to follow_hugetlb_page(), but these extra get_pages() are presumably a bug if follow_page() is called on a hugepage from somewhere other than get_user_pages().
So I think my patch is correct.
> Aside: note that get_user_pages() doesn't hold page_table_lock while > walking the pagetables, whereas it does hold that lock while walking the > regular pages' pagetables. This is because the caller of get_user_pages() > holds down_read(mmap_sem), whereas hugetlb pagetable setup and teardown > always happens under down_write(mmap_sem).
Ah, that's useful to know.
-- David Gibson | For every complex problem there is a david AT gibson.dropbear.id.au | solution which is simple, neat and | wrong. http://www.ozlabs.org/people/dgibson - 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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