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    SubjectRe: [RFC][PATCH] Avoid vmtruncate/mmap-page-fault race
    On Thu, May 29, 2003 at 05:33:04PM +0100, Hugh Dickins wrote:
    > On Thu, 29 May 2003, Paul E. McKenney wrote:
    > > On Fri, May 23, 2003 at 11:42:02AM -0700, Paul E. McKenney wrote:
    > > >
    > > > Exactly -- allows a ->nopage() to drop some lock to avoid races
    > > > between pagefault and either vmtruncate() or invalidate_mmap_range().
    > > > This race (from the cross-host mmap viewpoint) is described in:
    > > >
    > > > http://marc.theaimsgroup.com/?l=linux-kernel&m=105286345316249&w=2
    > >
    > > Rediffed for 2.5.70-mm1.
    >
    > Me? I much preferred your original, much sparer, nopagedone patch
    > (labelled "uglyh as hell" by hch). I dislike passing lots of args
    > down a level so they can be passed up again to the library function.
    >
    > In particular, I feel queasy (fear loss of control) about passing a
    > pmd_t* down to a filesystem, which I'd prefer to have no access to
    > such. But I may be in a minority, and the decision won't be mine.

    Fine by me either way. ;-) Here is the rediffed nopagedone patch
    for 2.5.70-mm1.

    Thanx, Paul


    diff -urN -X dontdiff linux-2.5.70-mm1/include/linux/mm.h linux-2.5.70-mm1.nopagedone/include/linux/mm.h
    --- linux-2.5.70-mm1/include/linux/mm.h 2003-05-28 20:16:04.000000000 -0700
    +++ linux-2.5.70-mm1.nopagedone/include/linux/mm.h 2003-05-29 19:34:55.000000000 -0700
    @@ -143,6 +143,7 @@
    void (*open)(struct vm_area_struct * area);
    void (*close)(struct vm_area_struct * area);
    struct page * (*nopage)(struct vm_area_struct * area, unsigned long address, int unused);
    + void (*nopagedone)(struct vm_area_struct * area, unsigned long address, int status);
    int (*populate)(struct vm_area_struct * area, unsigned long address, unsigned long len, pgprot_t prot, unsigned long pgoff, int nonblock);
    };

    diff -urN -X dontdiff linux-2.5.70-mm1/mm/memory.c linux-2.5.70-mm1.nopagedone/mm/memory.c
    --- linux-2.5.70-mm1/mm/memory.c 2003-05-28 20:16:04.000000000 -0700
    +++ linux-2.5.70-mm1.nopagedone/mm/memory.c 2003-05-29 19:34:55.000000000 -0700
    @@ -1468,6 +1468,9 @@
    ret = VM_FAULT_OOM;
    out:
    pte_chain_free(pte_chain);
    + if (vma->vm_ops && vma->vm_ops->nopagedone) {
    + vma->vm_ops->nopagedone(vma, address & PAGE_MASK, ret);
    + }
    return ret;
    }

    -
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