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    SubjectRe: locking question: do_mmap(), do_munmap()


    On Mon, 11 Oct 1999, Stephen C. Tweedie wrote:

    > Hi,
    >
    > On Mon, 11 Oct 1999 20:02:40 +0200, Manfred Spraul
    > <manfreds@colorfullife.com> said:
    >
    > > What about something like a rw-semaphore which protects the vma list:
    > > vma-list modifiers [ie merge_segments(), insert_vm_struct() and
    > > do_munmap()] grab it exclusive, swapper grabs it "shared, starve
    > > exclusive".
    >
    > Deadlock. Process A tries to do an mmap on mm A, gets the exclusive
    > lock, tries to swap out from process B, and grabs mm B's shared lock.
    > Process B in the mean time is doing the same thing and has an exclusive
    > lock on mm B, and is trying to share-lock A. Whoops.

    <looking at the places in question>
    insert_vm_struct doesn't allocate anything.
    Ditto for merge_segments
    In do_munmap() the area that should be protected (ripping the vmas from
    the list) doesn't allocate anything too.
    In the swapper we are protected from recursion, aren't we?


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