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    Subject[PATCH 3.10 051/173] IB/ipath: Convert ipath_user_sdma_pin_pages() to use get_user_pages_fast()
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jan Kara <jack@suse.cz>

    commit 4adcf7fb6783e354aab38824d803fa8c4f8e8a27 upstream.

    ipath_user_sdma_queue_pkts() gets called with mmap_sem held for
    writing. Except for get_user_pages() deep down in
    ipath_user_sdma_pin_pages() we don't seem to need mmap_sem at all.

    Even more interestingly the function ipath_user_sdma_queue_pkts() (and
    also ipath_user_sdma_coalesce() called somewhat later) call
    copy_from_user() which can hit a page fault and we deadlock on trying
    to get mmap_sem when handling that fault. So just make
    ipath_user_sdma_pin_pages() use get_user_pages_fast() and leave
    mmap_sem locking for mm.

    This deadlock has actually been observed in the wild when the node
    is under memory pressure.

    Signed-off-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
    [ Merged in fix for call to get_user_pages_fast from Tetsuo Handa
    <penguin-kernel@I-love.SAKURA.ne.jp>. - Roland ]
    Signed-off-by: Roland Dreier <roland@purestorage.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/infiniband/hw/ipath/ipath_user_sdma.c | 7 +------
    1 file changed, 1 insertion(+), 6 deletions(-)

    --- a/drivers/infiniband/hw/ipath/ipath_user_sdma.c
    +++ b/drivers/infiniband/hw/ipath/ipath_user_sdma.c
    @@ -280,9 +280,7 @@ static int ipath_user_sdma_pin_pages(con
    int j;
    int ret;

    - ret = get_user_pages(current, current->mm, addr,
    - npages, 0, 1, pages, NULL);
    -
    + ret = get_user_pages_fast(addr, npages, 0, pages);
    if (ret != npages) {
    int i;

    @@ -811,10 +809,7 @@ int ipath_user_sdma_writev(struct ipath_
    while (dim) {
    const int mxp = 8;

    - down_write(&current->mm->mmap_sem);
    ret = ipath_user_sdma_queue_pkts(dd, pq, &list, iov, dim, mxp);
    - up_write(&current->mm->mmap_sem);
    -
    if (ret <= 0)
    goto done_unlock;
    else {



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