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    Subject[PATCH 3.11 017/208] IB/qib: Convert qib_user_sdma_pin_pages() to use get_user_pages_fast()
    Date
    3.11.10.3 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Jan Kara <jack@suse.cz>

    commit 603e7729920e42b3c2f4dbfab9eef4878cb6e8fa upstream.

    qib_user_sdma_queue_pkts() gets called with mmap_sem held for
    writing. Except for get_user_pages() deep down in
    qib_user_sdma_pin_pages() we don't seem to need mmap_sem at all. Even
    more interestingly the function qib_user_sdma_queue_pkts() (and also
    qib_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 qib_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.

    Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
    Signed-off-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Roland Dreier <roland@purestorage.com>
    [bwh: Backported to 3.2:
    - Adjust context
    - Adjust indentation and nr_pages argument in qib_user_sdma_pin_pages()]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    drivers/infiniband/hw/qib/qib_user_sdma.c | 6 +-----
    1 file changed, 1 insertion(+), 5 deletions(-)

    diff --git a/drivers/infiniband/hw/qib/qib_user_sdma.c b/drivers/infiniband/hw/qib/qib_user_sdma.c
    index 8244208..573b460 100644
    --- a/drivers/infiniband/hw/qib/qib_user_sdma.c
    +++ b/drivers/infiniband/hw/qib/qib_user_sdma.c
    @@ -284,8 +284,7 @@ static int qib_user_sdma_pin_pages(const struct qib_devdata *dd,
    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;
    @@ -830,10 +829,7 @@ int qib_user_sdma_writev(struct qib_ctxtdata *rcd,
    while (dim) {
    const int mxp = 8;

    - down_write(&current->mm->mmap_sem);
    ret = qib_user_sdma_queue_pkts(dd, pq, &list, iov, dim, mxp);
    - up_write(&current->mm->mmap_sem);
    -
    if (ret <= 0)
    goto done_unlock;
    else {
    --
    1.8.3.2


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