[PATCH 3.10 24/26] IB/qib: Convert qib_user_sdma_pin_pages() to use get_user_pages_fast()

[Greg Kroah-Hartman]

3.10-stable review patch.  If anyone has any objections, please let me know.

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

From: Jan Kara <j...@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.marcinis...@intel.com>
Signed-off-by: Jan Kara <j...@suse.cz>
Signed-off-by: Roland Dreier <rol...@purestorage.com>
[Backported to 3.10: (Thanks to Ben Huthings)
 - Adjust context
 - Adjust indentation and nr_pages argument in qib_user_sdma_pin_pages()]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
Signed-off-by: Mike Marciniszyn <mike.marcinis...@intel.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/infiniband/hw/qib/qib_user_sdma.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- 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
        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_ctxt
        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 {


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