IB/qib: Convert qib_user_sdma_pin_pages() to use get_user_pages_fast()

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.

Cc: <stable@vger.kernel.org>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 1 insertions, 5 deletions

diff --git a/drivers/infiniband/hw/qib/qib_user_sdma.c b/drivers/infiniband/hw/qib/qib_user_sdma.c
index d0a0ea0c14d6..165aee2ca8a0 100644
--- a/drivers/infiniband/hw/qib/qib_user_sdma.c
+++ b/drivers/infiniband/hw/qib/qib_user_sdma.c
@@ -594,8 +594,7 @@ static int qib_user_sdma_pin_pages(const struct qib_devdata *dd,
                 else
                         j = npages;
 
-                ret = get_user_pages(current, current->mm, addr,
-                             j, 0, 1, pages, NULL);
+                ret = get_user_pages_fast(addr, j, 0, pages);
                 if (ret != j) {
                         i = 0;
                         j = ret;
@@ -1294,11 +1293,8 @@ int qib_user_sdma_writev(struct qib_ctxtdata *rcd,
                 int mxp = 8;
                 int ndesc = 0;
 
-                down_write(&current->mm->mmap_sem);
                 ret = qib_user_sdma_queue_pkts(dd, ppd, pq,
                                 iov, dim, &list, &mxp, &ndesc);
-                up_write(&current->mm->mmap_sem);
-
                 if (ret < 0)
                         goto done_unlock;
                 else {