[PATCH 3.12 061/212] IB/qib: Convert qib_user_sdma_pin_pages() to use get_user_pages_fast()

[Greg Kroah-Hartman]

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

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

From: Jan Kara <jack@xxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Roland Dreier <roland@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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
@@ -594,8 +594,7 @@ static int qib_user_sdma_pin_pages(const
 		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_ctxt
 		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 {


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