[PATCH 3.4 20/60] IB/ipath: Convert ipath_user_sdma_pin_pages() to use get_user_pages_fast()

[Greg Kroah-Hartman]

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

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

From: Jan Kara <j...@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 <j...@suse.cz>
Signed-off-by: Mike Marciniszyn <mike.marcinis...@intel.com>
[ Merged in fix for call to get_user_pages_fast from Tetsuo Handa
  <penguin-ker...@i-love.sakura.ne.jp>.  - Roland ]
Signed-off-by: Roland Dreier <rol...@purestorage.com>
Signed-off-by: Greg Kroah-Hartman <gre...@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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