[PATCH 3.2 043/185] IB/ipath: Convert ipath_user_sdma_pin_pages()to use get_user_pages_fast()

From: Ben Hutchings
Date: Sat Dec 28 2013 - 21:22:41 EST

3.2.54-rc1 review patch. If anyone has any objections, please let me know.


From: Jan Kara <jack@xxxxxxx>

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 <jack@xxxxxxx>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>

[ Merged in fix for call to get_user_pages_fast from Tetsuo Handa
<penguin-kernel@xxxxxxxxxxxxxxxxxxx>. - Roland ]

Signed-off-by: Roland Dreier <roland@xxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
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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