[3.5.y.z extended stable] Patch "IB/ipath: Convert ipath_user_sdma_pin_pages() to use" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Fri Nov 29 14:03:08 UTC 2013

This is a note to let you know that I have just added a patch titled

    IB/ipath: Convert ipath_user_sdma_pin_pages() to use

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From b8bb3664df3dcf6f53f64e098707b7923d6f60aa Mon Sep 17 00:00:00 2001
From: Jan Kara <jack at suse.cz>
Date: Fri, 4 Oct 2013 09:29:06 -0400
Subject: IB/ipath: Convert ipath_user_sdma_pin_pages() to use

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 at suse.cz>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn at intel.com>

[ Merged in fix for call to get_user_pages_fast from Tetsuo Handa
  <penguin-kernel at I-love.SAKURA.ne.jp>.  - Roland ]

Signed-off-by: Roland Dreier <roland at purestorage.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 drivers/infiniband/hw/ipath/ipath_user_sdma.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/infiniband/hw/ipath/ipath_user_sdma.c b/drivers/infiniband/hw/ipath/ipath_user_sdma.c
index f5cb13b..cc04b7b 100644
--- 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(const struct ipath_devdata *dd,
 	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_devdata *dd,
 	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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