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

[Luis Henriques]

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

    IB/qib: Convert qib_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:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

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
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From a5e1061ca3fa782a97753328d4ce640485b63d59 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack at suse.cz>
Date: Fri, 4 Oct 2013 09:29:12 -0400
Subject: IB/qib: Convert qib_user_sdma_pin_pages() to use
 get_user_pages_fast()

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 at intel.com>
Signed-off-by: Jan Kara <jack at suse.cz>
Signed-off-by: Roland Dreier <roland at purestorage.com>
[bwh: Backported to 3.2:
 - Adjust context
 - Adjust indentation and nr_pages argument in qib_user_sdma_pin_pages()]
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/infiniband/hw/qib/qib_user_sdma.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/infiniband/hw/qib/qib_user_sdma.c b/drivers/infiniband/hw/qib/qib_user_sdma.c
index 8244208..573b460 100644
--- a/drivers/infiniband/hw/qib/qib_user_sdma.c
+++ b/drivers/infiniband/hw/qib/qib_user_sdma.c
@@ -284,8 +284,7 @@ static int qib_user_sdma_pin_pages(const struct qib_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;
@@ -830,10 +829,7 @@ int qib_user_sdma_writev(struct qib_ctxtdata *rcd,
 	while (dim) {
 		const int mxp = 8;

-		down_write(&current->mm->mmap_sem);
 		ret = qib_user_sdma_queue_pkts(dd, pq, &list, iov, dim, mxp);
-		up_write(&current->mm->mmap_sem);
-
 		if (ret <= 0)
 			goto done_unlock;
 		else {
--
1.8.3.2