linux-kernel - [PATCH 24/26] ib: Convert qib_user_sdma_pin_pages() to use get_user_pages

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Date:	Wed,  2 Oct 2013 16:28:05 +0200
From:	Jan Kara <jack@...e.cz>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	linux-mm@...ck.org, Jan Kara <jack@...e.cz>,
	Mike Marciniszyn <infinipath@...el.com>,
	Roland Dreier <roland@...nel.org>, linux-rdma@...r.kernel.org
Subject: [PATCH 24/26] ib: Convert qib_user_sdma_pin_pages() to use get_user_pages_unlocked()

Function 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_unlocked() and leave mmap_sem locking for mm.

CC: Mike Marciniszyn <infinipath@...el.com>
CC: Roland Dreier <roland@...nel.org>
CC: linux-rdma@...r.kernel.org
Signed-off-by: Jan Kara <jack@...e.cz>
---
 drivers/infiniband/hw/qib/qib_user_sdma.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/hw/qib/qib_user_sdma.c b/drivers/infiniband/hw/qib/qib_user_sdma.c
index d0a0ea0c14d6..c1b6463acd59 100644
--- a/drivers/infiniband/hw/qib/qib_user_sdma.c
+++ b/drivers/infiniband/hw/qib/qib_user_sdma.c
@@ -594,8 +594,8 @@ static int qib_user_sdma_pin_pages(const struct qib_devdata *dd,
 		else
 			j = npages;
 
-		ret = get_user_pages(current, current->mm, addr,
-			     j, 0, 1, pages, NULL);
+		ret = get_user_pages_unlocked(current, current->mm, addr,
+			 		      j, 0, 1, pages);
 		if (ret != j) {
 			i = 0;
 			j = ret;
@@ -1294,11 +1294,8 @@ int qib_user_sdma_writev(struct qib_ctxtdata *rcd,
 		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 {
-- 
1.8.1.4

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