linux-kernel - [PATCH] CIFS: use the correct length when pinning memory for direct I/O for write

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Date:   Sun, 16 Dec 2018 23:17:04 +0000
From:   Long Li <longli@...uxonhyperv.com>
To:     Steve French <sfrench@...ba.org>, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org
Cc:     Long Li <longli@...rosoft.com>, stable@...r.kernel.org
Subject: [PATCH] CIFS: use the correct length when pinning memory for direct I/O for write

From: Long Li <longli@...rosoft.com>

The current code attempts to pin memory using the largest possible wsize
based on the currect SMB credits. This doesn't cause kernel oops but this is
not optimal as we may pin more pages then actually needed.

Fix this by only pinning what are needed for doing this write I/O.

Signed-off-by: Long Li <longli@...rosoft.com>
Cc: stable@...r.kernel.org
---
 fs/cifs/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 3467351..c23bf9d 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2617,11 +2617,13 @@ cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
 		if (rc)
 			break;
 
+		cur_len = min_t(const size_t, len, wsize);
+
 		if (ctx->direct_io) {
 			ssize_t result;
 
 			result = iov_iter_get_pages_alloc(
-				from, &pagevec, wsize, &start);
+				from, &pagevec, cur_len, &start);
 			if (result < 0) {
 				cifs_dbg(VFS,
 					"direct_writev couldn't get user pages "
-- 
2.7.4