libceph: only kunmap kmapped pages

(cherry picked from commit 5ce765a540f34d1e2005e1210f49f67fdf11e997)

In write_partial_msg_pages(), pages need to be kmapped in order to
perform a CRC-32c calculation on them.  As an artifact of the way
this code used to be structured, the kunmap() call was separated
from the kmap() call and both were done conditionally.  But the
conditions under which the kmap() and kunmap() calls were made
differed, so there was a chance a kunmap() call would be done on a
page that had not been mapped.

The symptom of this was tripping a BUG() in kunmap_high() when
pkmap_count[nr] became 0.

Reported-by: Bryan K. Wright <bryan@virginia.edu>
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 5f312510f49caf1cc525d44dd084ce281dda0ec1..6577a9fc6ce7bd1c7555b183daca389feb02fb4d 100644 (file)
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -1069,16 +1069,13 @@ static int write_partial_msg_pages(struct ceph_connection *con)
                        BUG_ON(kaddr == NULL);
                        base = kaddr + con->out_msg_pos.page_pos + bio_offset;
                        crc = crc32c(crc, base, len);
+                       kunmap(page);
                        msg->footer.data_crc = cpu_to_le32(crc);
                        con->out_msg_pos.did_page_crc = true;
                }
                ret = ceph_tcp_sendpage(con->sock, page,
                                      con->out_msg_pos.page_pos + bio_offset,
                                      len, 1);
-
-               if (do_datacrc)
-                       kunmap(page);
-
                if (ret <= 0)
                        goto out;