libceph: page offset must be less than page size
Currently ceph_msg_data_pages_advance() allows the page offset value
to be PAGE_SIZE, apparently assuming ceph_msg_data_pages_next() will
treat it as 0. But that doesn't happen, and the result led to a
helpful assertion failure.
Change ceph_msg_data_pages_advance() to truncate the offset to 0
before returning if it reaches PAGE_SIZE.
Make a few other minor adjustments in this area (comments and a
better assertion) while modifying it.
This resolves a second issue described in:
http://tracker.ceph.com/issues/4598
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 24f3aba..198b902 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -766,8 +766,8 @@
*length = cursor->resid;
else
*length = (size_t) (bio_vec->bv_len - cursor->vector_offset);
- BUG_ON(*length > PAGE_SIZE);
BUG_ON(*length > cursor->resid);
+ BUG_ON(*page_offset + *length > PAGE_SIZE);
return bio_vec->bv_page;
}
@@ -876,14 +876,13 @@
/* Advance the cursor page offset */
cursor->resid -= bytes;
- cursor->page_offset += bytes;
- if (!bytes || cursor->page_offset & ~PAGE_MASK)
+ cursor->page_offset = (cursor->page_offset + bytes) & ~PAGE_MASK;
+ if (!bytes || cursor->page_offset)
return false; /* more bytes to process in the current page */
- /* Move on to the next page */
+ /* Move on to the next page; offset is already at 0 */
BUG_ON(cursor->page_index >= cursor->page_count);
- cursor->page_offset = 0;
cursor->page_index++;
cursor->last_piece = cursor->resid <= PAGE_SIZE;
@@ -934,8 +933,9 @@
BUG_ON(!cursor->page);
BUG_ON(cursor->offset + cursor->resid != pagelist->length);
+ /* offset of first page in pagelist is always 0 */
*page_offset = cursor->offset & ~PAGE_MASK;
- if (cursor->last_piece) /* pagelist offset is always 0 */
+ if (cursor->last_piece)
*length = cursor->resid;
else
*length = PAGE_SIZE - *page_offset;
@@ -961,7 +961,7 @@
cursor->resid -= bytes;
cursor->offset += bytes;
- /* pagelist offset is always 0 */
+ /* offset of first page in pagelist is always 0 */
if (!bytes || cursor->offset & ~PAGE_MASK)
return false; /* more bytes to process in the current page */