ceph: fix race between page writeback and truncate

The client can receive truncate request from MDS at any time.
So the page writeback code need to get i_size, truncate_seq and
truncate_size atomically
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>

fs/ceph/addr.c

@@ -438,13 +438,12 @@ static int writepage_nounlock(struct page *page, struct writeback_control *wbc)
 	struct ceph_inode_info *ci;
 	struct ceph_fs_client *fsc;
 	struct ceph_osd_client *osdc;
-	loff_t page_off = page_offset(page);
-	int len = PAGE_CACHE_SIZE;
-	loff_t i_size;
-	int err = 0;
 	struct ceph_snap_context *snapc, *oldest;
-	u64 snap_size = 0;
+	loff_t page_off = page_offset(page);
 	long writeback_stat;
+	u64 truncate_size, snap_size = 0;
+	u32 truncate_seq;
+	int err = 0, len = PAGE_CACHE_SIZE;
 
 	dout("writepage %p idx %lu\n", page, page->index);
 
@@ -474,13 +473,20 @@ static int writepage_nounlock(struct page *page, struct writeback_control *wbc)
 	}
 	ceph_put_snap_context(oldest);
 
+	spin_lock(&ci->i_ceph_lock);
+	truncate_seq = ci->i_truncate_seq;
+	truncate_size = ci->i_truncate_size;
+	if (!snap_size)
+		snap_size = i_size_read(inode);
+	spin_unlock(&ci->i_ceph_lock);
+
 	/* is this a partial page at end of file? */
-	if (snap_size)
-		i_size = snap_size;
-	else
-		i_size = i_size_read(inode);
-	if (i_size < page_off + len)
-		len = i_size - page_off;
+	if (page_off >= snap_size) {
+		dout("%p page eof %llu\n", page, snap_size);
+		goto out;
+	}
+	if (snap_size < page_off + len)
+		len = snap_size - page_off;
 
 	dout("writepage %p page %p index %lu on %llu~%u snapc %p\n",
 	     inode, page, page->index, page_off, len, snapc);
@@ -494,7 +500,7 @@ static int writepage_nounlock(struct page *page, struct writeback_control *wbc)
 	err = ceph_osdc_writepages(osdc, ceph_vino(inode),
 				   &ci->i_layout, snapc,
 				   page_off, len,
-				   ci->i_truncate_seq, ci->i_truncate_size,
+				   truncate_seq, truncate_size,
 				   &inode->i_mtime, &page, 1);
 	if (err < 0) {
 		dout("writepage setting page/mapping error %d %p\n", err, page);
@@ -631,25 +637,6 @@ static void writepages_finish(struct ceph_osd_request *req,
 	ceph_osdc_put_request(req);
 }
 
-static struct ceph_osd_request *
-ceph_writepages_osd_request(struct inode *inode, u64 offset, u64 *len,
-				struct ceph_snap_context *snapc, int num_ops)
-{
-	struct ceph_fs_client *fsc;
-	struct ceph_inode_info *ci;
-	struct ceph_vino vino;
-
-	fsc = ceph_inode_to_client(inode);
-	ci = ceph_inode(inode);
-	vino = ceph_vino(inode);
-	/* BUG_ON(vino.snap != CEPH_NOSNAP); */
-
-	return ceph_osdc_new_request(&fsc->client->osdc, &ci->i_layout,
-			vino, offset, len, num_ops, CEPH_OSD_OP_WRITE,
-			CEPH_OSD_FLAG_WRITE|CEPH_OSD_FLAG_ONDISK,
-			snapc, ci->i_truncate_seq, ci->i_truncate_size, true);
-}
-
 /*
  * initiate async writeback
  */
@@ -658,7 +645,8 @@ static int ceph_writepages_start(struct address_space *mapping,
 {
 	struct inode *inode = mapping->host;
 	struct ceph_inode_info *ci = ceph_inode(inode);
-	struct ceph_fs_client *fsc;
+	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
+	struct ceph_vino vino = ceph_vino(inode);
 	pgoff_t index, start, end;
 	int range_whole = 0;
 	int should_loop = 1;
@@ -670,7 +658,8 @@ static int ceph_writepages_start(struct address_space *mapping,
 	unsigned wsize = 1 << inode->i_blkbits;
 	struct ceph_osd_request *req = NULL;
 	int do_sync;
-	u64 snap_size;
+	u64 truncate_size, snap_size;
+	u32 truncate_seq;
 
 	/*
 	 * Include a 'sync' in the OSD request if this is a data
@@ -685,7 +674,6 @@ static int ceph_writepages_start(struct address_space *mapping,
 	     wbc->sync_mode == WB_SYNC_NONE ? "NONE" :
 	     (wbc->sync_mode == WB_SYNC_ALL ? "ALL" : "HOLD"));
 
-	fsc = ceph_inode_to_client(inode);
 	if (fsc->mount_state == CEPH_MOUNT_SHUTDOWN) {
 		pr_warning("writepage_start %p on forced umount\n", inode);
 		return -EIO; /* we're in a forced umount, don't write! */
@@ -728,6 +716,14 @@ static int ceph_writepages_start(struct address_space *mapping,
 		snap_size = i_size_read(inode);
 	dout(" oldest snapc is %p seq %lld (%d snaps)\n",
 	     snapc, snapc->seq, snapc->num_snaps);
+
+	spin_lock(&ci->i_ceph_lock);
+	truncate_seq = ci->i_truncate_seq;
+	truncate_size = ci->i_truncate_size;
+	if (!snap_size)
+		snap_size = i_size_read(inode);
+	spin_unlock(&ci->i_ceph_lock);
+
 	if (last_snapc && snapc != last_snapc) {
 		/* if we switched to a newer snapc, restart our scan at the
 		 * start of the original file range. */
@@ -739,7 +735,6 @@ static int ceph_writepages_start(struct address_space *mapping,
 
 	while (!done && index <= end) {
 		int num_ops = do_sync ? 2 : 1;
-		struct ceph_vino vino;
 		unsigned i;
 		int first;
 		pgoff_t next;
@@ -833,17 +828,18 @@ static int ceph_writepages_start(struct address_space *mapping,
 			 * that it will use.
 			 */
 			if (locked_pages == 0) {
-				size_t size;
-
 				BUG_ON(pages);
-
 				/* prepare async write request */
 				offset = (u64)page_offset(page);
 				len = wsize;
-				req = ceph_writepages_osd_request(inode,
-							offset, &len, snapc,
-							num_ops);
-
+				req = ceph_osdc_new_request(&fsc->client->osdc,
+							&ci->i_layout, vino,
+							offset, &len, num_ops,
+							CEPH_OSD_OP_WRITE,
+							CEPH_OSD_FLAG_WRITE |
+							CEPH_OSD_FLAG_ONDISK,
+							snapc, truncate_seq,
+							truncate_size, true);
 				if (IS_ERR(req)) {
 					rc = PTR_ERR(req);
 					unlock_page(page);
@@ -854,8 +850,8 @@ static int ceph_writepages_start(struct address_space *mapping,
 				req->r_inode = inode;
 
 				max_pages = calc_pages_for(0, (u64)len);
-				size = max_pages * sizeof (*pages);
-				pages = kmalloc(size, GFP_NOFS);
+				pages = kmalloc(max_pages * sizeof (*pages),
+						GFP_NOFS);
 				if (!pages) {
 					pool = fsc->wb_pagevec_pool;
 					pages = mempool_alloc(pool, GFP_NOFS);