ceph: Fix i_size update race

ceph_aio_write() has an optimization that marks cap EPH_CAP_FILE_WR
dirty before data is copied to page cache and inode size is updated.
If ceph_check_caps() flushes the dirty cap before the inode size is
updated, MDS can miss the new inode size. The fix is move
ceph_{get,put}_cap_refs() into ceph_write_{begin,end}() and call
__ceph_mark_dirty_caps() after inode size is updated.
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Sage Weil <sage@inktank.com>

fs/ceph/addr.c

@@ -1078,23 +1078,51 @@ static int ceph_write_begin(struct file *file, struct address_space *mapping,
 			    struct page **pagep, void **fsdata)
 {
 	struct inode *inode = file->f_dentry->d_inode;
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct ceph_file_info *fi = file->private_data;
 	struct page *page;
 	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
-	int r;
+	int r, want, got = 0;
+
+	if (fi->fmode & CEPH_FILE_MODE_LAZY)
+		want = CEPH_CAP_FILE_BUFFER | CEPH_CAP_FILE_LAZYIO;
+	else
+		want = CEPH_CAP_FILE_BUFFER;
+
+	dout("write_begin %p %llx.%llx %llu~%u getting caps. i_size %llu\n",
+	     inode, ceph_vinop(inode), pos, len, inode->i_size);
+	r = ceph_get_caps(ci, CEPH_CAP_FILE_WR, want, &got, pos+len);
+	if (r < 0)
+		return r;
+	dout("write_begin %p %llx.%llx %llu~%u  got cap refs on %s\n",
+	     inode, ceph_vinop(inode), pos, len, ceph_cap_string(got));
+	if (!(got & (CEPH_CAP_FILE_BUFFER|CEPH_CAP_FILE_LAZYIO))) {
+		ceph_put_cap_refs(ci, got);
+		return -EAGAIN;
+	}
 
 	do {
 		/* get a page */
 		page = grab_cache_page_write_begin(mapping, index, 0);
-		if (!page)
-			return -ENOMEM;
-		*pagep = page;
+		if (!page) {
+			r = -ENOMEM;
+			break;
+		}
 
 		dout("write_begin file %p inode %p page %p %d~%d\n", file,
 		     inode, page, (int)pos, (int)len);
 
 		r = ceph_update_writeable_page(file, pos, len, page);
+		if (r)
+			page_cache_release(page);
 	} while (r == -EAGAIN);
 
+	if (r) {
+		ceph_put_cap_refs(ci, got);
+	} else {
+		*pagep = page;
+		*(int *)fsdata = got;
+	}
 	return r;
 }
 
@@ -1108,10 +1136,12 @@ static int ceph_write_end(struct file *file, struct address_space *mapping,
 			  struct page *page, void *fsdata)
 {
 	struct inode *inode = file->f_dentry->d_inode;
+	struct ceph_inode_info *ci = ceph_inode(inode);
 	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
 	struct ceph_mds_client *mdsc = fsc->mdsc;
 	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
 	int check_cap = 0;
+	int got = (unsigned long)fsdata;
 
 	dout("write_end file %p inode %p page %p %d~%d (%d)\n", file,
 	     inode, page, (int)pos, (int)copied, (int)len);
@@ -1134,6 +1164,19 @@ static int ceph_write_end(struct file *file, struct address_space *mapping,
 	up_read(&mdsc->snap_rwsem);
 	page_cache_release(page);
 
+	if (copied > 0) {
+		int dirty;
+		spin_lock(&ci->i_ceph_lock);
+		dirty = __ceph_mark_dirty_caps(ci, CEPH_CAP_FILE_WR);
+		spin_unlock(&ci->i_ceph_lock);
+		if (dirty)
+			__mark_inode_dirty(inode, dirty);
+	}
+
+	dout("write_end %p %llx.%llx %llu~%u  dropping cap refs on %s\n",
+	     inode, ceph_vinop(inode), pos, len, ceph_cap_string(got));
+	ceph_put_cap_refs(ci, got);
+
 	if (check_cap)
 		ceph_check_caps(ceph_inode(inode), CHECK_CAPS_AUTHONLY, NULL);
 

fs/ceph/file.c

@@ -712,63 +712,53 @@ static ssize_t ceph_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	struct ceph_osd_client *osdc =
 		&ceph_sb_to_client(inode->i_sb)->client->osdc;
 	loff_t endoff = pos + iov->iov_len;
-	int want, got = 0;
-	int ret, err;
+	int got = 0;
+	int ret, err, written;
 
 	if (ceph_snap(inode) != CEPH_NOSNAP)
 		return -EROFS;
 
 retry_snap:
+	written = 0;
 	if (ceph_osdmap_flag(osdc->osdmap, CEPH_OSDMAP_FULL))
 		return -ENOSPC;
 	__ceph_do_pending_vmtruncate(inode);
-	dout("aio_write %p %llx.%llx %llu~%u getting caps. i_size %llu\n",
-	     inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
-	     inode->i_size);
-	if (fi->fmode & CEPH_FILE_MODE_LAZY)
-		want = CEPH_CAP_FILE_BUFFER | CEPH_CAP_FILE_LAZYIO;
-	else
-		want = CEPH_CAP_FILE_BUFFER;
-	ret = ceph_get_caps(ci, CEPH_CAP_FILE_WR, want, &got, endoff);
-	if (ret < 0)
-		goto out_put;
-
-	dout("aio_write %p %llx.%llx %llu~%u  got cap refs on %s\n",
-	     inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
-	     ceph_cap_string(got));
-
-	if ((got & (CEPH_CAP_FILE_BUFFER|CEPH_CAP_FILE_LAZYIO)) == 0 ||
-	    (iocb->ki_filp->f_flags & O_DIRECT) ||
-	    (inode->i_sb->s_flags & MS_SYNCHRONOUS) ||
-	    (fi->flags & CEPH_F_SYNC)) {
-		ret = ceph_sync_write(file, iov->iov_base, iov->iov_len,
-			&iocb->ki_pos);
-	} else {
-		/*
-		 * buffered write; drop Fw early to avoid slow
-		 * revocation if we get stuck on balance_dirty_pages
-		 */
-		int dirty;
-
-		spin_lock(&ci->i_ceph_lock);
-		dirty = __ceph_mark_dirty_caps(ci, CEPH_CAP_FILE_WR);
-		spin_unlock(&ci->i_ceph_lock);
-		ceph_put_cap_refs(ci, got);
 
+	/*
+	 * try to do a buffered write.  if we don't have sufficient
+	 * caps, we'll get -EAGAIN from generic_file_aio_write, or a
+	 * short write if we only get caps for some pages.
+	 */
+	if (!(iocb->ki_filp->f_flags & O_DIRECT) &&
+	    !(inode->i_sb->s_flags & MS_SYNCHRONOUS) &&
+	    !(fi->flags & CEPH_F_SYNC)) {
 		ret = generic_file_aio_write(iocb, iov, nr_segs, pos);
+		if (ret >= 0)
+			written = ret;
+
 		if ((ret >= 0 || ret == -EIOCBQUEUED) &&
 		    ((file->f_flags & O_SYNC) || IS_SYNC(file->f_mapping->host)
 		     || ceph_osdmap_flag(osdc->osdmap, CEPH_OSDMAP_NEARFULL))) {
-			err = vfs_fsync_range(file, pos, pos + ret - 1, 1);
+			err = vfs_fsync_range(file, pos, pos + written - 1, 1);
 			if (err < 0)
 				ret = err;
 		}
+		if ((ret < 0 && ret != -EAGAIN) || pos + written >= endoff)
+			goto out;
+	}
 
-		if (dirty)
-			__mark_inode_dirty(inode, dirty);
+	dout("aio_write %p %llx.%llx %llu~%u getting caps. i_size %llu\n",
+	     inode, ceph_vinop(inode), pos + written,
+	     (unsigned)iov->iov_len - written, inode->i_size);
+	ret = ceph_get_caps(ci, CEPH_CAP_FILE_WR, 0, &got, endoff);
+	if (ret < 0)
 		goto out;
-	}
 
+	dout("aio_write %p %llx.%llx %llu~%u  got cap refs on %s\n",
+	     inode, ceph_vinop(inode), pos + written,
+	     (unsigned)iov->iov_len - written, ceph_cap_string(got));
+	ret = ceph_sync_write(file, iov->iov_base + written,
+			      iov->iov_len - written, &iocb->ki_pos);
 	if (ret >= 0) {
 		int dirty;
 		spin_lock(&ci->i_ceph_lock);
@@ -777,13 +767,10 @@ static ssize_t ceph_aio_write(struct kiocb *iocb, const struct iovec *iov,
 		if (dirty)
 			__mark_inode_dirty(inode, dirty);
 	}
-
-out_put:
 	dout("aio_write %p %llx.%llx %llu~%u  dropping cap refs on %s\n",
-	     inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
-	     ceph_cap_string(got));
+	     inode, ceph_vinop(inode), pos + written,
+	     (unsigned)iov->iov_len - written, ceph_cap_string(got));
 	ceph_put_cap_refs(ci, got);
-
 out:
 	if (ret == -EOLDSNAPC) {
 		dout("aio_write %p %llx.%llx %llu~%u got EOLDSNAPC, retrying\n",