[Ocfs2-devel] [PATCH v3] ocfs2: the ip_alloc_sem should be taken in ocfs2_get_block()

[alex chen]

The ip_alloc_sem should be taken in ocfs2_get_block() when reading file
in DIRECT mode to prevent concurrent access to extent tree with
ocfs2_dio_end_io_write(), which may cause BUGON in the following situation:

read file 'A'                                  end_io of writing file 'A'
vfs_read
 __vfs_read
  ocfs2_file_read_iter
   generic_file_read_iter
    ocfs2_direct_IO
     __blockdev_direct_IO
      do_blockdev_direct_IO
       do_direct_IO
        get_more_blocks
         ocfs2_get_block
          ocfs2_extent_map_get_blocks
           ocfs2_get_clusters
            ocfs2_get_clusters_nocache()
             ocfs2_search_extent_list
              return the index of record which
              contains the v_cluster, that is
              v_cluster > rec[i]->e_cpos.
                                                ocfs2_dio_end_io
                                                 ocfs2_dio_end_io_write
                                                  down_write(&oi->ip_alloc_sem);
                                                  ocfs2_mark_extent_written
                                                   ocfs2_change_extent_flag
                                                    ocfs2_split_extent
                                                     ...
                                                 --> modify the rec[i]->e_cpos, resulting
                                                     in v_cluster < rec[i]->e_cpos.
             BUG_ON(v_cluster < le32_to_cpu(rec->e_cpos))

Fixes: c15471f79506 ("ocfs2: fix sparse file & data ordering issue in direct io")

Signed-off-by: Alex Chen <alex.chen at huawei.com>
Reviewed-by: Jun Piao <piaojun at huawei.com>
Acked-by: Changwei Ge <ge.changwei at h3c.com>

---
 fs/ocfs2/aops.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index 88a31e9..d151632 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -134,6 +134,19 @@ static int ocfs2_symlink_get_block(struct inode *inode, sector_t iblock,
 	return err;
 }

+static int ocfs2_lock_get_block(struct inode *inode, sector_t iblock,
+		    struct buffer_head *bh_result, int create)
+{
+	int ret = 0;
+	struct ocfs2_inode_info *oi = OCFS2_I(inode);
+
+	down_read(&oi->ip_alloc_sem);
+	ret = ocfs2_get_block(inode, iblock, bh_result, create);
+	up_read(&oi->ip_alloc_sem);
+
+	return ret;
+}
+
 int ocfs2_get_block(struct inode *inode, sector_t iblock,
 		    struct buffer_head *bh_result, int create)
 {
@@ -2128,7 +2141,7 @@ static void ocfs2_dio_free_write_ctx(struct inode *inode,
  * called like this: dio->get_blocks(dio->inode, fs_startblk,
  * 					fs_count, map_bh, dio->rw == WRITE);
  */
-static int ocfs2_dio_get_block(struct inode *inode, sector_t iblock,
+static int ocfs2_dio_wr_get_block(struct inode *inode, sector_t iblock,
 			       struct buffer_head *bh_result, int create)
 {
 	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
@@ -2154,12 +2167,9 @@ static int ocfs2_dio_get_block(struct inode *inode, sector_t iblock,
 	 * while file size will be changed.
 	 */
 	if (pos + total_len <= i_size_read(inode)) {
-		down_read(&oi->ip_alloc_sem);
-		/* This is the fast path for re-write. */
-		ret = ocfs2_get_block(inode, iblock, bh_result, create);
-
-		up_read(&oi->ip_alloc_sem);

+		/* This is the fast path for re-write. */
+		ret = ocfs2_lock_get_block(inode, iblock, bh_result, create);
 		if (buffer_mapped(bh_result) &&
 		    !buffer_new(bh_result) &&
 		    ret == 0)
@@ -2424,9 +2434,9 @@ static ssize_t ocfs2_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 		return 0;

 	if (iov_iter_rw(iter) == READ)
-		get_block = ocfs2_get_block;
+		get_block = ocfs2_lock_get_block;
 	else
-		get_block = ocfs2_dio_get_block;
+		get_block = ocfs2_dio_wr_get_block;

 	return __blockdev_direct_IO(iocb, inode, inode->i_sb->s_bdev,
 				    iter, get_block,
-- 
1.9.5.msysgit.1