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authorDave Chinner <david@fromorbit.com>2016-05-19 00:17:26 +1000
committerAl Viro <viro@zeniv.linux.org.uk>2016-05-18 13:20:21 -0400
commit9f5418010940236b2c39ea53b99055ca26ff1279 (patch)
tree5ef0501c5431567c3c47eb6f2ea1bbfd1311390b /fs
parentfe742fd4f90fa53cf31296bc5131ae1cdd6d84bb (diff)
xfs: concurrent readdir hangs on data buffer locks
There's a three-process deadlock involving shared/exclusive barriers and inverted lock orders in the directory readdir implementation. It's a pre-existing problem with lock ordering, exposed by the VFS parallelisation code. process 1 process 2 process 3 --------- --------- --------- readdir iolock(shared) get_leaf_dents iterate entries ilock(shared) map, lock and read buffer iunlock(shared) process entries in buffer ..... readdir iolock(shared) get_leaf_dents iterate entries ilock(shared) map, lock buffer <blocks> finish ->iterate_shared file_accessed() ->update_time start transaction ilock(excl) <blocks> ..... finishes processing buffer get next buffer ilock(shared) <blocks> And that's the deadlock. Fix this by dropping the current buffer lock in process 1 before trying to map the next buffer. This means we keep the lock order of ilock -> buffer lock intact and hence will allow process 3 to make progress and drop it's ilock(shared) once it is done. Reported-by: Xiong Zhou <xzhou@redhat.com> Signed-off-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
-rw-r--r--fs/xfs/xfs_dir2_readdir.c23
1 files changed, 14 insertions, 9 deletions
diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
index 93b3ab0c5435..f44f79996978 100644
--- a/fs/xfs/xfs_dir2_readdir.c
+++ b/fs/xfs/xfs_dir2_readdir.c
@@ -273,10 +273,11 @@ xfs_dir2_leaf_readbuf(
size_t bufsize,
struct xfs_dir2_leaf_map_info *mip,
xfs_dir2_off_t *curoff,
- struct xfs_buf **bpp)
+ struct xfs_buf **bpp,
+ bool trim_map)
{
struct xfs_inode *dp = args->dp;
- struct xfs_buf *bp = *bpp;
+ struct xfs_buf *bp = NULL;
struct xfs_bmbt_irec *map = mip->map;
struct blk_plug plug;
int error = 0;
@@ -286,13 +287,10 @@ xfs_dir2_leaf_readbuf(
struct xfs_da_geometry *geo = args->geo;
/*
- * If we have a buffer, we need to release it and
- * take it out of the mapping.
+ * If the caller just finished processing a buffer, it will tell us
+ * we need to trim that block out of the mapping now it is done.
*/
-
- if (bp) {
- xfs_trans_brelse(NULL, bp);
- bp = NULL;
+ if (trim_map) {
mip->map_blocks -= geo->fsbcount;
/*
* Loop to get rid of the extents for the
@@ -533,10 +531,17 @@ xfs_dir2_leaf_getdents(
*/
if (!bp || ptr >= (char *)bp->b_addr + geo->blksize) {
int lock_mode;
+ bool trim_map = false;
+
+ if (bp) {
+ xfs_trans_brelse(NULL, bp);
+ bp = NULL;
+ trim_map = true;
+ }
lock_mode = xfs_ilock_data_map_shared(dp);
error = xfs_dir2_leaf_readbuf(args, bufsize, map_info,
- &curoff, &bp);
+ &curoff, &bp, trim_map);
xfs_iunlock(dp, lock_mode);
if (error || !map_info->map_valid)
break;