diff options
| author | Dave Chinner <david@fromorbit.com> | 2016-05-19 00:17:26 +1000 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2016-05-18 13:20:21 -0400 |
| commit | 9f5418010940236b2c39ea53b99055ca26ff1279 (patch) | |
| tree | 5ef0501c5431567c3c47eb6f2ea1bbfd1311390b /fs/xfs | |
| parent | fe742fd4f90fa53cf31296bc5131ae1cdd6d84bb (diff) | |
| download | linux-9f5418010940236b2c39ea53b99055ca26ff1279.tar.bz2 | |
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/xfs')
| -rw-r--r-- | fs/xfs/xfs_dir2_readdir.c | 23 |
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; |