From fe742fd4f90fa53cf31296bc5131ae1cdd6d84bb Mon Sep 17 00:00:00 2001 From: Al Viro Date: Wed, 18 May 2016 13:15:05 -0400 Subject: [PATCH 1/2] Revert "btrfs: switch to ->iterate_shared()" This reverts commit 972b241f8441dc37a3f89dcd7e71d7f013873d13. Quoth Chris: didn't take the delayed inode stuff into account it got an rbtree of items and it pulls things out so in shared mode, its hugely racey sorry, lets revert and fix it for real inside of btrfs Signed-off-by: Chris Mason Signed-off-by: Al Viro --- fs/btrfs/inode.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 3e2ada1267f3..2aaba58b4856 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -10181,7 +10181,7 @@ static const struct inode_operations btrfs_dir_ro_inode_operations = { static const struct file_operations btrfs_dir_file_operations = { .llseek = generic_file_llseek, .read = generic_read_dir, - .iterate_shared = btrfs_real_readdir, + .iterate = btrfs_real_readdir, .unlocked_ioctl = btrfs_ioctl, #ifdef CONFIG_COMPAT .compat_ioctl = btrfs_ioctl, From 9f5418010940236b2c39ea53b99055ca26ff1279 Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Thu, 19 May 2016 00:17:26 +1000 Subject: [PATCH 2/2] 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 finish ->iterate_shared file_accessed() ->update_time start transaction ilock(excl) ..... finishes processing buffer get next buffer ilock(shared) 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 Signed-off-by: Dave Chinner Signed-off-by: Al Viro --- fs/xfs/xfs_dir2_readdir.c | 23 ++++++++++++++--------- 1 file 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;