From 956d21c81b53790b481e083a7f4ba58f29b6a467 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Tue, 19 Nov 2019 13:59:35 -0500 Subject: [PATCH] btrfs: do not call synchronize_srcu() in inode_tree_del [ Upstream commit f72ff01df9cf5db25c76674cac16605992d15467 ] Testing with the new fsstress uncovered a pretty nasty deadlock with lookup and snapshot deletion. Process A unlink -> final iput -> inode_tree_del -> synchronize_srcu(subvol_srcu) Process B btrfs_lookup <- srcu_read_lock() acquired here -> btrfs_iget -> find inode that has I_FREEING set -> __wait_on_freeing_inode() We're holding the srcu_read_lock() while doing the iget in order to make sure our fs root doesn't go away, and then we are waiting for the inode to finish freeing. However because the free'ing process is doing a synchronize_srcu() we deadlock. Fix this by dropping the synchronize_srcu() in inode_tree_del(). We don't need people to stop accessing the fs root at this point, we're only adding our empty root to the dead roots list. A larger much more invasive fix is forthcoming to address how we deal with fs roots, but this fixes the immediate problem. Fixes: 76dda93c6ae2 ("Btrfs: add snapshot/subvolume destroy ioctl") CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/inode.c | 1 - 1 file changed, 1 deletion(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 383717cce..548e9cd1a 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5506,7 +5506,6 @@ static void inode_tree_del(struct inode *inode) spin_unlock(&root->inode_lock); if (empty && btrfs_root_refs(&root->root_item) == 0) { - synchronize_srcu(&root->fs_info->subvol_srcu); spin_lock(&root->inode_lock); empty = RB_EMPTY_ROOT(&root->inode_tree); spin_unlock(&root->inode_lock);