From a6d8654d885d7d79a3fb82da64eaa489ca332a82 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Tue, 8 Jan 2019 11:44:41 +0000 Subject: Btrfs: fix deadlock when using free space tree due to block group creation When modifying the free space tree we can end up COWing one of its extent buffers which in turn might result in allocating a new chunk, which in turn can result in flushing (finish creation) of pending block groups. If that happens we can deadlock because creating a pending block group needs to update the free space tree, and if any of the updates tries to modify the same extent buffer that we are COWing, we end up in a deadlock since we try to write lock twice the same extent buffer. So fix this by skipping pending block group creation if we are COWing an extent buffer from the free space tree. This is a case missed by commit 5ce555578e091 ("Btrfs: fix deadlock when writing out free space caches"). Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=202173 Fixes: 5ce555578e091 ("Btrfs: fix deadlock when writing out free space caches") CC: stable@vger.kernel.org # 4.18+ Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/ctree.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index d92462fe66c82..f64aad6137276 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -1016,19 +1016,21 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans, parent_start = parent->start; /* - * If we are COWing a node/leaf from the extent, chunk or device trees, - * make sure that we do not finish block group creation of pending block - * groups. We do this to avoid a deadlock. + * If we are COWing a node/leaf from the extent, chunk, device or free + * space trees, make sure that we do not finish block group creation of + * pending block groups. We do this to avoid a deadlock. * COWing can result in allocation of a new chunk, and flushing pending * block groups (btrfs_create_pending_block_groups()) can be triggered * when finishing allocation of a new chunk. Creation of a pending block - * group modifies the extent, chunk and device trees, therefore we could - * deadlock with ourselves since we are holding a lock on an extent - * buffer that btrfs_create_pending_block_groups() may try to COW later. + * group modifies the extent, chunk, device and free space trees, + * therefore we could deadlock with ourselves since we are holding a + * lock on an extent buffer that btrfs_create_pending_block_groups() may + * try to COW later. */ if (root == fs_info->extent_root || root == fs_info->chunk_root || - root == fs_info->dev_root) + root == fs_info->dev_root || + root == fs_info->free_space_root) trans->can_flush_pending_bgs = false; cow = btrfs_alloc_tree_block(trans, root, parent_start, -- cgit v1.2.3