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(-) (limited to 'fs/btrfs/ctree.c') diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index d92462fe66c8..f64aad613727 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 From a6279470762c19ba97e454f90798373dccdf6148 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Fri, 25 Jan 2019 11:48:51 +0000 Subject: Btrfs: fix deadlock when allocating tree block during leaf/node split When splitting a leaf or node from one of the trees that are modified when flushing pending block groups (extent, chunk, device and free space trees), we need to allocate a new tree block, which in turn can result in the need to allocate a new block group. After allocating the new block group we may need to flush new block groups that were previously allocated during the course of the current transaction, which is what may cause a deadlock due to attempts to write lock twice the same leaf or node, as when splitting a leaf or node we are holding a write lock on it and its parent node. The same type of deadlock can also happen when increasing the tree's height, since we are holding a lock on the existing root while allocating the tree block to use as the new root node. An example trace when the deadlock happens during the leaf split path is: [27175.293054] CPU: 0 PID: 3005 Comm: kworker/u17:6 Tainted: G W 4.19.16 #1 [27175.293942] Hardware name: Penguin Computing Relion 1900/MD90-FS0-ZB-XX, BIOS R15 06/25/2018 [27175.294846] Workqueue: btrfs-extent-refs btrfs_extent_refs_helper [btrfs] (...) [27175.298384] RSP: 0018:ffffab2087107758 EFLAGS: 00010246 [27175.299269] RAX: 0000000000000bbd RBX: ffff9fadc7141c48 RCX: 0000000000000001 [27175.300155] RDX: 0000000000000001 RSI: 0000000000000002 RDI: ffff9fadc7141c48 [27175.301023] RBP: 0000000000000001 R08: ffff9faeb6ac1040 R09: ffff9fa9c0000000 [27175.301887] R10: 0000000000000000 R11: 0000000000000040 R12: ffff9fb21aac8000 [27175.302743] R13: ffff9fb1a64d6a20 R14: 0000000000000001 R15: ffff9fb1a64d6a18 [27175.303601] FS: 0000000000000000(0000) GS:ffff9fb21fa00000(0000) knlGS:0000000000000000 [27175.304468] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [27175.305339] CR2: 00007fdc8743ead8 CR3: 0000000763e0a006 CR4: 00000000003606f0 [27175.306220] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [27175.307087] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [27175.307940] Call Trace: [27175.308802] btrfs_search_slot+0x779/0x9a0 [btrfs] [27175.309669] ? update_space_info+0xba/0xe0 [btrfs] [27175.310534] btrfs_insert_empty_items+0x67/0xc0 [btrfs] [27175.311397] btrfs_insert_item+0x60/0xd0 [btrfs] [27175.312253] btrfs_create_pending_block_groups+0xee/0x210 [btrfs] [27175.313116] do_chunk_alloc+0x25f/0x300 [btrfs] [27175.313984] find_free_extent+0x706/0x10d0 [btrfs] [27175.314855] btrfs_reserve_extent+0x9b/0x1d0 [btrfs] [27175.315707] btrfs_alloc_tree_block+0x100/0x5b0 [btrfs] [27175.316548] split_leaf+0x130/0x610 [btrfs] [27175.317390] btrfs_search_slot+0x94d/0x9a0 [btrfs] [27175.318235] btrfs_insert_empty_items+0x67/0xc0 [btrfs] [27175.319087] alloc_reserved_file_extent+0x84/0x2c0 [btrfs] [27175.319938] __btrfs_run_delayed_refs+0x596/0x1150 [btrfs] [27175.320792] btrfs_run_delayed_refs+0xed/0x1b0 [btrfs] [27175.321643] delayed_ref_async_start+0x81/0x90 [btrfs] [27175.322491] normal_work_helper+0xd0/0x320 [btrfs] [27175.323328] ? move_linked_works+0x6e/0xa0 [27175.324160] process_one_work+0x191/0x370 [27175.324976] worker_thread+0x4f/0x3b0 [27175.325763] kthread+0xf8/0x130 [27175.326531] ? rescuer_thread+0x320/0x320 [27175.327284] ? kthread_create_worker_on_cpu+0x50/0x50 [27175.328027] ret_from_fork+0x35/0x40 [27175.328741] ---[ end trace 300a1b9f0ac30e26 ]--- Fix this by preventing the flushing of new blocks groups when splitting a leaf/node and when inserting a new root node for one of the trees modified by the flushing operation, similar to what is done when COWing a node/leaf from on of these trees. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=202383 Reported-by: Eli V CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- fs/btrfs/ctree.c | 78 ++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 50 insertions(+), 28 deletions(-) (limited to 'fs/btrfs/ctree.c') diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index f64aad613727..5a6c39b44c84 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -968,6 +968,48 @@ static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans, return 0; } +static struct extent_buffer *alloc_tree_block_no_bg_flush( + struct btrfs_trans_handle *trans, + struct btrfs_root *root, + u64 parent_start, + const struct btrfs_disk_key *disk_key, + int level, + u64 hint, + u64 empty_size) +{ + struct btrfs_fs_info *fs_info = root->fs_info; + struct extent_buffer *ret; + + /* + * 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, 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. + * For similar reasons, we also need to delay flushing pending block + * groups when splitting a leaf or node, from one of those trees, since + * we are holding a write lock on it and its parent or when inserting a + * new root node for one of those trees. + */ + if (root == fs_info->extent_root || + root == fs_info->chunk_root || + root == fs_info->dev_root || + root == fs_info->free_space_root) + trans->can_flush_pending_bgs = false; + + ret = btrfs_alloc_tree_block(trans, root, parent_start, + root->root_key.objectid, disk_key, level, + hint, empty_size); + trans->can_flush_pending_bgs = true; + + return ret; +} + /* * does the dirty work in cow of a single block. The parent block (if * supplied) is updated to point to the new cow copy. The new buffer is marked @@ -1015,28 +1057,8 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans, if ((root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) && parent) parent_start = parent->start; - /* - * 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, 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->free_space_root) - trans->can_flush_pending_bgs = false; - - cow = btrfs_alloc_tree_block(trans, root, parent_start, - root->root_key.objectid, &disk_key, level, - search_start, empty_size); - trans->can_flush_pending_bgs = true; + cow = alloc_tree_block_no_bg_flush(trans, root, parent_start, &disk_key, + level, search_start, empty_size); if (IS_ERR(cow)) return PTR_ERR(cow); @@ -3345,8 +3367,8 @@ static noinline int insert_new_root(struct btrfs_trans_handle *trans, else btrfs_node_key(lower, &lower_key, 0); - c = btrfs_alloc_tree_block(trans, root, 0, root->root_key.objectid, - &lower_key, level, root->node->start, 0); + c = alloc_tree_block_no_bg_flush(trans, root, 0, &lower_key, level, + root->node->start, 0); if (IS_ERR(c)) return PTR_ERR(c); @@ -3475,8 +3497,8 @@ static noinline int split_node(struct btrfs_trans_handle *trans, mid = (c_nritems + 1) / 2; btrfs_node_key(c, &disk_key, mid); - split = btrfs_alloc_tree_block(trans, root, 0, root->root_key.objectid, - &disk_key, level, c->start, 0); + split = alloc_tree_block_no_bg_flush(trans, root, 0, &disk_key, level, + c->start, 0); if (IS_ERR(split)) return PTR_ERR(split); @@ -4260,8 +4282,8 @@ again: else btrfs_item_key(l, &disk_key, mid); - right = btrfs_alloc_tree_block(trans, root, 0, root->root_key.objectid, - &disk_key, 0, l->start, 0); + right = alloc_tree_block_no_bg_flush(trans, root, 0, &disk_key, 0, + l->start, 0); if (IS_ERR(right)) return PTR_ERR(right); -- cgit v1.2.3