From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:62791 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752846AbaKZQPu (ORCPT ); Wed, 26 Nov 2014 11:15:50 -0500 Message-ID: <5475FCB0.4090608@fb.com> Date: Wed, 26 Nov 2014 11:15:44 -0500 From: Josef Bacik MIME-Version: 1.0 To: Filipe Manana , Subject: Re: [PATCH 4/6] Btrfs: fix race between fs trimming and block group remove/allocation References: <1417015735-8581-1-git-send-email-fdmanana@suse.com> <1417015735-8581-5-git-send-email-fdmanana@suse.com> In-Reply-To: <1417015735-8581-5-git-send-email-fdmanana@suse.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 11/26/2014 10:28 AM, Filipe Manana wrote: > Our fs trim operation, which is completely transactionless (doesn't start > or joins an existing transaction) consists of visiting all block groups > and then for each one to iterate its free space entries and perform a > discard operation against the space range represented by the free space > entries. However before performing a discard, the corresponding free space > entry is removed from the free space rbtree, and when the discard completes > it is added back to the free space rbtree. > > If a block group remove operation happens while the discard is ongoing (or > before it starts and after a free space entry is hidden), we end up not > waiting for the discard to complete, remove the extent map that maps > logical address to physical addresses and the corresponding chunk metadata > from the the chunk and device trees. After that and before the discard > completes, the current running transaction can finish and a new one start, > allowing for new block groups that map to the same physical addresses to > be allocated and written to. > > So fix this by keeping the extent map in memory until the discard completes > so that the same physical addresses aren't reused before it completes. > > If the physical locations that are under a discard operation end up being > used for a new metadata block group for example, and dirty metadata extents > are written before the discard finishes (the VM might call writepages() of > our btree inode's i_mapping for example, or an fsync log commit happens) we > end up overwriting metadata with zeroes, which leads to errors from fsck > like the following: > > checking extents > Check tree block failed, want=833912832, have=0 > Check tree block failed, want=833912832, have=0 > Check tree block failed, want=833912832, have=0 > Check tree block failed, want=833912832, have=0 > Check tree block failed, want=833912832, have=0 > read block failed check_tree_block > owner ref check failed [833912832 16384] > Errors found in extent allocation tree or chunk allocation > checking free space cache > checking fs roots > Check tree block failed, want=833912832, have=0 > Check tree block failed, want=833912832, have=0 > Check tree block failed, want=833912832, have=0 > Check tree block failed, want=833912832, have=0 > Check tree block failed, want=833912832, have=0 > read block failed check_tree_block > root 5 root dir 256 error > root 5 inode 260 errors 2001, no inode item, link count wrong > unresolved ref dir 256 index 0 namelen 8 name foobar_3 filetype 1 errors 6, no dir index, no inode ref > root 5 inode 262 errors 2001, no inode item, link count wrong > unresolved ref dir 256 index 0 namelen 8 name foobar_5 filetype 1 errors 6, no dir index, no inode ref > root 5 inode 263 errors 2001, no inode item, link count wrong > (...) > > Signed-off-by: Filipe Manana > --- > fs/btrfs/ctree.h | 13 ++++++++++++- > fs/btrfs/disk-io.c | 14 ++++++++++++++ > fs/btrfs/extent-tree.c | 24 +++++++++++++++++++++++- > fs/btrfs/free-space-cache.c | 26 +++++++++++++++++++++++++- > fs/btrfs/volumes.c | 33 ++++++++++++++++++++++++++------- > 5 files changed, 100 insertions(+), 10 deletions(-) > > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h > index 7f40a65..51056c7 100644 > --- a/fs/btrfs/ctree.h > +++ b/fs/btrfs/ctree.h > @@ -1278,6 +1278,7 @@ struct btrfs_block_group_cache { > unsigned int dirty:1; > unsigned int iref:1; > unsigned int has_caching_ctl:1; > + unsigned int removed:1; > > int disk_cache_state; > > @@ -1307,6 +1308,8 @@ struct btrfs_block_group_cache { > > /* For delayed block group creation or deletion of empty block groups */ > struct list_head bg_list; > + > + atomic_t trimming; > }; > > /* delayed seq elem */ > @@ -1731,6 +1734,13 @@ struct btrfs_fs_info { > > /* For btrfs to record security options */ > struct security_mnt_opts security_opts; > + > + /* > + * Chunks that can't be freed yet (under a trim/discard operation) > + * and will be latter freed. > + */ > + rwlock_t pinned_chunks_lock; > + struct list_head pinned_chunks; > }; > > struct btrfs_subvolume_writers { > @@ -3353,7 +3363,8 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans, > u64 type, u64 chunk_objectid, u64 chunk_offset, > u64 size); > int btrfs_remove_block_group(struct btrfs_trans_handle *trans, > - struct btrfs_root *root, u64 group_start); > + struct btrfs_root *root, u64 group_start, > + bool *remove_em); > void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info); > void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans, > struct btrfs_root *root); > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index 9d4fb0a..76012d0 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -2397,6 +2397,9 @@ int open_ctree(struct super_block *sb, > init_waitqueue_head(&fs_info->transaction_blocked_wait); > init_waitqueue_head(&fs_info->async_submit_wait); > > + rwlock_init(&fs_info->pinned_chunks_lock); > + INIT_LIST_HEAD(&fs_info->pinned_chunks); > + > ret = btrfs_alloc_stripe_hash_table(fs_info); > if (ret) { > err = ret; > @@ -3726,6 +3729,17 @@ void close_ctree(struct btrfs_root *root) > > btrfs_free_block_rsv(root, root->orphan_block_rsv); > root->orphan_block_rsv = NULL; > + > + write_lock(&fs_info->pinned_chunks_lock); > + while (!list_empty(&fs_info->pinned_chunks)) { > + struct extent_map *em; > + > + em = list_first_entry(&fs_info->pinned_chunks, > + struct extent_map, list); > + list_del_init(&em->list); > + free_extent_map(em); > + } > + write_unlock(&fs_info->pinned_chunks_lock); > } > > int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid, > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index 92f61f2..4bf8f02 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -9016,6 +9016,7 @@ btrfs_create_block_group_cache(struct btrfs_root *root, u64 start, u64 size) > INIT_LIST_HEAD(&cache->cluster_list); > INIT_LIST_HEAD(&cache->bg_list); > btrfs_init_free_space_ctl(cache); > + atomic_set(&cache->trimming, 0); > > return cache; > } > @@ -9317,7 +9318,8 @@ static void clear_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags) > } > > int btrfs_remove_block_group(struct btrfs_trans_handle *trans, > - struct btrfs_root *root, u64 group_start) > + struct btrfs_root *root, u64 group_start, > + bool *remove_em) > { > struct btrfs_path *path; > struct btrfs_block_group_cache *block_group; > @@ -9474,6 +9476,26 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans, > > memcpy(&key, &block_group->key, sizeof(key)); > > + spin_lock(&block_group->lock); > + block_group->removed = 1; Ok you set block_group->removed here, but you don't check it in btrfs_trim_block_group, so we can easily race in afterwards and start trimming this block group. > + /* > + * At this point trimming can't start on this block group, because we > + * removed the block group from the tree fs_info->block_group_cache_tree > + * so no one can't find it anymore. > + * > + * And we must tell our caller to not remove the extent map from the > + * fs_info->mapping_tree to prevent the same logical address range and > + * physical device space ranges from being reused for a new block group. > + * This is because our fs trim operation (btrfs_trim_fs(), > + * btrfs_ioctl_fitrim()) is completely transactionless, so while its > + * trimming a range the currently running transaction might finish and > + * a new one start, allowing for new block groups to be created that can > + * reuse the same physical device locations unless we take this special > + * care. > + */ > + *remove_em = (atomic_read(&block_group->trimming) == 0); > + spin_unlock(&block_group->lock); > + > btrfs_put_block_group(block_group); > btrfs_put_block_group(block_group); > > diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c > index 3384819..16c2d39 100644 > --- a/fs/btrfs/free-space-cache.c > +++ b/fs/btrfs/free-space-cache.c > @@ -3101,11 +3101,35 @@ int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group, > > *trimmed = 0; > > + atomic_inc(&block_group->trimming); > + This needs to be something like this spin_lock(&block_group->lock); if (block_group->removed == 1) { spin_unlock(&block_group->lock); return 0; } atomic_inc(&block_group->trimming); spin_unlock(&block_group->lock); To be properly safe. Thanks, Josef