6.16-stable review patch. If anyone has any objections, please let me know.
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From: Filipe Manana fdmanana@suse.com
[ Upstream commit 59a0dd4ab98970086fd096281b1606c506ff2698 ]
At inode_logged() if we find that the inode was not logged before we update its ->last_dir_index_offset to (u64)-1 with the goal that the next directory log operation will see the (u64)-1 and then figure out it must check what was the index of the last logged dir index key and update ->last_dir_index_offset to that key's offset (this is done in update_last_dir_index_offset()).
This however has a possibility for a time window where a race can happen and lead to directory logging skipping dir index keys that should be logged. The race happens like this:
1) Task A calls inode_logged(), sees ->logged_trans as 0 and then checks that the inode item was logged before, but before it sets the inode's ->last_dir_index_offset to (u64)-1...
2) Task B is at btrfs_log_inode() which calls inode_logged() early, and that has set ->last_dir_index_offset to (u64)-1;
3) Task B then enters log_directory_changes() which calls update_last_dir_index_offset(). There it sees ->last_dir_index_offset is (u64)-1 and that the inode was logged before (ctx->logged_before is true), and so it searches for the last logged dir index key in the log tree and it finds that it has an offset (index) value of N, so it sets ->last_dir_index_offset to N, so that we can skip index keys that are less than or equal to N (later at process_dir_items_leaf());
4) Task A now sets ->last_dir_index_offset to (u64)-1, undoing the update that task B just did;
5) Task B will now skip every index key when it enters process_dir_items_leaf(), since ->last_dir_index_offset is (u64)-1.
Fix this by making inode_logged() not touch ->last_dir_index_offset and initializing it to 0 when an inode is loaded (at btrfs_alloc_inode()) and then having update_last_dir_index_offset() treat a value of 0 as meaning we must check the log tree and update with the index of the last logged index key. This is fine since the minimum possible value for ->last_dir_index_offset is 1 (BTRFS_DIR_START_INDEX - 1 = 2 - 1 = 1). This also simplifies the management of ->last_dir_index_offset and now all accesses to it are done under the inode's log_mutex.
Fixes: 0f8ce49821de ("btrfs: avoid inode logging during rename and link when possible") Reviewed-by: Boris Burkov boris@bur.io Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/btrfs_inode.h | 2 +- fs/btrfs/inode.c | 1 + fs/btrfs/tree-log.c | 17 ++--------------- 3 files changed, 4 insertions(+), 16 deletions(-)
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h index a79fa0726f1d9..216eff293ffec 100644 --- a/fs/btrfs/btrfs_inode.h +++ b/fs/btrfs/btrfs_inode.h @@ -248,7 +248,7 @@ struct btrfs_inode { u64 new_delalloc_bytes; /* * The offset of the last dir index key that was logged. - * This is used only for directories. + * This is used only for directories. Protected by 'log_mutex'. */ u64 last_dir_index_offset; }; diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index df4c8312aae39..ffa5d6c159405 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -7827,6 +7827,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb) ei->last_sub_trans = 0; ei->logged_trans = 0; ei->delalloc_bytes = 0; + /* new_delalloc_bytes and last_dir_index_offset are in a union. */ ei->new_delalloc_bytes = 0; ei->defrag_bytes = 0; ei->disk_i_size = 0; diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 17003f3d9dd1c..5f82e8c59cd17 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -3435,19 +3435,6 @@ static int inode_logged(const struct btrfs_trans_handle *trans, inode->logged_trans = trans->transid; spin_unlock(&inode->lock);
- /* - * If it's a directory, then we must set last_dir_index_offset to the - * maximum possible value, so that the next attempt to log the inode does - * not skip checking if dir index keys found in modified subvolume tree - * leaves have been logged before, otherwise it would result in attempts - * to insert duplicate dir index keys in the log tree. This must be done - * because last_dir_index_offset is an in-memory only field, not persisted - * in the inode item or any other on-disk structure, so its value is lost - * once the inode is evicted. - */ - if (S_ISDIR(inode->vfs_inode.i_mode)) - inode->last_dir_index_offset = (u64)-1; - return 1; }
@@ -4038,7 +4025,7 @@ static noinline int log_dir_items(struct btrfs_trans_handle *trans,
/* * If the inode was logged before and it was evicted, then its - * last_dir_index_offset is (u64)-1, so we don't the value of the last index + * last_dir_index_offset is 0, so we don't know the value of the last index * key offset. If that's the case, search for it and update the inode. This * is to avoid lookups in the log tree every time we try to insert a dir index * key from a leaf changed in the current transaction, and to allow us to always @@ -4054,7 +4041,7 @@ static int update_last_dir_index_offset(struct btrfs_inode *inode,
lockdep_assert_held(&inode->log_mutex);
- if (inode->last_dir_index_offset != (u64)-1) + if (inode->last_dir_index_offset != 0) return 0;
if (!ctx->logged_before) {