Currently the generation field of struct btrfs_fs_info is always modified
while holding fs_info->trans_lock locked. Most readers will access this
field without taking that lock but while holding a transaction handle,
which is safe to do due to the transaction life cycle.
However there are other readers that are neither holding the lock nor
holding a transaction handle open:
1) When reading an inode from disk, at btrfs_read_locked_inode();
2) When reading the generation to expose it to sysfs, at
btrfs_generation_show();
3) Early in the fsync path, at skip_inode_logging();
4) When creating a hole at btrfs_cont_expand(), during write paths,
truncate and reflinking;
5) In the fs_info ioctl (btrfs_ioctl_fs_info());
6) While mounting the filesystem, in the open_ctree() path. In these
cases it's safe to directly read fs_info->generation as no one
can concurrently start a transaction and update fs_info->generation.
In case of the fsync path, races here should be harmless, and in the worst
case they may cause a fsync to log an inode when it's not really needed,
so nothing bad from a functional perspective. In the other cases it's not
so clear if functional problems may arise, though in case 1 rare things
like a load/store tearing [1] may cause the BTRFS_INODE_NEEDS_FULL_SYNC
flag not being set on an inode and therefore result in incorrect logging
later on in case a fsync call is made.
To avoid data race warnings from tools like KCSAN and other issues such
as load and store tearing (amongst others, see [1]), create helpers to
access the generation field of struct btrfs_fs_info using READ_ONCE() and
WRITE_ONCE(), and use these helpers where needed.
[1] https://lwn.net/Articles/793253/
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
struct btrfs_inode *inode = BTRFS_I(ctx->inode);
struct btrfs_fs_info *fs_info = inode->root->fs_info;
struct btrfs_inode *inode = BTRFS_I(ctx->inode);
struct btrfs_fs_info *fs_info = inode->root->fs_info;
- if (btrfs_inode_in_log(inode, fs_info->generation) &&
+ if (btrfs_inode_in_log(inode, btrfs_get_fs_generation(fs_info)) &&
list_empty(&ctx->ordered_extents))
return true;
list_empty(&ctx->ordered_extents))
return true;
struct btrfs_block_rsv empty_block_rsv;
struct btrfs_block_rsv empty_block_rsv;
+ /*
+ * Updated while holding the lock 'trans_lock'. Due to the life cycle of
+ * a transaction, it can be directly read while holding a transaction
+ * handle, everywhere else must be read with btrfs_get_fs_generation().
+ * Should always be updated using btrfs_set_fs_generation().
+ */
u64 generation;
u64 last_trans_committed;
/*
u64 generation;
u64 last_trans_committed;
/*
+static inline u64 btrfs_get_fs_generation(const struct btrfs_fs_info *fs_info)
+{
+ return READ_ONCE(fs_info->generation);
+}
+
+static inline void btrfs_set_fs_generation(struct btrfs_fs_info *fs_info, u64 gen)
+{
+ WRITE_ONCE(fs_info->generation, gen);
+}
+
static inline void btrfs_set_last_root_drop_gen(struct btrfs_fs_info *fs_info,
u64 gen)
{
static inline void btrfs_set_last_root_drop_gen(struct btrfs_fs_info *fs_info,
u64 gen)
{
* This is required for both inode re-read from disk and delayed inode
* in delayed_nodes_tree.
*/
* This is required for both inode re-read from disk and delayed inode
* in delayed_nodes_tree.
*/
- if (BTRFS_I(inode)->last_trans == fs_info->generation)
+ if (BTRFS_I(inode)->last_trans == btrfs_get_fs_generation(fs_info))
set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
&BTRFS_I(inode)->runtime_flags);
set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
&BTRFS_I(inode)->runtime_flags);
hole_em->orig_block_len = 0;
hole_em->ram_bytes = hole_size;
hole_em->compress_type = BTRFS_COMPRESS_NONE;
hole_em->orig_block_len = 0;
hole_em->ram_bytes = hole_size;
hole_em->compress_type = BTRFS_COMPRESS_NONE;
- hole_em->generation = fs_info->generation;
+ hole_em->generation = btrfs_get_fs_generation(fs_info);
err = btrfs_replace_extent_map_range(inode, hole_em, true);
free_extent_map(hole_em);
err = btrfs_replace_extent_map_range(inode, hole_em, true);
free_extent_map(hole_em);
}
if (flags_in & BTRFS_FS_INFO_FLAG_GENERATION) {
}
if (flags_in & BTRFS_FS_INFO_FLAG_GENERATION) {
- fi_args->generation = fs_info->generation;
+ fi_args->generation = btrfs_get_fs_generation(fs_info);
fi_args->flags |= BTRFS_FS_INFO_FLAG_GENERATION;
}
fi_args->flags |= BTRFS_FS_INFO_FLAG_GENERATION;
}
{
struct btrfs_fs_info *fs_info = to_fs_info(kobj);
{
struct btrfs_fs_info *fs_info = to_fs_info(kobj);
- return sysfs_emit(buf, "%llu\n", fs_info->generation);
+ return sysfs_emit(buf, "%llu\n", btrfs_get_fs_generation(fs_info));
}
BTRFS_ATTR(, generation, btrfs_generation_show);
}
BTRFS_ATTR(, generation, btrfs_generation_show);
IO_TREE_TRANS_DIRTY_PAGES);
extent_io_tree_init(fs_info, &cur_trans->pinned_extents,
IO_TREE_FS_PINNED_EXTENTS);
IO_TREE_TRANS_DIRTY_PAGES);
extent_io_tree_init(fs_info, &cur_trans->pinned_extents,
IO_TREE_FS_PINNED_EXTENTS);
+ btrfs_set_fs_generation(fs_info, fs_info->generation + 1);
cur_trans->transid = fs_info->generation;
fs_info->running_transaction = cur_trans;
cur_trans->aborted = 0;
cur_trans->transid = fs_info->generation;
fs_info->running_transaction = cur_trans;
cur_trans->aborted = 0;