From: Filipe Manana Date: Wed, 4 Oct 2023 10:38:50 +0000 (+0100) Subject: btrfs: add and use helpers for reading and writing fs_info->generation X-Git-Tag: v6.7-rc1~202^2~11 X-Git-Url: http://git.ipfire.org/?p=thirdparty%2Flinux.git;a=commitdiff_plain;h=4a4f8fe2b0230c22aba40c9f8ea7b9c6fcfc8417 btrfs: add and use helpers for reading and writing fs_info->generation 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 Reviewed-by: David Sterba Signed-off-by: David Sterba --- diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 004c53482f05f..723f0c70452e5 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1749,7 +1749,7 @@ static inline bool skip_inode_logging(const struct btrfs_log_ctx *ctx) 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; diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h index 2bd9bedc70958..d04b729cbdf33 100644 --- a/fs/btrfs/fs.h +++ b/fs/btrfs/fs.h @@ -416,6 +416,12 @@ struct btrfs_fs_info { 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; /* @@ -817,6 +823,16 @@ struct btrfs_fs_info { #endif }; +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) { diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 3b3aec302c33c..c9317c047587f 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -3800,7 +3800,7 @@ cache_index: * 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); @@ -4923,7 +4923,7 @@ int btrfs_cont_expand(struct btrfs_inode *inode, loff_t oldsize, loff_t size) 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); diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 848b7e6f6421b..7ab21283fae80 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -2822,7 +2822,7 @@ static long btrfs_ioctl_fs_info(struct btrfs_fs_info *fs_info, } 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; } diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c index e07be193323a3..21ab8b9b62ce1 100644 --- a/fs/btrfs/sysfs.c +++ b/fs/btrfs/sysfs.c @@ -1201,7 +1201,7 @@ static ssize_t btrfs_generation_show(struct kobject *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); diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 3aa59cfa4ab01..f5db3a483f405 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -386,7 +386,7 @@ loop: IO_TREE_TRANS_DIRTY_PAGES); extent_io_tree_init(fs_info, &cur_trans->pinned_extents, IO_TREE_FS_PINNED_EXTENTS); - fs_info->generation++; + 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;