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authorFilipe Manana <fdmanana@suse.com>2023-10-04 13:38:50 +0300
committerDavid Sterba <dsterba@suse.com>2023-10-12 17:44:17 +0300
commit4a4f8fe2b0230c22aba40c9f8ea7b9c6fcfc8417 (patch)
treef176f27ed820f8af1d5abaada190b0cc954c3152 /fs/btrfs
parent6008859b6c6ea0991f530b125132174893903e3b (diff)
downloadlinux-4a4f8fe2b0230c22aba40c9f8ea7b9c6fcfc8417.tar.xz
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 <fdmanana@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs')
-rw-r--r--fs/btrfs/file.c2
-rw-r--r--fs/btrfs/fs.h16
-rw-r--r--fs/btrfs/inode.c4
-rw-r--r--fs/btrfs/ioctl.c2
-rw-r--r--fs/btrfs/sysfs.c2
-rw-r--r--fs/btrfs/transaction.c2
6 files changed, 22 insertions, 6 deletions
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 004c53482f05..723f0c70452e 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 2bd9bedc7095..d04b729cbdf3 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 3b3aec302c33..c9317c047587 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 848b7e6f6421..7ab21283fae8 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 e07be193323a..21ab8b9b62ce 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 3aa59cfa4ab0..f5db3a483f40 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;