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authorFilipe Manana <fdmanana@suse.com>2023-10-04 13:38:48 +0300
committerDavid Sterba <dsterba@suse.com>2023-10-12 17:44:17 +0300
commitf9850787969953552266da579d0f1fbf2c2e1c10 (patch)
tree1ba9afba0fd05be401ac6bcd4e9bd4b99dfd3c31 /fs/btrfs
parenta5b8a5f9f8355d27a4f8d0afa93427f16d2f3c1e (diff)
downloadlinux-f9850787969953552266da579d0f1fbf2c2e1c10.tar.xz
btrfs: add and use helpers for reading and writing last_log_commit
Currently, the last_log_commit of a root can be accessed concurrently without any lock protection. Readers can be calling btrfs_inode_in_log() early in a fsync call, which reads a root's last_log_commit, while a writer can change the last_log_commit while a log tree if being synced, at btrfs_sync_log(). Any 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. 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 last_log_commit field of a root using READ_ONCE() and WRITE_ONCE(), and use these helpers everywhere. [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/btrfs_inode.h2
-rw-r--r--fs/btrfs/ctree.h16
-rw-r--r--fs/btrfs/disk-io.c4
-rw-r--r--fs/btrfs/tree-log.c4
4 files changed, 20 insertions, 6 deletions
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 81bf514d988f..d32ef248828e 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -390,7 +390,7 @@ static inline bool btrfs_inode_in_log(struct btrfs_inode *inode, u64 generation)
spin_lock(&inode->lock);
if (inode->logged_trans == generation &&
inode->last_sub_trans <= inode->last_log_commit &&
- inode->last_sub_trans <= inode->root->last_log_commit)
+ inode->last_sub_trans <= btrfs_get_root_last_log_commit(inode->root))
ret = true;
spin_unlock(&inode->lock);
return ret;
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 208a1888ca07..3ebb5229660a 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -194,7 +194,11 @@ struct btrfs_root {
int log_transid;
/* No matter the commit succeeds or not*/
int log_transid_committed;
- /* Just be updated when the commit succeeds. */
+ /*
+ * Just be updated when the commit succeeds. Use
+ * btrfs_get_root_last_log_commit() and btrfs_set_root_last_log_commit()
+ * to access this field.
+ */
int last_log_commit;
pid_t log_start_pid;
@@ -328,6 +332,16 @@ static inline u64 btrfs_root_id(const struct btrfs_root *root)
return root->root_key.objectid;
}
+static inline int btrfs_get_root_last_log_commit(const struct btrfs_root *root)
+{
+ return READ_ONCE(root->last_log_commit);
+}
+
+static inline void btrfs_set_root_last_log_commit(struct btrfs_root *root, int commit_id)
+{
+ WRITE_ONCE(root->last_log_commit, commit_id);
+}
+
/*
* Structure that conveys information about an extent that is going to replace
* all the extents in a file range.
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index ff3802986b3e..fe18c54cec10 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -677,7 +677,7 @@ static void __setup_root(struct btrfs_root *root, struct btrfs_fs_info *fs_info,
atomic_set(&root->nr_swapfiles, 0);
root->log_transid = 0;
root->log_transid_committed = -1;
- root->last_log_commit = 0;
+ btrfs_set_root_last_log_commit(root, 0);
root->anon_dev = 0;
if (!dummy) {
extent_io_tree_init(fs_info, &root->dirty_log_pages,
@@ -1006,7 +1006,7 @@ int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
root->log_root = log_root;
root->log_transid = 0;
root->log_transid_committed = -1;
- root->last_log_commit = 0;
+ btrfs_set_root_last_log_commit(root, 0);
return 0;
}
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 2c4685316c43..28a61a7dd371 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3133,8 +3133,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
* someone else already started it. We use <= and not < because the
* first log transaction has an ID of 0.
*/
- ASSERT(root->last_log_commit <= log_transid);
- root->last_log_commit = log_transid;
+ ASSERT(btrfs_get_root_last_log_commit(root) <= log_transid);
+ btrfs_set_root_last_log_commit(root, log_transid);
out_wake_log_root:
mutex_lock(&log_root_tree->log_mutex);