Merge patch series "fs: introduce super write guard"

Christian Brauner <brauner@kernel.org> says:

I'm in the process of adding a few more guards for vfs constructs.
I've chosen the easy case of super_start_write() and super_end_write()
and converted eligible callers. I think long-term we can move a lot of
the manual placement to completely rely on guards - where sensible.

* patches from https://patch.msgid.link/20251104-work-guards-v1-0-5108ac78a171@kernel.org:
  xfs: use super write guard in xfs_file_ioctl()
  open: use super write guard in do_ftruncate()
  btrfs: use super write guard in relocating_repair_kthread()
  ext4: use super write guard in write_mmp_block()
  btrfs: use super write guard in sb_start_write()
  btrfs: use super write guard btrfs_run_defrag_inode()
  btrfs: use super write guard in btrfs_reclaim_bgs_work()
  fs: add super_write_guard

Link: https://patch.msgid.link/20251104-work-guards-v1-0-5108ac78a171@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

3 files changed, 10 insertions, 16 deletions

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 5322ef2ae015..08cdda47509f 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1850,12 +1850,10 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 	if (!btrfs_should_reclaim(fs_info))
 		return;
 
-	sb_start_write(fs_info->sb);
+	guard(super_write)(fs_info->sb);
 
-	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
-		sb_end_write(fs_info->sb);
+	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE))
 		return;
-	}
 
 	/*
 	 * Long running balances can keep us blocked here for eternity, so
@@ -1863,7 +1861,6 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 	 */
 	if (!mutex_trylock(&fs_info->reclaim_bgs_lock)) {
 		btrfs_exclop_finish(fs_info);
-		sb_end_write(fs_info->sb);
 		return;
 	}
 
@@ -1947,7 +1944,7 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 		/*
 		 * Get out fast, in case we're read-only or unmounting the
 		 * filesystem. It is OK to drop block groups from the list even
-		 * for the read-only case. As we did sb_start_write(),
+		 * for the read-only case. As we did take the super write lock,
 		 * "mount -o remount,ro" won't happen and read-only filesystem
 		 * means it is forced read-only due to a fatal error. So, it
 		 * never gets back to read-write to let us reclaim again.
@@ -2030,7 +2027,6 @@ end:
 	list_splice_tail(&retry_list, &fs_info->reclaim_bgs);
 	spin_unlock(&fs_info->unused_bgs_lock);
 	btrfs_exclop_finish(fs_info);
-	sb_end_write(fs_info->sb);
 }
 
 void btrfs_reclaim_bgs(struct btrfs_fs_info *fs_info)
diff --git a/fs/btrfs/defrag.c b/fs/btrfs/defrag.c
index 7b277934f66f..35fb8ee164dc 100644
--- a/fs/btrfs/defrag.c
+++ b/fs/btrfs/defrag.c
@@ -254,10 +254,9 @@ again:
 	range.extent_thresh = defrag->extent_thresh;
 	file_ra_state_init(ra, inode->vfs_inode.i_mapping);
 
-	sb_start_write(fs_info->sb);
-	ret = btrfs_defrag_file(inode, ra, &range, defrag->transid,
-				BTRFS_DEFRAG_BATCH);
-	sb_end_write(fs_info->sb);
+	scoped_guard(super_write, fs_info->sb)
+		ret = btrfs_defrag_file(inode, ra, &range,
+					defrag->transid, BTRFS_DEFRAG_BATCH);
 	iput(&inode->vfs_inode);
 
 	if (ret < 0)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2bec544d8ba3..88065e52184c 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4660,12 +4660,12 @@ static int balance_kthread(void *data)
 	struct btrfs_fs_info *fs_info = data;
 	int ret = 0;
 
-	sb_start_write(fs_info->sb);
+	guard(super_write)(fs_info->sb);
+
 	mutex_lock(&fs_info->balance_mutex);
 	if (fs_info->balance_ctl)
 		ret = btrfs_balance(fs_info, fs_info->balance_ctl, NULL);
 	mutex_unlock(&fs_info->balance_mutex);
-	sb_end_write(fs_info->sb);
 
 	return ret;
 }
@@ -8177,12 +8177,12 @@ static int relocating_repair_kthread(void *data)
 	target = cache->start;
 	btrfs_put_block_group(cache);
 
-	sb_start_write(fs_info->sb);
+	guard(super_write)(fs_info->sb);
+
 	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
 		btrfs_info(fs_info,
 			   "zoned: skip relocating block group %llu to repair: EBUSY",
 			   target);
-		sb_end_write(fs_info->sb);
 		return -EBUSY;
 	}
 
@@ -8210,7 +8210,6 @@ out:
 		btrfs_put_block_group(cache);
 	mutex_unlock(&fs_info->reclaim_bgs_lock);
 	btrfs_exclop_finish(fs_info);
-	sb_end_write(fs_info->sb);
 
 	return ret;
 }