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>

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)

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)

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;
 }

fs/ext4/mmp.c

@@ -57,16 +57,12 @@ static int write_mmp_block_thawed(struct super_block *sb,
 
 static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
 {
-	int err;
-
 	/*
 	 * We protect against freezing so that we don't create dirty buffers
 	 * on frozen filesystem.
 	 */
-	sb_start_write(sb);
-	err = write_mmp_block_thawed(sb, bh);
-	sb_end_write(sb);
-	return err;
+	scoped_guard(super_write, sb)
+		return write_mmp_block_thawed(sb, bh);
 }
 
 /*

fs/open.c

@@ -191,12 +191,9 @@ int do_ftruncate(struct file *file, loff_t length, int small)
 	if (error)
 		return error;
 
-	sb_start_write(inode->i_sb);
-	error = do_truncate(file_mnt_idmap(file), dentry, length,
-			    ATTR_MTIME | ATTR_CTIME, file);
-	sb_end_write(inode->i_sb);
-
-	return error;
+	scoped_guard(super_write, inode->i_sb)
+		return do_truncate(file_mnt_idmap(file), dentry, length,
+				   ATTR_MTIME | ATTR_CTIME, file);
 }
 
 int do_sys_ftruncate(unsigned int fd, loff_t length, int small)

fs/xfs/xfs_ioctl.c

@@ -1408,10 +1408,8 @@ xfs_file_ioctl(
 
 		trace_xfs_ioc_free_eofblocks(mp, &icw, _RET_IP_);
 
-		sb_start_write(mp->m_super);
-		error = xfs_blockgc_free_space(mp, &icw);
-		sb_end_write(mp->m_super);
-		return error;
+		guard(super_write)(mp->m_super);
+		return xfs_blockgc_free_space(mp, &icw);
 	}
 
 	case XFS_IOC_EXCHANGE_RANGE:

include/linux/fs/super.h

@@ -125,6 +125,11 @@ static inline void sb_start_write(struct super_block *sb)
 	__sb_start_write(sb, SB_FREEZE_WRITE);
 }
 
+DEFINE_GUARD(super_write,
+	     struct super_block *,
+	     sb_start_write(_T),
+	     sb_end_write(_T))
+
 static inline bool sb_start_write_trylock(struct super_block *sb)
 {
 	return __sb_start_write_trylock(sb, SB_FREEZE_WRITE);