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Commit d19de7ed authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

writeback: fix writeback_inodes_wb from writeback_inodes_sb 



When we call writeback_inodes_wb from writeback_inodes_sb we always have
s_umount held, which currently makes the whole operation a no-op.

But if we are called to write out inodes for a specific superblock we always
have s_umount held, so replace the incorrect logic checking for WB_SYNC_ALL
which only worked by coincidence with the proper check for an explicit
superblock argument.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent cf37e972

fs/fs-writeback.c

+23 −38
Original line number Diff line number Diff line
@@ -518,39 +518,19 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc) 
	return ret;

}



static void unpin_sb_for_writeback(struct super_block *sb)

{

	up_read(&sb->s_umount);

	put_super(sb);

}



enum sb_pin_state {

	SB_PINNED,

	SB_NOT_PINNED,

	SB_PIN_FAILED

};



/*

 * For WB_SYNC_NONE writeback, the caller does not have the sb pinned

 * For background writeback the caller does not have the sb pinned

 * before calling writeback. So make sure that we do pin it, so it doesn't

 * go away while we are writing inodes from it.

 */

static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc,

					      struct super_block *sb)

static bool pin_sb_for_writeback(struct super_block *sb)

{

	/*

	 * Caller must already hold the ref for this

	 */

	if (wbc->sync_mode == WB_SYNC_ALL) {

		WARN_ON(!rwsem_is_locked(&sb->s_umount));

		return SB_NOT_PINNED;

	}

	spin_lock(&sb_lock);

	sb->s_count++;

	if (down_read_trylock(&sb->s_umount)) {

		if (sb->s_root) {

			spin_unlock(&sb_lock);

			return SB_PINNED;

			return true;

		}

		/*

		 * umounted, drop rwsem again and fall through to failure
@@ -559,7 +539,7 @@ static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc, 
	}

	sb->s_count--;

	spin_unlock(&sb_lock);

	return SB_PIN_FAILED;

	return false;

}



/*
@@ -638,24 +618,29 @@ static void writeback_inodes_wb(struct bdi_writeback *wb, 
		struct inode *inode = list_entry(wb->b_io.prev,

						 struct inode, i_list);

		struct super_block *sb = inode->i_sb;

		enum sb_pin_state state;



		if (wbc->sb && sb != wbc->sb) {

			/* super block given and doesn't

			   match, skip this inode */

		if (wbc->sb) {

			/*

			 * We are requested to write out inodes for a specific

			 * superblock.  This means we already have s_umount

			 * taken by the caller which also waits for us to

			 * complete the writeout.

			 */

			if (sb != wbc->sb) {

				redirty_tail(inode);

				continue;

			}

		state = pin_sb_for_writeback(wbc, sb);



		if (state == SB_PIN_FAILED) {

			requeue_io(inode);

			WARN_ON(!rwsem_is_locked(&sb->s_umount));



			ret = writeback_sb_inodes(sb, wb, wbc);

		} else {

			if (!pin_sb_for_writeback(sb))

				continue;

		}

			ret = writeback_sb_inodes(sb, wb, wbc);

			drop_super(sb);

		}



		if (state == SB_PINNED)

			unpin_sb_for_writeback(sb);

		if (ret)

			break;

	}