Commit 2de8807b authored by Amir Goldstein's avatar Amir Goldstein Committed by Theodore Ts'o
Browse files

ext4: synchronize ext4_mb_init_group() with buddy page lock 



The old routines ext4_mb_[get|put]_buddy_cache_lock(), which used
to take grp->alloc_sem for all groups on the buddy page have been
replaced with the routines ext4_mb_[get|put]_buddy_page_lock().

The new routines take both buddy and bitmap page locks to protect
against concurrent init of groups on the same buddy page.

The GROUP_NEED_INIT flag is tested again under page lock to check
if the group was initialized by another caller.

Signed-off-by: default avatarAmir Goldstein <amir73il@users.sf.net>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent e73a347b

fs/ext4/mballoc.c

+62 −113
Original line number Diff line number Diff line
@@ -957,22 +957,21 @@ out: 
}



/*

 * lock the group_info alloc_sem of all the groups

 * belonging to the same buddy cache page. This

 * make sure other parallel operation on the buddy

 * cache doesn't happen  whild holding the buddy cache

 * lock

 * Lock the buddy and bitmap pages. This make sure other parallel init_group

 * on the same buddy page doesn't happen whild holding the buddy page lock.

 * Return locked buddy and bitmap pages on e4b struct. If buddy and bitmap

 * are on the same page e4b->bd_buddy_page is NULL and return value is 0.

 */

static int ext4_mb_get_buddy_cache_lock(struct super_block *sb,

					ext4_group_t group)

static int ext4_mb_get_buddy_page_lock(struct super_block *sb,

		ext4_group_t group, struct ext4_buddy *e4b)

{

	int i;

	int block, pnum;

	struct inode *inode = EXT4_SB(sb)->s_buddy_cache;

	int block, pnum, poff;

	int blocks_per_page;

	int groups_per_page;

	ext4_group_t ngroups = ext4_get_groups_count(sb);

	ext4_group_t first_group;

	struct ext4_group_info *grp;

	struct page *page;



	e4b->bd_buddy_page = NULL;

	e4b->bd_bitmap_page = NULL;



	blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;

	/*
@@ -982,57 +981,40 @@ static int ext4_mb_get_buddy_cache_lock(struct super_block *sb, 
	 */

	block = group * 2;

	pnum = block / blocks_per_page;

	first_group = pnum * blocks_per_page / 2;



	groups_per_page = blocks_per_page >> 1;

	if (groups_per_page == 0)

		groups_per_page = 1;

	/* read all groups the page covers into the cache */

	for (i = 0; i < groups_per_page; i++) {

	poff = block % blocks_per_page;

	page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);

	if (!page)

		return -EIO;

	BUG_ON(page->mapping != inode->i_mapping);

	e4b->bd_bitmap_page = page;

	e4b->bd_bitmap = page_address(page) + (poff * sb->s_blocksize);



		if ((first_group + i) >= ngroups)

			break;

		grp = ext4_get_group_info(sb, first_group + i);

		/* take all groups write allocation

		 * semaphore. This make sure there is

		 * no block allocation going on in any

		 * of that groups

		 */

		down_write_nested(&grp->alloc_sem, i);

	}

	return i;

	if (blocks_per_page >= 2) {

		/* buddy and bitmap are on the same page */

		return 0;

	}



static void ext4_mb_put_buddy_cache_lock(struct super_block *sb,

					 ext4_group_t group, int locked_group)

{

	int i;

	int block, pnum;

	int blocks_per_page;

	ext4_group_t first_group;

	struct ext4_group_info *grp;



	blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;

	/*

	 * the buddy cache inode stores the block bitmap

	 * and buddy information in consecutive blocks.

	 * So for each group we need two blocks.

	 */

	block = group * 2;

	block++;

	pnum = block / blocks_per_page;

	first_group = pnum * blocks_per_page / 2;

	/* release locks on all the groups */

	for (i = 0; i < locked_group; i++) {



		grp = ext4_get_group_info(sb, first_group + i);

		/* take all groups write allocation

		 * semaphore. This make sure there is

		 * no block allocation going on in any

		 * of that groups

		 */

		up_write(&grp->alloc_sem);

	poff = block % blocks_per_page;

	page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);

	if (!page)

		return -EIO;

	BUG_ON(page->mapping != inode->i_mapping);

	e4b->bd_buddy_page = page;

	return 0;

}



static void ext4_mb_put_buddy_page_lock(struct ext4_buddy *e4b)

{

	if (e4b->bd_bitmap_page) {

		unlock_page(e4b->bd_bitmap_page);

		page_cache_release(e4b->bd_bitmap_page);

	}

	if (e4b->bd_buddy_page) {

		unlock_page(e4b->bd_buddy_page);

		page_cache_release(e4b->bd_buddy_page);

	}

}



/*
@@ -1044,93 +1026,60 @@ static noinline_for_stack 
int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)

{



	int ret = 0;

	void *bitmap;

	int blocks_per_page;

	int block, pnum, poff;

	int num_grp_locked = 0;

	struct ext4_group_info *this_grp;

	struct ext4_sb_info *sbi = EXT4_SB(sb);

	struct inode *inode = sbi->s_buddy_cache;

	struct page *page = NULL, *bitmap_page = NULL;

	struct ext4_buddy e4b;

	struct page *page;

	int ret = 0;



	mb_debug(1, "init group %u\n", group);

	blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;

	this_grp = ext4_get_group_info(sb, group);

	/*

	 * This ensures that we don't reinit the buddy cache

	 * page which map to the group from which we are already

	 * allocating. If we are looking at the buddy cache we would

	 * have taken a reference using ext4_mb_load_buddy and that

	 * would have taken the alloc_sem lock.

	 * would have pinned buddy page to page cache.

	 */

	num_grp_locked =  ext4_mb_get_buddy_cache_lock(sb, group);

	if (!EXT4_MB_GRP_NEED_INIT(this_grp)) {

	ret = ext4_mb_get_buddy_page_lock(sb, group, &e4b);

	if (ret || !EXT4_MB_GRP_NEED_INIT(this_grp)) {

		/*

		 * somebody initialized the group

		 * return without doing anything

		 */

		ret = 0;

		goto err;

	}

	/*

	 * the buddy cache inode stores the block bitmap

	 * and buddy information in consecutive blocks.

	 * So for each group we need two blocks.

	 */

	block = group * 2;

	pnum = block / blocks_per_page;

	poff = block % blocks_per_page;

	page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);

	if (page) {

		BUG_ON(page->mapping != inode->i_mapping);



	page = e4b.bd_bitmap_page;

	ret = ext4_mb_init_cache(page, NULL);

		if (ret) {

			unlock_page(page);

	if (ret)

		goto err;

		}

		unlock_page(page);

	}

	if (page == NULL || !PageUptodate(page)) {

	if (!PageUptodate(page)) {

		ret = -EIO;

		goto err;

	}

	mark_page_accessed(page);

	bitmap_page = page;

	bitmap = page_address(page) + (poff * sb->s_blocksize);



	/* init buddy cache */

	block++;

	pnum = block / blocks_per_page;

	poff = block % blocks_per_page;

	page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);

	if (page == bitmap_page) {

	if (e4b.bd_buddy_page == NULL) {

		/*

		 * If both the bitmap and buddy are in

		 * the same page we don't need to force

		 * init the buddy

		 */

		unlock_page(page);

	} else if (page) {

		BUG_ON(page->mapping != inode->i_mapping);

		ret = ext4_mb_init_cache(page, bitmap);

		if (ret) {

			unlock_page(page);

		ret = 0;

		goto err;

	}

		unlock_page(page);

	}

	if (page == NULL || !PageUptodate(page)) {

	/* init buddy cache */

	page = e4b.bd_buddy_page;

	ret = ext4_mb_init_cache(page, e4b.bd_bitmap);

	if (ret)

		goto err;

	if (!PageUptodate(page)) {

		ret = -EIO;

		goto err;

	}

	mark_page_accessed(page);

err:

	ext4_mb_put_buddy_cache_lock(sb, group, num_grp_locked);

	if (bitmap_page)

		page_cache_release(bitmap_page);

	if (page)

		page_cache_release(page);

	ext4_mb_put_buddy_page_lock(&e4b);

	return ret;

}

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