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Commit 08c3a813 authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Theodore Ts'o
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ext4: Clarify the locking details in mballoc 



We don't need to take the alloc_sem lock when we are adding new
groups, since mballoc won't see the new group added until we bump
sbi->s_groups_count.

Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
parent f41c0750

fs/ext4/mballoc.c

+5 −2
Original line number Diff line number Diff line
@@ -928,8 +928,11 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group) 
	blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;

	this_grp = ext4_get_group_info(sb, group);

	/*

	 * This ensures we don't add group

	 * to this buddy cache via resize

	 * 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.

	 */

	num_grp_locked =  ext4_mb_get_buddy_cache_lock(sb, group);

	if (!EXT4_MB_GRP_NEED_INIT(this_grp)) {

fs/ext4/resize.c

+1 −6
Original line number Diff line number Diff line
@@ -746,7 +746,6 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input) 
	struct inode *inode = NULL;

	handle_t *handle;

	int gdb_off, gdb_num;

	int num_grp_locked = 0;

	int err, err2;



	gdb_num = input->group / EXT4_DESC_PER_BLOCK(sb);
@@ -856,7 +855,6 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input) 
         * using the new disk blocks.

         */



	num_grp_locked = ext4_mb_get_buddy_cache_lock(sb, input->group);

	/* Update group descriptor block for new group */

	gdp = (struct ext4_group_desc *)((char *)primary->b_data +

					 gdb_off * EXT4_DESC_SIZE(sb));
@@ -875,10 +873,8 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input) 
	 * descriptor

	 */

	err = ext4_mb_add_groupinfo(sb, input->group, gdp);

	if (err) {

		ext4_mb_put_buddy_cache_lock(sb, input->group, num_grp_locked);

	if (err)

		goto exit_journal;

	}



	/*

	 * Make the new blocks and inodes valid next.  We do this before
@@ -920,7 +916,6 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input) 


	/* Update the global fs size fields */

	sbi->s_groups_count++;

	ext4_mb_put_buddy_cache_lock(sb, input->group, num_grp_locked);



	ext4_handle_dirty_metadata(handle, NULL, primary);