From 08c3a8133810d955d97f7146c50c43e4073f2148 Mon Sep 17 00:00:00 2001
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Date: Wed, 9 Sep 2009 23:50:17 -0400
Subject: [PATCH] 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: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/ext4/mballoc.c | 7 +++++--
fs/ext4/resize.c | 7 +------
2 files changed, 6 insertions(+), 8 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 484c9d10c7fa..d23056d375b3 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -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)) {
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 68b0351fc647..3cfc343c41b5 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -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);
--
2.20.1