Skip to content

Commit

Permalink
ext4: synchronize ext4_mb_init_group() with buddy page lock
Browse files Browse the repository at this point in the history 
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: Amir Goldstein <amir73il@users.sf.net>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
  • Loading branch information
Amir Goldstein authored and Theodore Ts'o committed May 10, 2011
1 parent e73a347 commit 2de8807
Showing 1 changed file with 62 additions and 113 deletions.
175 changes: 62 additions & 113 deletions fs/ext4/mballoc.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -957,22 +957,21 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
}

/*
* 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;
/*
Expand All @@ -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);
if (blocks_per_page >= 2) {
/* buddy and bitmap are on the same page */
return 0;
}
return i;

block++;
pnum = block / blocks_per_page;
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_cache_lock(struct super_block *sb,
ext4_group_t group, int locked_group)
static void ext4_mb_put_buddy_page_lock(struct ext4_buddy *e4b)
{
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;
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);
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);
}

}

/*
Expand All @@ -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);
ret = ext4_mb_init_cache(page, NULL);
if (ret) {
unlock_page(page);
goto err;
}
unlock_page(page);
}
if (page == NULL || !PageUptodate(page)) {

page = e4b.bd_bitmap_page;
ret = ext4_mb_init_cache(page, NULL);
if (ret)
goto err;
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);
goto err;
}
unlock_page(page);
ret = 0;
goto err;
}
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;
}

Expand Down

0 comments on commit 2de8807

Please sign in to comment.