[PATCH 15/49] ext4: Replace lock/unlock_super() with an explicit lock for resizing

Theodore Ts'o
2009-06-08T19:35:14Z

Use a separate lock to protect s_groups_count and the other block
group descriptors which get changed via an on-line resize operation,
so we can stop overloading the use of lock_super().

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
fs/ext4/ext4_sb.h | 1 +
fs/ext4/resize.c | 35 ++++++++++++++++++-----------------
fs/ext4/super.c | 1 +
3 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 4bda2f7..2d36223 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -72,6 +72,7 @@ struct ext4_sb_info {
struct journal_s *s_journal;
struct list_head s_orphan;
struct mutex s_orphan_lock;
+ struct mutex s_resize_lock;
unsigned long s_commit_interval;
u32 s_max_batch_time;
u32 s_min_batch_time;
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 546c7dd..e8ded13 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -193,7 +193,7 @@ static int setup_new_group_blocks(struct super_block *sb,
if (IS_ERR(handle))
return PTR_ERR(handle);

- lock_super(sb);
+ mutex_lock(&sbi->s_resize_lock);
if (input->group != sbi->s_groups_count) {
err = -EBUSY;
goto exit_journal;
@@ -302,7 +302,7 @@ exit_bh:
brelse(bh);

exit_journal:
- unlock_super(sb);
+ mutex_unlock(&sbi->s_resize_lock);
if ((err2 = ext4_journal_stop(handle)) && !err)
err = err2;

@@ -643,11 +643,12 @@ exit_free:
* important part is that the new block and inode counts are in the backup
* superblocks, and the location of the new group metadata in the GDT backups.
*
- * We do not need lock_super() for this, because these blocks are not
- * otherwise touched by the filesystem code when it is mounted. We don't
- * need to worry about last changing from sbi->s_groups_count, because the
- * worst that can happen is that we do not copy the full number of backups
- * at this time. The resize which changed s_groups_count will backup again.
+ * We do not need take the s_resize_lock for this, because these
+ * blocks are not otherwise touched by the filesystem code when it is
+ * mounted. We don't need to worry about last changing from
+ * sbi->s_groups_count, because the worst that can happen is that we
+ * do not copy the full number of backups at this time. The resize
+ * which changed s_groups_count will backup again.
*/
static void update_backups(struct super_block *sb,
int blk_off, char *data, int size)
@@ -809,7 +810,7 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
goto exit_put;
}

- lock_super(sb);
+ mutex_lock(&sbi->s_resize_lock);
if (input->group != sbi->s_groups_count) {
ext4_warning(sb, __func__,
"multiple resizers run on filesystem!");
@@ -840,7 +841,7 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
/*
* OK, now we've set up the new group. Time to make it active.
*
- * Current kernels don't lock all allocations via lock_super(),
+ * We do not lock all allocations via s_resize_lock
* so we have to be safe wrt. concurrent accesses the group
* data. So we need to be careful to set all of the relevant
* group descriptor data etc. *before* we enable the group.
@@ -900,12 +901,12 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
*
* The precise rules we use are:
*
- * * Writers of s_groups_count *must* hold lock_super
+ * * Writers of s_groups_count *must* hold s_resize_lock
* AND
* * Writers must perform a smp_wmb() after updating all dependent
* data and before modifying the groups count
*
- * * Readers must hold lock_super() over the access
+ * * Readers must hold s_resize_lock over the access
* OR
* * Readers must perform an smp_rmb() after reading the groups count
* and before reading any dependent data.
@@ -948,7 +949,7 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
sb->s_dirt = 1;

exit_journal:
- unlock_super(sb);
+ mutex_unlock(&sbi->s_resize_lock);
if ((err2 = ext4_journal_stop(handle)) && !err)
err = err2;
if (!err) {
@@ -986,7 +987,7 @@ int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es,

/* We don't need to worry about locking wrt other resizers just
* yet: we're going to revalidate es->s_blocks_count after
- * taking lock_super() below. */
+ * taking the s_resize_lock below. */
o_blocks_count = ext4_blocks_count(es);
o_groups_count = EXT4_SB(sb)->s_groups_count;

@@ -1056,11 +1057,11 @@ int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es,
goto exit_put;
}

- lock_super(sb);
+ mutex_lock(&EXT4_SB(sb)->s_resize_lock);
if (o_blocks_count != ext4_blocks_count(es)) {
ext4_warning(sb, __func__,
"multiple resizers run on filesystem!");
- unlock_super(sb);
+ mutex_unlock(&EXT4_SB(sb)->s_resize_lock);
ext4_journal_stop(handle);
err = -EBUSY;
goto exit_put;
@@ -1070,14 +1071,14 @@ int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es,
EXT4_SB(sb)->s_sbh))) {
ext4_warning(sb, __func__,
"error %d on journal write access", err);
- unlock_super(sb);
+ mutex_unlock(&EXT4_SB(sb)->s_resize_lock);
ext4_journal_stop(handle);
goto exit_put;
}
ext4_blocks_count_set(es, o_blocks_count + add);
ext4_handle_dirty_metadata(handle, NULL, EXT4_SB(sb)->s_sbh);
sb->s_dirt = 1;
- unlock_super(sb);
+ mutex_unlock(&EXT4_SB(sb)->s_resize_lock);
ext4_debug("freeing blocks %llu through %llu\n", o_blocks_count,
o_blocks_count + add);
/* We add the blocks to the bitmap and set the group need init bit */
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7f43fde..1fbf090 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2646,6 +2646,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
#endif
INIT_LIST_HEAD(&sbi->s_orphan); /* unlinked but open files */
mutex_init(&sbi->s_orphan_lock);
+ mutex_init(&sbi->s_resize_lock);

sb->s_root = NULL;

--
1.6.3.2.1.gb9f7d.dirty