ext4: Replace lock/unlock_super() with an explicit lock for resizing

    
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>

3 files changed, 20 insertions, 17 deletions

diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 4bda2f75d42..2d36223d5f5 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 546c7dd869e..e8ded13b5cb 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 7f43fde9554..1fbf0906ae2 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;