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>

diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 4bda2f75d426953227370a8396c83fbd0eb06427..2d36223d5f579fa9817b5f861ca4887a32bc7bba 100644 (file)
--- 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 546c7dd869e19176e77cb54278e9bdfc2b520da4..e8ded13b5cb133ab22d731d5a3cc351d8d0c3272 100644 (file)
--- 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 7f43fde9554b9755f724079bd1fdd8efa1f0b3f4..1fbf0906ae2eff6cff7625bf76de9543612d1ac5 100644 (file)
--- 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;