ocfs2: Tighten free bit calculation in the global bitmap

When clearing bits in the global bitmap, we do not test the current bit value.
This patch tightens the code by considering the possiblity that the bit being
cleared was already cleared.

Now this should not happen. But we are seeing stray instances in which free
bit count in the global bitmap exceeds the total bit count. In each instance
the bitmap is correct. Only the free bit count is incorrect.

This patch checks the current bit value and increments the free bit count
only if the bit was previously set. It also prints information to allow
us to debug further.

Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>

diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index ba5d97e4a73e8a43e64fc3cfa55fb9b97d4ec6a5..4f7123c2d19d397ee26a28931ada6a2f6fdeb54b 100644 (file)
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -2386,6 +2386,7 @@ static int ocfs2_block_group_clear_bits(handle_t *handle,
        int status;
        unsigned int tmp;
        struct ocfs2_group_desc *undo_bg = NULL;
+       unsigned int bits_cleared = 0;
 
        /* The caller got this descriptor from
         * ocfs2_read_group_descriptor().  Any corruption is a code bug. */
@@ -2413,13 +2414,27 @@ static int ocfs2_block_group_clear_bits(handle_t *handle,
 
        tmp = num_bits;
        while(tmp--) {
-               ocfs2_clear_bit((bit_off + tmp),
-                               (unsigned long *) bg->bg_bitmap);
+               if (ocfs2_test_bit((bit_off + tmp),
+                                  (unsigned long *) bg->bg_bitmap)) {
+                       ocfs2_clear_bit((bit_off + tmp),
+                                       (unsigned long *) bg->bg_bitmap);
+                       bits_cleared++;
+               }
                if (undo_fn)
                        undo_fn(bit_off + tmp,
                                (unsigned long *) undo_bg->bg_bitmap);
        }
-       le16_add_cpu(&bg->bg_free_bits_count, num_bits);
+
+       le16_add_cpu(&bg->bg_free_bits_count, bits_cleared);
+
+       if (num_bits != bits_cleared) {
+               printk(KERN_NOTICE "ocfs2: Trying to clear %u bits at "
+                      "offset %u in group descriptor # %llu (device %s), "
+                      "needed to clear %u bits\n", num_bits, bit_off,
+                      (unsigned long long)le64_to_cpu(bg->bg_blkno),
+                      alloc_inode->i_sb->s_id, bits_cleared);
+       }
+
        if (le16_to_cpu(bg->bg_free_bits_count) > le16_to_cpu(bg->bg_bits)) {
                ocfs2_error(alloc_inode->i_sb, "Group descriptor # %llu has bit"
                            " count %u but claims %u are freed. num_bits %d",