ext4: don't call ext4_error while block group is locked

While in ext4_validate_block_bitmap(), if an block allocation bitmap
is found to be invalid, we call ext4_error() while the block group is
still locked.  This causes ext4_commit_super() to call a function
which might sleep while in an atomic context.

There's no need to keep the block group locked at this point, so hoist
the ext4_error() call up to ext4_validate_block_bitmap() and release
the block group spinlock before calling ext4_error().

The reported stack trace can be found at:

	http://article.gmane.org/gmane.comp.file-systems.ext4/33731

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

2 files changed, 37 insertions, 26 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index d23b31ca9d7a..1b5089067d01 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -280,14 +280,18 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
         return desc;
 }
 
-static int ext4_valid_block_bitmap(struct super_block *sb,
-                                   struct ext4_group_desc *desc,
-                                   unsigned int block_group,
-                                   struct buffer_head *bh)
+/*
+ * Return the block number which was discovered to be invalid, or 0 if
+ * the block bitmap is valid.
+ */
+static ext4_fsblk_t ext4_valid_block_bitmap(struct super_block *sb,
+                                            struct ext4_group_desc *desc,
+                                            unsigned int block_group,
+                                            struct buffer_head *bh)
 {
         ext4_grpblk_t offset;
         ext4_grpblk_t next_zero_bit;
-        ext4_fsblk_t bitmap_blk;
+        ext4_fsblk_t blk;
         ext4_fsblk_t group_first_block;
 
         if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
@@ -297,37 +301,33 @@ static int ext4_valid_block_bitmap(struct super_block *sb,
                  * or it has to also read the block group where the bitmaps
                  * are located to verify they are set.
                  */
-                return 1;
+                return 0;
         }
         group_first_block = ext4_group_first_block_no(sb, block_group);
 
         /* check whether block bitmap block number is set */
-        bitmap_blk = ext4_block_bitmap(sb, desc);
-        offset = bitmap_blk - group_first_block;
+        blk = ext4_block_bitmap(sb, desc);
+        offset = blk - group_first_block;
         if (!ext4_test_bit(offset, bh->b_data))
                 /* bad block bitmap */
-                goto err_out;
+                return blk;
 
         /* check whether the inode bitmap block number is set */
-        bitmap_blk = ext4_inode_bitmap(sb, desc);
-        offset = bitmap_blk - group_first_block;
+        blk = ext4_inode_bitmap(sb, desc);
+        offset = blk - group_first_block;
         if (!ext4_test_bit(offset, bh->b_data))
                 /* bad block bitmap */
-                goto err_out;
+                return blk;
 
         /* check whether the inode table block number is set */
-        bitmap_blk = ext4_inode_table(sb, desc);
-        offset = bitmap_blk - group_first_block;
+        blk = ext4_inode_table(sb, desc);
+        offset = blk - group_first_block;
         next_zero_bit = ext4_find_next_zero_bit(bh->b_data,
                                 offset + EXT4_SB(sb)->s_itb_per_group,
                                 offset);
-        if (next_zero_bit >= offset + EXT4_SB(sb)->s_itb_per_group)
-                /* good bitmap for inode tables */
-                return 1;
-
-err_out:
-        ext4_error(sb, "Invalid block bitmap - block_group = %d, block = %llu",
-                        block_group, bitmap_blk);
+        if (next_zero_bit < offset + EXT4_SB(sb)->s_itb_per_group)
+                /* bad bitmap for inode tables */
+                return blk;
         return 0;
 }
 
@@ -336,14 +336,26 @@ void ext4_validate_block_bitmap(struct super_block *sb,
                                unsigned int block_group,
                                struct buffer_head *bh)
 {
+        ext4_fsblk_t    blk;
+
         if (buffer_verified(bh))
                 return;
 
         ext4_lock_group(sb, block_group);
-        if (ext4_valid_block_bitmap(sb, desc, block_group, bh) &&
-            ext4_block_bitmap_csum_verify(sb, block_group, desc, bh,
-                                          EXT4_BLOCKS_PER_GROUP(sb) / 8))
-                set_buffer_verified(bh);
+        blk = ext4_valid_block_bitmap(sb, desc, block_group, bh);
+        if (unlikely(blk != 0)) {
+                ext4_unlock_group(sb, block_group);
+                ext4_error(sb, "bg %u: block %llu: invalid block bitmap",
+                           block_group, blk);
+                return;
+        }
+        if (unlikely(!ext4_block_bitmap_csum_verify(sb, block_group,
+                        desc, bh, EXT4_BLOCKS_PER_GROUP(sb) / 8))) {
+                ext4_unlock_group(sb, block_group);
+                ext4_error(sb, "bg %u: bad block bitmap checksum", block_group);
+                return;
+        }
+        set_buffer_verified(bh);
         ext4_unlock_group(sb, block_group);
 }
 
diff --git a/fs/ext4/bitmap.c b/fs/ext4/bitmap.c
index f8716eab9995..5c2d1813ebe9 100644
--- a/fs/ext4/bitmap.c
+++ b/fs/ext4/bitmap.c
@@ -79,7 +79,6 @@ int ext4_block_bitmap_csum_verify(struct super_block *sb, ext4_group_t group,
         if (provided == calculated)
                 return 1;
 
-        ext4_error(sb, "Bad block bitmap checksum: block_group = %u", group);
         return 0;
 }