ext4: fix error processing in mb_free_blocks

PATCH In review Shen Feng 2 participants 3 messages May 29, 2008 ext4 file system

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Shen Feng

author

2008-05-29 03:23 UTC #0 lore raw

PATCH 1/1 ext4: fix error processing in mb_free_blocks

The error processing of the return value of mb_free_blocks is meanless because it only return 0. This fix includes *make mb_free_blocks return void
*remove the error processing part in callers *unlock group before calling ext4_error in mb_free_blocks

Signed-off-by Shen Feng <[email protected]>

---
 fs/ext4/mballoc.c |   13 +++++--------
 1 files changed, 5 insertions(+), 8 deletions(-)

fs/ext4/mballoc.c +5 -8

index a30a35d..6180ebc 100644
@@ -1044,7 +1044,7 @@ static void mb_set_bits(spinlock_t *lock, void *bm, int cur, int len)
 	}
 }
 
-static int mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
+static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
 			  int first, int count)
 {
 	int block = 0;

@@ -1084,11 +1084,12 @@ static int mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
 			blocknr += block;
 			blocknr +=
 			    le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
-
+			ext4_unlock_group(sb, e4b->bd_group);
 			ext4_error(sb, __func__, "double-free of inode"
 				   " %lu's block %llu(bit %u in group %lu)\n",
 				   inode ? inode->i_ino : 0, blocknr, block,
 				   e4b->bd_group);
+			ext4_lock_group(sb, e4b->bd_group);
 		}
 		mb_clear_bit(block, EXT4_MB_BITMAP(e4b));
 		e4b->bd_info->bb_counters[order]++;

@@ -1126,8 +1127,6 @@ static int mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
 		} while (1);
 	}
 	mb_check_buddy(e4b);
-
-	return 0;
 }
 
 static int mb_find_extent(struct ext4_buddy *e4b, int order, int block,

@@ -2561,8 +2560,7 @@ ext4_mb_free_committed_blocks(struct super_block *sb)
 		ext4_lock_group(sb, md->group);
 		for (i = 0; i < md->num; i++) {
 			mb_debug(" %u", md->blocks[i]);
-			err = mb_free_blocks(NULL, &e4b, md->blocks[i], 1);
-			BUG_ON(err != 0);
+			mb_free_blocks(NULL, &e4b, md->blocks[i], 1);
 		}
 		mb_debug("\n");
 		ext4_unlock_group(sb, md->group);

@@ -4326,10 +4324,9 @@ do_more:
 		ext4_mb_free_metadata(handle, &e4b, block_group, bit, count);
 	} else {
 		ext4_lock_group(sb, block_group);
-		err = mb_free_blocks(inode, &e4b, bit, count);
+		mb_free_blocks(inode, &e4b, bit, count);
 		ext4_mb_return_to_preallocation(inode, &e4b, block, count);
 		ext4_unlock_group(sb, block_group);
-		BUG_ON(err != 0);
 	}
 
 	spin_lock(sb_bgl_lock(sbi, block_group));

Signature · 1 line

1.5.4.5

Andrew Morton

2008-05-29 04:30 UTC #1 lore raw

Quoted 4 lines · On Thu, 29 May 2008 11:21:18 +0800 Shen Feng <[email protected]> wrote:

The error processing of the return value of mb_free_blocks is meanless because it only return 0. This fix includes *make mb_free_blocks return void
*remove the error processing part in callers

This:

Quoted 1 line

*unlock group before calling ext4_error in mb_free_blocks

fixes a potential deadlock.

Quoted 4 lines

fs/ext4/mballoc.c +0 -0

@@ -1084,11 +1084,12 @@ static int mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
 			blocknr += block;
 			blocknr +=
 			    le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);

fs/ext4/mballoc.c static int mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, · line 1095

Quoted 10 lines

fs/ext4/mballoc.c +2 -1

-
+			ext4_unlock_group(sb, e4b->bd_group);
 			ext4_error(sb, __func__, "double-free of inode"
 				   " %lu's block %llu(bit %u in group %lu)\n",
 				   inode ? inode->i_ino : 0, blocknr, block,
 				   e4b->bd_group);
+			ext4_lock_group(sb, e4b->bd_group);
 		}
 		mb_clear_bit(block, EXT4_MB_BITMAP(e4b));
 		e4b->bd_info->bb_counters[order]++;

but are we sure we can just drop the lock and then cheerfully proceed? Whatever data that lock is protecting might have changed..

A safer-looking fix would be to return an error from mb_free_blocks() and handle the in the caller, once the ext4_unlock_group() has been performed.

Shen Feng

author

2008-05-29 05:24 UTC #2 lore raw

Andrew Morton Wrote:

Quoted 22 lines · On Thu, 29 May 2008 11:21:18 +0800 Shen Feng <[email protected]> wrote:

Quoted 5 lines
The error processing of the return value of mb_free_blocks is meanless because it only return 0. This fix includes *make mb_free_blocks return void
*remove the error processing part in callers
This:
Quoted 1 line
*unlock group before calling ext4_error in mb_free_blocks
fixes a potential deadlock.
Quoted 9 lines
fs/ext4/mballoc.c +1 -1
@@ -1084,11 +1084,12 @@ static int mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
 			blocknr += block;
 			blocknr +=
 			    le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
-
+			ext4_unlock_group(sb, e4b->bd_group);
 			ext4_error(sb, __func__, "double-free of inode"
 				   " %lu's block %llu(bit %u in group %lu)\n",
 				   inode ? inode->i_ino : 0, blocknr, block,

Quoted 8 lines

fs/ext4/mballoc.c static int mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, · line 1095
Quoted 5 lines
fs/ext4/mballoc.c +1 -0
 				   e4b->bd_group);
+			ext4_lock_group(sb, e4b->bd_group);
 		}
 		mb_clear_bit(block, EXT4_MB_BITMAP(e4b));
 		e4b->bd_info->bb_counters[order]++;
but are we sure we can just drop the lock and then cheerfully proceed? Whatever data that lock is protecting might have changed..

That's a real question to me when I fixed this.
I got the similar code in balloc.c from line 740 in ext4_free_blocks_sb.

		if (!ext4_clear_bit_atomic(sb_bgl_lock(sbi, block_group),
						bit + i, bitmap_bh->b_data)) {
			jbd_unlock_bh_state(bitmap_bh);
			ext4_error(sb, __func__,
				   "bit already cleared for block %llu",
				   (ext4_fsblk_t)(block + i));
			jbd_lock_bh_state(bitmap_bh);
			BUFFER_TRACE(bitmap_bh, "bit already cleared");
		} else {
			group_freed++;
		}

So I did the same fix.
Maybe this also needs to be fixed.

Quoted 7 lines

A safer-looking fix would be to return an error from mb_free_blocks() and handle the in the caller, once the ext4_unlock_group() has been performed.