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SubjectRe: 3.5.1 ext4_ sleeping while atomic bug.
Hi Dave,

Thanks for the bug report! The following should address the bug which
you found.

- Ted

From 05ca87aa00121756b5d41f3d71eb8b51bed3bc92 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@mit.edu>
Date: Fri, 10 Aug 2012 13:57:52 -0400
Subject: [PATCH] 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
---
fs/ext4/balloc.c | 62 +++++++++++++++++++++++++++++++++-----------------------
fs/ext4/bitmap.c | 1 -
2 files changed, 37 insertions(+), 26 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index d23b31c..1b50890 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 f8716ea..5c2d181 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;
}

--
1.7.12.rc0.22.gcdd159b


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