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ext4: fix lock order problem in ext4_move_extents()
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ext4_move_extents() checks the logical block contiguousness
of original file with ext4_find_extent() and mext_next_extent().
Therefore the extent which ext4_ext_path structure indicates
must not be changed between above functions.

But in current implementation, there is no i_data_sem protection
between ext4_ext_find_extent() and mext_next_extent().  So the extent
which ext4_ext_path structure indicates may be overwritten by
delalloc.  As a result, ext4_move_extents() will exchange wrong blocks
between original and donor files.  I change the place where
acquire/release i_data_sem to solve this problem.

Moreover, I changed move_extent_per_page() to start transaction first,
and then acquire i_data_sem.  Without this change, there is a
possibility of the deadlock between mmap() and ext4_move_extents():

* NOTE: "A", "B" and "C" mean different processes

A-1: ext4_ext_move_extents() acquires i_data_sem of two inodes.

B:   do_page_fault() starts the transaction (T),
     and then tries to acquire i_data_sem.
     But process "A" is already holding it, so it is kept waiting.

C:   While "A" and "B" running, kjournald2 tries to commit transaction (T)
     but it is under updating, so kjournald2 waits for it.

A-2: Call ext4_journal_start with holding i_data_sem,
     but transaction (T) is locked.

Signed-off-by: Akira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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Akira Fujita authored and Theodore Ts'o committed Nov 23, 2009
1 parent f868a48 commit fc04cb4
Showing 1 changed file with 53 additions and 64 deletions.
117 changes: 53 additions & 64 deletions fs/ext4/move_extent.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -77,12 +77,14 @@ static int
mext_next_extent(struct inode *inode, struct ext4_ext_path *path,
struct ext4_extent **extent)
{
struct ext4_extent_header *eh;
int ppos, leaf_ppos = path->p_depth;

ppos = leaf_ppos;
if (EXT_LAST_EXTENT(path[ppos].p_hdr) > path[ppos].p_ext) {
/* leaf block */
*extent = ++path[ppos].p_ext;
path[ppos].p_block = ext_pblock(path[ppos].p_ext);
return 0;
}

Expand Down Expand Up @@ -119,9 +121,18 @@ mext_next_extent(struct inode *inode, struct ext4_ext_path *path,
ext_block_hdr(path[cur_ppos+1].p_bh);
}

path[leaf_ppos].p_ext = *extent = NULL;

eh = path[leaf_ppos].p_hdr;
if (le16_to_cpu(eh->eh_entries) == 0)
/* empty leaf is found */
return -ENODATA;

/* leaf block */
path[leaf_ppos].p_ext = *extent =
EXT_FIRST_EXTENT(path[leaf_ppos].p_hdr);
path[leaf_ppos].p_block =
ext_pblock(path[leaf_ppos].p_ext);
return 0;
}
}
Expand Down Expand Up @@ -155,40 +166,15 @@ mext_check_null_inode(struct inode *inode1, struct inode *inode2,
}

/**
* mext_double_down_read - Acquire two inodes' read semaphore
*
* @orig_inode: original inode structure
* @donor_inode: donor inode structure
* Acquire read semaphore of the two inodes (orig and donor) by i_ino order.
*/
static void
mext_double_down_read(struct inode *orig_inode, struct inode *donor_inode)
{
struct inode *first = orig_inode, *second = donor_inode;

/*
* Use the inode number to provide the stable locking order instead
* of its address, because the C language doesn't guarantee you can
* compare pointers that don't come from the same array.
*/
if (donor_inode->i_ino < orig_inode->i_ino) {
first = donor_inode;
second = orig_inode;
}

down_read(&EXT4_I(first)->i_data_sem);
down_read(&EXT4_I(second)->i_data_sem);
}

/**
* mext_double_down_write - Acquire two inodes' write semaphore
* double_down_write_data_sem - Acquire two inodes' write lock of i_data_sem
*
* @orig_inode: original inode structure
* @donor_inode: donor inode structure
* Acquire write semaphore of the two inodes (orig and donor) by i_ino order.
* Acquire write lock of i_data_sem of the two inodes (orig and donor) by
* i_ino order.
*/
static void
mext_double_down_write(struct inode *orig_inode, struct inode *donor_inode)
double_down_write_data_sem(struct inode *orig_inode, struct inode *donor_inode)
{
struct inode *first = orig_inode, *second = donor_inode;

Expand All @@ -207,28 +193,14 @@ mext_double_down_write(struct inode *orig_inode, struct inode *donor_inode)
}

/**
* mext_double_up_read - Release two inodes' read semaphore
* double_up_write_data_sem - Release two inodes' write lock of i_data_sem
*
* @orig_inode: original inode structure to be released its lock first
* @donor_inode: donor inode structure to be released its lock second
* Release read semaphore of two inodes (orig and donor).
* Release write lock of i_data_sem of two inodes (orig and donor).
*/
static void
mext_double_up_read(struct inode *orig_inode, struct inode *donor_inode)
{
up_read(&EXT4_I(orig_inode)->i_data_sem);
up_read(&EXT4_I(donor_inode)->i_data_sem);
}

/**
* mext_double_up_write - Release two inodes' write semaphore
*
* @orig_inode: original inode structure to be released its lock first
* @donor_inode: donor inode structure to be released its lock second
* Release write semaphore of two inodes (orig and donor).
*/
static void
mext_double_up_write(struct inode *orig_inode, struct inode *donor_inode)
double_up_write_data_sem(struct inode *orig_inode, struct inode *donor_inode)
{
up_write(&EXT4_I(orig_inode)->i_data_sem);
up_write(&EXT4_I(donor_inode)->i_data_sem);
Expand Down Expand Up @@ -688,8 +660,6 @@ mext_replace_branches(handle_t *handle, struct inode *orig_inode,
int replaced_count = 0;
int dext_alen;

mext_double_down_write(orig_inode, donor_inode);

/* Get the original extent for the block "orig_off" */
*err = get_ext_path(orig_inode, orig_off, &orig_path);
if (*err)
Expand Down Expand Up @@ -785,7 +755,6 @@ mext_replace_branches(handle_t *handle, struct inode *orig_inode,
kfree(donor_path);
}

mext_double_up_write(orig_inode, donor_inode);
return replaced_count;
}

Expand Down Expand Up @@ -851,13 +820,19 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
* Just swap data blocks between orig and donor.
*/
if (uninit) {
/*
* Protect extent trees against block allocations
* via delalloc
*/
double_down_write_data_sem(orig_inode, donor_inode);
replaced_count = mext_replace_branches(handle, orig_inode,
donor_inode, orig_blk_offset,
block_len_in_page, err);

/* Clear the inode cache not to refer to the old data */
ext4_ext_invalidate_cache(orig_inode);
ext4_ext_invalidate_cache(donor_inode);
double_up_write_data_sem(orig_inode, donor_inode);
goto out2;
}

Expand Down Expand Up @@ -905,6 +880,8 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
/* Release old bh and drop refs */
try_to_release_page(page, 0);

/* Protect extent trees against block allocations via delalloc */
double_down_write_data_sem(orig_inode, donor_inode);
replaced_count = mext_replace_branches(handle, orig_inode, donor_inode,
orig_blk_offset, block_len_in_page,
&err2);
Expand All @@ -913,14 +890,18 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
block_len_in_page = replaced_count;
replaced_size =
block_len_in_page << orig_inode->i_blkbits;
} else
} else {
double_up_write_data_sem(orig_inode, donor_inode);
goto out;
}
}

/* Clear the inode cache not to refer to the old data */
ext4_ext_invalidate_cache(orig_inode);
ext4_ext_invalidate_cache(donor_inode);

double_up_write_data_sem(orig_inode, donor_inode);

if (!page_has_buffers(page))
create_empty_buffers(page, 1 << orig_inode->i_blkbits, 0);

Expand Down Expand Up @@ -1236,16 +1217,16 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
return -EINVAL;
}

/* protect orig and donor against a truncate */
/* Protect orig and donor inodes against a truncate */
ret1 = mext_inode_double_lock(orig_inode, donor_inode);
if (ret1 < 0)
return ret1;

mext_double_down_read(orig_inode, donor_inode);
/* Protect extent tree against block allocations via delalloc */
double_down_write_data_sem(orig_inode, donor_inode);
/* Check the filesystem environment whether move_extent can be done */
ret1 = mext_check_arguments(orig_inode, donor_inode, orig_start,
donor_start, &len, *moved_len);
mext_double_up_read(orig_inode, donor_inode);
if (ret1)
goto out;

Expand Down Expand Up @@ -1308,6 +1289,10 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
ext4_ext_get_actual_len(ext_cur), block_end + 1) -
max(le32_to_cpu(ext_cur->ee_block), block_start);

/* Discard preallocations of two inodes */
ext4_discard_preallocations(orig_inode);
ext4_discard_preallocations(donor_inode);

while (!last_extent && le32_to_cpu(ext_cur->ee_block) <= block_end) {
seq_blocks += add_blocks;

Expand Down Expand Up @@ -1359,14 +1344,14 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
seq_start = le32_to_cpu(ext_cur->ee_block);
rest_blocks = seq_blocks;

/* Discard preallocations of two inodes */
down_write(&EXT4_I(orig_inode)->i_data_sem);
ext4_discard_preallocations(orig_inode);
up_write(&EXT4_I(orig_inode)->i_data_sem);

down_write(&EXT4_I(donor_inode)->i_data_sem);
ext4_discard_preallocations(donor_inode);
up_write(&EXT4_I(donor_inode)->i_data_sem);
/*
* Up semaphore to avoid following problems:
* a. transaction deadlock among ext4_journal_start,
* ->write_begin via pagefault, and jbd2_journal_commit
* b. racing with ->readpage, ->write_begin, and ext4_get_block
* in move_extent_per_page
*/
double_up_write_data_sem(orig_inode, donor_inode);

while (orig_page_offset <= seq_end_page) {

Expand All @@ -1381,14 +1366,14 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
/* Count how many blocks we have exchanged */
*moved_len += block_len_in_page;
if (ret1 < 0)
goto out;
break;
if (*moved_len > len) {
ext4_error(orig_inode->i_sb, __func__,
"We replaced blocks too much! "
"sum of replaced: %llu requested: %llu",
*moved_len, len);
ret1 = -EIO;
goto out;
break;
}

orig_page_offset++;
Expand All @@ -1400,6 +1385,10 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
block_len_in_page = rest_blocks;
}

double_down_write_data_sem(orig_inode, donor_inode);
if (ret1 < 0)
break;

/* Decrease buffer counter */
if (holecheck_path)
ext4_ext_drop_refs(holecheck_path);
Expand Down Expand Up @@ -1429,7 +1418,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
ext4_ext_drop_refs(holecheck_path);
kfree(holecheck_path);
}

double_up_write_data_sem(orig_inode, donor_inode);
ret2 = mext_inode_double_unlock(orig_inode, donor_inode);

if (ret1)
Expand Down

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