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ext4: Fix the race between read_inode_bitmap() and ext4_new_inode()
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We need to make sure we update the inode bitmap and clear
EXT4_BG_INODE_UNINIT flag with sb_bgl_lock held, since
ext4_read_inode_bitmap() looks at EXT4_BG_INODE_UNINIT to decide
whether to initialize the inode bitmap each time it is called.
(introduced by commit c806e68.)

ext4_read_inode_bitmap does:

spin_lock(sb_bgl_lock(EXT4_SB(sb), block_group));
if (desc->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
	ext4_init_inode_bitmap(sb, bh, block_group, desc);

and ext4_new_inode does
if (!ext4_set_bit_atomic(sb_bgl_lock(sbi, group),
                   ino, inode_bitmap_bh->b_data))
		   ......
		   ...
spin_lock(sb_bgl_lock(sbi, group));

gdp->bg_flags &= cpu_to_le16(~EXT4_BG_INODE_UNINIT);
i.e., on allocation we update the bitmap then we take the sb_bgl_lock
and clear the EXT4_BG_INODE_UNINIT flag. What can happen is a
parallel ext4_read_inode_bitmap can zero out the bitmap in between
the above ext4_set_bit_atomic and spin_lock(sb_bg_lock..)

The race results in below user visible errors
EXT4-fs error (device sdb1): ext4_free_inode: bit already cleared for inode 168449
EXT4-fs warning (device sdb1): ext4_unlink: Deleting nonexistent file ...
EXT4-fs warning (device sdb1): ext4_rmdir: empty directory has too many links ...
# ls -al /mnt/tmp/f/p369/d3/d6/d39/db2/dee/d10f/d3f/l71
ls: /mnt/tmp/f/p369/d3/d6/d39/db2/dee/d10f/d3f/l71: Stale NFS file handle

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org
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Aneesh Kumar K.V authored and Theodore Ts'o committed Jan 6, 2009
1 parent 3300bed commit 3934186
Showing 1 changed file with 86 additions and 60 deletions.
146 changes: 86 additions & 60 deletions fs/ext4/ialloc.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -572,6 +572,79 @@ static int find_group_other(struct super_block *sb, struct inode *parent,
return -1;
}

/*
* claim the inode from the inode bitmap. If the group
* is uninit we need to take the groups's sb_bgl_lock
* and clear the uninit flag. The inode bitmap update
* and group desc uninit flag clear should be done
* after holding sb_bgl_lock so that ext4_read_inode_bitmap
* doesn't race with the ext4_claim_inode
*/
static int ext4_claim_inode(struct super_block *sb,
struct buffer_head *inode_bitmap_bh,
unsigned long ino, ext4_group_t group, int mode)
{
int free = 0, retval = 0, count;
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, NULL);

spin_lock(sb_bgl_lock(sbi, group));
if (ext4_set_bit(ino, inode_bitmap_bh->b_data)) {
/* not a free inode */
retval = 1;
goto err_ret;
}
ino++;
if ((group == 0 && ino < EXT4_FIRST_INO(sb)) ||
ino > EXT4_INODES_PER_GROUP(sb)) {
spin_unlock(sb_bgl_lock(sbi, group));
ext4_error(sb, __func__,
"reserved inode or inode > inodes count - "
"block_group = %u, inode=%lu", group,
ino + group * EXT4_INODES_PER_GROUP(sb));
return 1;
}
/* If we didn't allocate from within the initialized part of the inode
* table then we need to initialize up to this inode. */
if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {

if (gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
gdp->bg_flags &= cpu_to_le16(~EXT4_BG_INODE_UNINIT);
/* When marking the block group with
* ~EXT4_BG_INODE_UNINIT we don't want to depend
* on the value of bg_itable_unused even though
* mke2fs could have initialized the same for us.
* Instead we calculated the value below
*/

free = 0;
} else {
free = EXT4_INODES_PER_GROUP(sb) -
ext4_itable_unused_count(sb, gdp);
}

/*
* Check the relative inode number against the last used
* relative inode number in this group. if it is greater
* we need to update the bg_itable_unused count
*
*/
if (ino > free)
ext4_itable_unused_set(sb, gdp,
(EXT4_INODES_PER_GROUP(sb) - ino));
}
count = ext4_free_inodes_count(sb, gdp) - 1;
ext4_free_inodes_set(sb, gdp, count);
if (S_ISDIR(mode)) {
count = ext4_used_dirs_count(sb, gdp) + 1;
ext4_used_dirs_set(sb, gdp, count);
}
gdp->bg_checksum = ext4_group_desc_csum(sbi, group, gdp);
err_ret:
spin_unlock(sb_bgl_lock(sbi, group));
return retval;
}

/*
* There are two policies for allocating an inode. If the new inode is
* a directory, then a forward search is made for a block group with both
Expand All @@ -594,7 +667,7 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode)
struct ext4_super_block *es;
struct ext4_inode_info *ei;
struct ext4_sb_info *sbi;
int ret2, err = 0, count;
int ret2, err = 0;
struct inode *ret;
ext4_group_t i;
int free = 0;
Expand Down Expand Up @@ -658,8 +731,13 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode)
if (err)
goto fail;

if (!ext4_set_bit_atomic(sb_bgl_lock(sbi, group),
ino, inode_bitmap_bh->b_data)) {
BUFFER_TRACE(group_desc_bh, "get_write_access");
err = ext4_journal_get_write_access(handle,
group_desc_bh);
if (err)
goto fail;
if (!ext4_claim_inode(sb, inode_bitmap_bh,
ino, group, mode)) {
/* we won it */
BUFFER_TRACE(inode_bitmap_bh,
"call ext4_handle_dirty_metadata");
Expand All @@ -668,10 +746,13 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode)
inode_bitmap_bh);
if (err)
goto fail;
/* zero bit is inode number 1*/
ino++;
goto got;
}
/* we lost it */
ext4_handle_release_buffer(handle, inode_bitmap_bh);
ext4_handle_release_buffer(handle, group_desc_bh);

if (++ino < EXT4_INODES_PER_GROUP(sb))
goto repeat_in_this_group;
Expand All @@ -691,22 +772,6 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode)
goto out;

got:
ino++;
if ((group == 0 && ino < EXT4_FIRST_INO(sb)) ||
ino > EXT4_INODES_PER_GROUP(sb)) {
ext4_error(sb, __func__,
"reserved inode or inode > inodes count - "
"block_group = %u, inode=%lu", group,
ino + group * EXT4_INODES_PER_GROUP(sb));
err = -EIO;
goto fail;
}

BUFFER_TRACE(group_desc_bh, "get_write_access");
err = ext4_journal_get_write_access(handle, group_desc_bh);
if (err)
goto fail;

/* We may have to initialize the block bitmap if it isn't already */
if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM) &&
gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
Expand Down Expand Up @@ -743,49 +808,10 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode)
if (err)
goto fail;
}

spin_lock(sb_bgl_lock(sbi, group));
/* If we didn't allocate from within the initialized part of the inode
* table then we need to initialize up to this inode. */
if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
if (gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
gdp->bg_flags &= cpu_to_le16(~EXT4_BG_INODE_UNINIT);

/* When marking the block group with
* ~EXT4_BG_INODE_UNINIT we don't want to depend
* on the value of bg_itable_unused even though
* mke2fs could have initialized the same for us.
* Instead we calculated the value below
*/

free = 0;
} else {
free = EXT4_INODES_PER_GROUP(sb) -
ext4_itable_unused_count(sb, gdp);
}

/*
* Check the relative inode number against the last used
* relative inode number in this group. if it is greater
* we need to update the bg_itable_unused count
*
*/
if (ino > free)
ext4_itable_unused_set(sb, gdp,
(EXT4_INODES_PER_GROUP(sb) - ino));
}

count = ext4_free_inodes_count(sb, gdp) - 1;
ext4_free_inodes_set(sb, gdp, count);
if (S_ISDIR(mode)) {
count = ext4_used_dirs_count(sb, gdp) + 1;
ext4_used_dirs_set(sb, gdp, count);
}
gdp->bg_checksum = ext4_group_desc_csum(sbi, group, gdp);
spin_unlock(sb_bgl_lock(sbi, group));
BUFFER_TRACE(group_desc_bh, "call ext4_handle_dirty_metadata");
err = ext4_handle_dirty_metadata(handle, NULL, group_desc_bh);
if (err) goto fail;
if (err)
goto fail;

percpu_counter_dec(&sbi->s_freeinodes_counter);
if (S_ISDIR(mode))
Expand Down

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