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Date: Fri, 2 Sep 2011 12:08:29 -0700
From: "Darrick J. Wong" <djwong@...ibm.com>
To: Andreas Dilger <adilger.kernel@...ger.ca>
Cc: Theodore Tso <tytso@....edu>,
Sunil Mushran <sunil.mushran@...cle.com>,
Amir Goldstein <amir73il@...il.com>,
linux-kernel <linux-kernel@...r.kernel.org>,
Andi Kleen <andi@...stfloor.org>,
Mingming Cao <cmm@...ibm.com>,
Joel Becker <jlbec@...lplan.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
linux-ext4@...r.kernel.org, Coly Li <colyli@...il.com>
Subject: Re: [PATCH 09/16] ext4: Calculate and verify block bitmap checksum
On Thu, Sep 01, 2011 at 12:08:44AM -0600, Andreas Dilger wrote:
> On 2011-08-31, at 6:31 PM, Darrick J. Wong wrote:
> > Compute and verify the checksum of the block bitmap; this checksum is stored in
> > the block group descriptor.
> >
> > Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
> > ---
> > fs/ext4/balloc.c | 43 ++++++++++++++++++++++++++++++++++---------
> > fs/ext4/ext4.h | 7 ++++++-
> > fs/ext4/ialloc.c | 5 +++++
> > fs/ext4/mballoc.c | 34 ++++++++++++++++++++++++++++++++++
> > 4 files changed, 79 insertions(+), 10 deletions(-)
> >
> >
> > diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> > index f8224ad..36d3020 100644
> > --- a/fs/ext4/balloc.c
> > +++ b/fs/ext4/balloc.c
> > @@ -105,6 +105,10 @@ unsigned ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
> > ext4_free_inodes_set(sb, gdp, 0);
> > ext4_itable_unused_set(sb, gdp, 0);
> > memset(bh->b_data, 0xff, sb->s_blocksize);
> > + ext4_bitmap_csum_set(sb, block_group,
> > + &gdp->bg_block_bitmap_csum, bh,
> > + (EXT4_BLOCKS_PER_GROUP(sb) + 7) /
> > + 8);
> > return 0;
> > }
> > memset(bh->b_data, 0, sb->s_blocksize);
> > @@ -175,6 +179,11 @@ unsigned ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
> > */
> > ext4_mark_bitmap_end(group_blocks, sb->s_blocksize * 8,
> > bh->b_data);
> > + ext4_bitmap_csum_set(sb, block_group,
> > + &gdp->bg_block_bitmap_csum, bh,
> > + (EXT4_BLOCKS_PER_GROUP(sb) + 7) / 8);
> > + gdp->bg_checksum = ext4_group_desc_csum(sbi, block_group,
> > + gdp);
> > }
> > return free_blocks - ext4_group_used_meta_blocks(sb, block_group, gdp);
> > }
> > @@ -232,10 +241,10 @@ 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)
> > +int 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;
> > @@ -312,12 +321,12 @@ ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
> > }
> >
> > if (bitmap_uptodate(bh))
> > - return bh;
> > + goto verify;
> >
> > lock_buffer(bh);
> > if (bitmap_uptodate(bh)) {
> > unlock_buffer(bh);
> > - return bh;
> > + goto verify;
> > }
> > ext4_lock_group(sb, block_group);
> > if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
> > @@ -336,7 +345,7 @@ ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
> > */
> > set_bitmap_uptodate(bh);
> > unlock_buffer(bh);
> > - return bh;
> > + goto verify;
> > }
> > /*
> > * submit the buffer_head for read. We can
> > @@ -353,11 +362,27 @@ ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
> > block_group, bitmap_blk);
> > return NULL;
> > }
> > - ext4_valid_block_bitmap(sb, desc, block_group, bh);
> > +
> > +verify:
> > + if (buffer_verified(bh))
> > + return bh;
> > /*
> > * file system mounted not to panic on error,
> > - * continue with corrupt bitmap
> > + * -EIO with corrupt bitmap
> > */
> > + ext4_lock_group(sb, block_group);
> > + if (!ext4_valid_block_bitmap(sb, desc, block_group, bh) ||
> > + !ext4_bitmap_csum_verify(sb, block_group,
> > + desc->bg_block_bitmap_csum, bh,
> > + (EXT4_BLOCKS_PER_GROUP(sb) + 7) / 8)) {
> > + ext4_unlock_group(sb, block_group);
> > + put_bh(bh);
> > + ext4_error(sb, "Corrupt block bitmap - block_group = %u, "
> > + "block_bitmap = %llu", block_group, bitmap_blk);
> > + return NULL;
> > + }
> > + ext4_unlock_group(sb, block_group);
> > + set_buffer_verified(bh);
> > return bh;
> > }
> >
> > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> > index 248cbd2..df149b3 100644
> > --- a/fs/ext4/ext4.h
> > +++ b/fs/ext4/ext4.h
> > @@ -269,7 +269,8 @@ struct ext4_group_desc
> > __le16 bg_free_inodes_count_lo;/* Free inodes count */
> > __le16 bg_used_dirs_count_lo; /* Directories count */
> > __le16 bg_flags; /* EXT4_BG_flags (INODE_UNINIT, etc) */
> > - __u32 bg_reserved[2]; /* Likely block/inode bitmap checksum */
> > + __u32 bg_reserved[1]; /* unclaimed */
> > + __le32 bg_block_bitmap_csum; /* crc32c(uuid+group+bbitmap) */
>
> Same comment as for the inode bitmap checksum - it should be split into
> two __le16 fields, so that we get at least some coverage for the vast
> majority of existing filesystems.
>
> > __le16 bg_itable_unused_lo; /* Unused inodes count */
> > __le16 bg_checksum; /* crc16(sb_uuid+group+desc) */
> > __le32 bg_block_bitmap_hi; /* Blocks bitmap block MSB */
> > @@ -1731,6 +1732,10 @@ void ext4_bitmap_csum_set(struct super_block *sb, ext4_group_t group,
> > __le32 *csum, struct buffer_head *bh, int sz);
> >
> > /* balloc.c */
> > +extern int ext4_valid_block_bitmap(struct super_block *sb,
> > + struct ext4_group_desc *desc,
> > + unsigned int block_group,
> > + struct buffer_head *bh);
> > extern unsigned int ext4_block_group(struct super_block *sb,
> > ext4_fsblk_t blocknr);
> > extern ext4_grpblk_t ext4_block_group_offset(struct super_block *sb,
> > diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
> > index 53faffc..a335d19 100644
> > --- a/fs/ext4/ialloc.c
> > +++ b/fs/ext4/ialloc.c
> > @@ -984,6 +984,11 @@ got:
> > free = ext4_free_blocks_after_init(sb, group, gdp);
> > gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
> > ext4_free_blks_set(sb, gdp, free);
> > + ext4_bitmap_csum_set(sb, group,
> > + &gdp->bg_block_bitmap_csum,
> > + block_bitmap_bh,
> > + (EXT4_BLOCKS_PER_GROUP(sb) + 7) /
> > + 8);
> > gdp->bg_checksum = ext4_group_desc_csum(sbi, group,
> > gdp);
> > }
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index 17a5a57..8dc3055 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -895,6 +895,33 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
> > if (bh[i] && !buffer_uptodate(bh[i]))
> > goto out;
> >
> > + for (i = 0; i < groups_per_page; i++) {
> > + struct ext4_group_desc *desc;
> > +
> > + if (!bh[i] || !bh[i]->b_end_io)
> > + continue;
>
> Please don't treat pointers as boolean values. I'd prefer to see a
> proper comparison like "bh[i] == NULL" here.
>
> Also, it isn't obvious why the check for b_end_io is needed here?
If b_end_io is set then the block is being read in and needs checking.
BH_Verified would work just as well here and be a little clearer. I think I
had this patch written before I added the BH_Verified flag and forgot to update
this patch. Oops. Good catch.
> > + desc = ext4_get_group_desc(sb, first_group + i, NULL);
> > + if (!desc)
> > + goto out;
> > +
> > + if (buffer_verified(bh[i]))
> > + continue;
> > + ext4_lock_group(sb, first_group + i);
> > + if (!ext4_valid_block_bitmap(sb, desc, first_group + i,
> > + bh[i]) ||
> > + !ext4_bitmap_csum_verify(sb, first_group + i,
> > + desc->bg_block_bitmap_csum, bh[i],
> > + (EXT4_BLOCKS_PER_GROUP(sb) + 7) /
> > + 8)) {
> > + ext4_unlock_group(sb, first_group + i);
> > + ext4_error(sb, "Corrupt block bitmap, group = %u",
> > + first_group + i);
> > + goto out;
> > + }
> > + ext4_unlock_group(sb, first_group + i);
> > + set_buffer_verified(bh[i]);
> > + }
>
> Since this is CPU intensive, it might make sense to start computing the
> block bitmap checksums as soon as the buffer is uptodate, instead of
> waiting for all of the buffers to be read and _then_ doing the checksums.
>
> Even better might be to do move all of the above code to do the checksum
> to be in a new the b_end_io callback, so that it can start as soon as each
> buffer is read from disk, to maximize CPU and IO overlap, like:
Good suggestion. I'll put it into the next rev.
--D
> struct ext4_csum_data {
> struct superblock *cd_sb;
> ext4_group_t cd_group;
> };
>
> static void ext4_end_buffered_read_sync_csum(struct buffer_head *bh,
> int uptodate)
> {
> struct superblock *sb = (struct ext4_csum_data *)(bh->b_private)->cd_sb;
> ext4_group_t group = (struct ext4_csum_data *)(bh->b_private)->cd_group;
>
> end_buffered_read_sync(bh, uptodate);
>
> if (uptodate) {
> struct ext4_group_desc *desc;
>
>
> desc = ext4_get_group_desc(sb, group, NULL);
> if (!desc)
> return;
>
> ext4_lock_group(sb, group);
> if (ext4_valid_block_bitmap(sb, desc, group, bh) &&
> ext4_bitmap_csum_verify(sb, group,
> desc->bg_block_bitmap_csum, bh,
> (EXT4_BLOCKS_PER_GROUP(sb) + 7) / 8))
> set_buffer_verified(bh);
>
> ext4_unlock_group(rcd->rcd_sb, rcd->rcd_group);
> }
> }
>
> Then later in the code can just check buffer_verified() in the caller:
>
> ext4_read_block_bitmap()
> {
> /* read all groups the page covers into the cache */
> for (i = 0; i < groups_per_page; i++) {
> :
> :
> set_bitmap_uptodate(bh[i]);
> ecd[i].cd_sb = sb;
> ecd[i].cd_group = first_group + i;
> bh[i]->b_end_io = ext4_end_buffer_read_sync_csum;
> submit_bh(READ, bh[i]);
> mb_debug(1, "read bitmap for group %u\n", first_group + i);
> }
>
> err = 0;
> /* always wait for I/O completion before returning */
> for (i = 0; i < groups_per_page; i++) {
> if (bh[i]) {
> wait_on_buffer(bh[i]);
> if (!buffer_uptodate(bh[i]) ||
> !buffer_verified(bh[i]))
> err = -EIO;
> }
> }
>
>
> > err = 0;
> > first_block = page->index * blocks_per_page;
> > for (i = 0; i < blocks_per_page; i++) {
> > @@ -2829,6 +2856,9 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
> > }
> > len = ext4_free_blks_count(sb, gdp) - ac->ac_b_ex.fe_len;
> > ext4_free_blks_set(sb, gdp, len);
> > + ext4_bitmap_csum_set(sb, ac->ac_b_ex.fe_group,
> > + &gdp->bg_block_bitmap_csum, bitmap_bh,
> > + (EXT4_BLOCKS_PER_GROUP(sb) + 7) / 8);
> > gdp->bg_checksum = ext4_group_desc_csum(sbi, ac->ac_b_ex.fe_group, gdp);
> >
> > ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
> > @@ -4638,6 +4668,8 @@ do_more:
> >
> > ret = ext4_free_blks_count(sb, gdp) + count;
> > ext4_free_blks_set(sb, gdp, ret);
> > + ext4_bitmap_csum_set(sb, block_group, &gdp->bg_block_bitmap_csum,
> > + bitmap_bh, (EXT4_BLOCKS_PER_GROUP(sb) + 7) / 8);
> > gdp->bg_checksum = ext4_group_desc_csum(sbi, block_group, gdp);
> > ext4_unlock_group(sb, block_group);
> > percpu_counter_add(&sbi->s_freeblocks_counter, count);
> > @@ -4780,6 +4812,8 @@ int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
> > mb_free_blocks(NULL, &e4b, bit, count);
> > blk_free_count = blocks_freed + ext4_free_blks_count(sb, desc);
> > ext4_free_blks_set(sb, desc, blk_free_count);
> > + ext4_bitmap_csum_set(sb, block_group, &desc->bg_block_bitmap_csum,
> > + bitmap_bh, (EXT4_BLOCKS_PER_GROUP(sb) + 7) / 8);
> > desc->bg_checksum = ext4_group_desc_csum(sbi, block_group, desc);
> > ext4_unlock_group(sb, block_group);
> > percpu_counter_add(&sbi->s_freeblocks_counter, blocks_freed);
> >
>
--
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