Re: [PATCH] ext4: make sure to revoke all the freeable blocks in ext4_free_blocks

Re: [PATCH] ext4: make sure to revoke all the freeable blocks in ext4_free_blocks

[Daeho Jeong]

It looks clearer. I will modify the condition as you mentioned.

Thank you for your review. :-)

[PATCH] ext4: make sure to revoke all the freeable blocks in ext4_free_blocks

[Daeho Jeong]

Now, ext4_free_blocks() doesn't revoke data blocks of per-file data
journalled inode and it can cause file data inconsistency problems.
Even though data blocks of per-file data journalled inode are already
forgotten by jbd2_journal_invalidatepage() in advance of invoking
ext4_free_blocks(), we still need to revoke the data blocks here.
Moreover some of the metadata blocks, which are not found by
sb_find_get_block(), are still needed to be revoked, but this is also
missing here.

Signed-off-by: Daeho Jeong <daeho.jeong@samsung.com>
---
 fs/ext4/mballoc.c |   29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 61eaf74..e40a2df 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4695,16 +4695,6 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 	}
 
 	/*
-	 * We need to make sure we don't reuse the freed block until
-	 * after the transaction is committed, which we can do by
-	 * treating the block as metadata, below.  We make an
-	 * exception if the inode is to be written in writeback mode
-	 * since writeback mode has weak data consistency guarantees.
-	 */
-	if (!ext4_should_writeback_data(inode))
-		flags |= EXT4_FREE_BLOCKS_METADATA;
-
-	/*
 	 * If the extent to be freed does not begin on a cluster
 	 * boundary, we need to deal with partial clusters at the
 	 * beginning and end of the extent.  Normally we will free
@@ -4738,17 +4728,26 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 
 	if (!bh && (flags & EXT4_FREE_BLOCKS_FORGET)) {
 		int i;
+		int is_metadata = flags & EXT4_FREE_BLOCKS_METADATA;
 
 		for (i = 0; i < count; i++) {
 			cond_resched();
-			bh = sb_find_get_block(inode->i_sb, block + i);
-			if (!bh)
-				continue;
-			ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
-				    inode, bh, block + i);
+			if (is_metadata)
+				bh = sb_find_get_block(inode->i_sb, block + i);
+			ext4_forget(handle, is_metadata, inode, bh, block + i);
 		}
 	}
 
+	/*
+	 * We need to make sure we don't reuse the freed block until
+	 * after the transaction is committed, which we can do by
+	 * treating the block as metadata, below.  We make an
+	 * exception if the inode is to be written in writeback mode
+	 * since writeback mode has weak data consistency guarantees.
+	 */
+	if (!ext4_should_writeback_data(inode))
+		flags |= EXT4_FREE_BLOCKS_METADATA;
+
 do_more:
 	overflow = 0;
 	ext4_get_group_no_and_offset(sb, block, &block_group, &bit);
-- 
1.7.9.5

Re: [PATCH] ext4: make sure to revoke all the freeable blocks in ext4_free_blocks

[Jan Kara]

On Wed 16-12-15 09:20:43, Daeho Jeong wrote:
> Now, ext4_free_blocks() doesn't revoke data blocks of per-file data
> journalled inode and it can cause file data inconsistency problems.
> Even though data blocks of per-file data journalled inode are already
> forgotten by jbd2_journal_invalidatepage() in advance of invoking
> ext4_free_blocks(), we still need to revoke the data blocks here.
> Moreover some of the metadata blocks, which are not found by
> sb_find_get_block(), are still needed to be revoked, but this is also
> missing here.

Thanks for looking into the issue! Just one small nit below.

> Signed-off-by: Daeho Jeong <daeho.jeong@samsung.com>
> ---
>  fs/ext4/mballoc.c |   29 ++++++++++++++---------------
>  1 file changed, 14 insertions(+), 15 deletions(-)
...

> +	/*
> +	 * We need to make sure we don't reuse the freed block until
> +	 * after the transaction is committed, which we can do by
> +	 * treating the block as metadata, below.  We make an
> +	 * exception if the inode is to be written in writeback mode
> +	 * since writeback mode has weak data consistency guarantees.
> +	 */
> +	if (!ext4_should_writeback_data(inode))
> +		flags |= EXT4_FREE_BLOCKS_METADATA;
> +

I think it would be clearer what's going on if your just modified the
condition checking whether EFD entry needs to be created. Like:

-	if ((flags & EXT4_FREE_BLOCKS_METADATA) && ext4_handle_valid(handle)) {
+	/*
+	 * We need to make sure we don't reuse the freed block until after the
+	 * transaction is committed. We make an exception if the inode is to be
+	 * written in writeback mode since writeback mode has weak data
+	 * consistency guarantees.
+	 */
+	if (ext4_handle_valid(handle) &&
+	    ((flags & EXT4_FREE_BLOCKS_METADATA) ||
+	     !ext4_should_writeback_data(inode))) {
		struct ext4_free_data *new_entry;
		/*
-		 * blocks being freed are metadata. these blocks shouldn't
-		 * be used until this transaction is committed
-		 *
		 * We use __GFP_NOFAIL because ext4_free_blocks() is not
		 * allowed
		 * to fail.

Otherwise the patch looks fine so after changing this feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR