Re: [PATCH 1/4] xfs: shutdown if block allocation overruns tx reservation

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Feb 05, 2018 at 12:45:58PM -0500, Brian Foster wrote:
> The ->t_blk_res_used field tracks how many blocks have been used in
> the current transaction. This should never exceed the block
> reservation (->t_blk_res) for a particular transaction. We currently
> assert this condition in the transaction block accounting code, but
> otherwise take no additional action should this situation occur.
> 
> The overrun generally has no effect if space ends up being available
> and the associated transaction commits. If the transaction is
> duplicated, however, the current block usage is used to determine
> the remaining block reservation to be transferred to the new
> transaction. If usage exceeds reservation, this calculation
> underflows and creates a transaction with an invalid and excessive
> reservation. When the second transaction commits, the release of
> unused blocks corrupts the in-core free space counters. With lazy
> superblock accounting enabled, this inconsistency eventually
> trickles to the on-disk superblock and corrupts the filesystem.
> 
> Replace the transaction block usage accounting assert with an
> explicit overrun check. If the transaction overruns the reservation,
> shutdown the filesystem immediately to prevent corruption. Add a new
> assert to xfs_trans_dup() to catch any callers that might induce
> this invalid state in the future.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D