On 1/30/17 6:23 PM, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
>
> We use di_format and if_flags to decide whether we're grabbing the ilock
> in btree mode (btree extents not loaded) or shared mode (anything else),
> but the state of those fields can be changed by other threads that are
> also trying to load the btree extents -- IFEXTENTS gets set before the
> _bmap_read_extents call and cleared if it fails. Therefore, once we've
> grabbed the shared ilock we have to re-check the fields to see if we
> actually need to upgrade to the exclusive ilock in order to try loading
> the extents.
>
> Without this patch, we trigger ilock assert failures when a bunch of
> threads try to access a btree format directory with a corrupt bmbt root
> and corrupt the incore data structures, leading to a crash.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
I'm a little surprised this hasn't been hit before, TBH.
Seems right -
Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
> fs/xfs/xfs_inode.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
>
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index de32f0f..7d7206c 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -125,6 +125,18 @@ xfs_ilock_data_map_shared(
> (ip->i_df.if_flags & XFS_IFEXTENTS) == 0)
> lock_mode = XFS_ILOCK_EXCL;
> xfs_ilock(ip, lock_mode);
> + /*
> + * We can change if_flags under ilock if we try to read the
> + * extents and fail. Since we hadn't grabbed the ilock at check
> + * time, we have to re-check and upgrade the lock now.
> + */
> + if (lock_mode == XFS_ILOCK_SHARED &&
> + ip->i_d.di_format == XFS_DINODE_FMT_BTREE &&
> + (ip->i_df.if_flags & XFS_IFEXTENTS) == 0) {
> + xfs_iunlock(ip, lock_mode);
> + lock_mode = XFS_ILOCK_EXCL;
> + xfs_ilock(ip, lock_mode);
> + }
> return lock_mode;
> }
>
>
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