Re: [PATCH] xfs: allow parent directory scans to be interrupted with fatal signals

[Brian Foster <bfoster@redhat.com>]

On Tue, Nov 26, 2019 at 08:15:17AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Allow a fatal signal to interrupt us when we're scanning a directory to
> verify a parent pointer.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/scrub/parent.c |   25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/scrub/parent.c b/fs/xfs/scrub/parent.c
> index 17100a83e23e..5705adc43a75 100644
> --- a/fs/xfs/scrub/parent.c
> +++ b/fs/xfs/scrub/parent.c
> @@ -32,8 +32,10 @@ xchk_setup_parent(
>  
>  struct xchk_parent_ctx {
>  	struct dir_context	dc;
> +	struct xfs_scrub	*sc;
>  	xfs_ino_t		ino;
>  	xfs_nlink_t		nlink;
> +	bool			cancelled;
>  };
>  
>  /* Look for a single entry in a directory pointing to an inode. */
> @@ -47,11 +49,21 @@ xchk_parent_actor(
>  	unsigned		type)
>  {
>  	struct xchk_parent_ctx	*spc;
> +	int			error = 0;
>  
>  	spc = container_of(dc, struct xchk_parent_ctx, dc);
>  	if (spc->ino == ino)
>  		spc->nlink++;
> -	return 0;
> +
> +	/*
> +	 * If we're facing a fatal signal, bail out.  Store the cancellation
> +	 * status separately because the VFS readdir code squashes error codes
> +	 * into short directory reads.
> +	 */
> +	if (xchk_should_terminate(spc->sc, &error))
> +		spc->cancelled = true;
> +
> +	return error;
>  }
>  
>  /* Count the number of dentries in the parent dir that point to this inode. */
> @@ -62,10 +74,9 @@ xchk_parent_count_parent_dentries(
>  	xfs_nlink_t		*nlink)
>  {
>  	struct xchk_parent_ctx	spc = {
> -		.dc.actor = xchk_parent_actor,
> -		.dc.pos = 0,
> -		.ino = sc->ip->i_ino,
> -		.nlink = 0,
> +		.dc.actor	= xchk_parent_actor,
> +		.ino		= sc->ip->i_ino,
> +		.sc		= sc,
>  	};
>  	size_t			bufsize;
>  	loff_t			oldpos;
> @@ -97,6 +108,10 @@ xchk_parent_count_parent_dentries(
>  		error = xfs_readdir(sc->tp, parent, &spc.dc, bufsize);
>  		if (error)
>  			goto out;
> +		if (spc.cancelled) {
> +			error = -EAGAIN;
> +			goto out;
> +		}
>  		if (oldpos == spc.dc.pos)
>  			break;
>  		oldpos = spc.dc.pos;
>