Re: [PATCH 2/4] fsx: fix infinite/too long loops when generating ranges for clone operations

[Brian Foster <bfoster@redhat.com>]

On Wed, Apr 08, 2020 at 11:36:04AM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> While running generic/457 I've had fsx taking a lot of CPU time and not
> making any progress for over an hour. Attaching gdb to the fsx process
> revealed that fsx was in the loop that generates the ranges for a clone
> operation, in particular the loop seemed to never end because the range
> defined by 'offset2' kept overlapping with the range defined by 'offset'.
> So far this happened two times in one of my test VMs with generic/457.
> 
> Fix this by breaking out of the loop after trying 30 times, like we
> currently do for dedupe operations, which results in logging the operation
> as skipped.
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---

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

>  ltp/fsx.c | 28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/ltp/fsx.c b/ltp/fsx.c
> index fa383c94..5949ebf0 100644
> --- a/ltp/fsx.c
> +++ b/ltp/fsx.c
> @@ -2004,16 +2004,24 @@ test(void)
>  			keep_size = random() % 2;
>  		break;
>  	case OP_CLONE_RANGE:
> -		TRIM_OFF_LEN(offset, size, file_size);
> -		offset = offset & ~(block_size - 1);
> -		size = size & ~(block_size - 1);
> -		do {
> -			offset2 = random();
> -			TRIM_OFF(offset2, maxfilelen);
> -			offset2 = offset2 & ~(block_size - 1);
> -		} while (range_overlaps(offset, offset2, size) ||
> -			 offset2 + size > maxfilelen);
> -		break;
> +		{
> +			int tries = 0;
> +
> +			TRIM_OFF_LEN(offset, size, file_size);
> +			offset = offset & ~(block_size - 1);
> +			size = size & ~(block_size - 1);
> +			do {
> +				if (tries++ >= 30) {
> +					size = 0;
> +					break;
> +				}
> +				offset2 = random();
> +				TRIM_OFF(offset2, maxfilelen);
> +				offset2 = offset2 & ~(block_size - 1);
> +			} while (range_overlaps(offset, offset2, size) ||
> +				 offset2 + size > maxfilelen);
> +			break;
> +		}
>  	case OP_DEDUPE_RANGE:
>  		{
>  			int tries = 0;
> -- 
> 2.11.0
>