Re: [PATCH 1/2] mm/migrate.c: Fix return code when migration fails

[Michal Hocko <mhocko@suse.com>]

On Mon 07-08-23 16:39:44, Alistair Popple wrote:
> When a page fails to migrate move_pages() returns the error code in a
> per-page array of status values. The function call itself is also
> supposed to return a summary error code indicating that a failure
> occurred.
> 
> This doesn't always happen. Instead success can be returned even
> though some pages failed to migrate. This is due to incorrectly
> returning the error code from store_status() rather than the code from
> add_page_for_migration. Fix this by only returning an error from
> store_status() if the store actually failed.

Error reporting by this syscall has been really far from
straightforward. Please read through a49bd4d71637 and the section "On a
side note". 
Is there any specific reason you are trying to address this now or is
this motivated by the code inspection?

> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move")
> ---
>  mm/migrate.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 24baad2571e3..bb3a37245e13 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2222,7 +2222,9 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>  		 * If the page is already on the target node (!err), store the
>  		 * node, otherwise, store the err.
>  		 */
> -		err = store_status(status, i, err ? : current_node, 1);
> +		err1 = store_status(status, i, err ? : current_node, 1);
> +		if (err1)
> +			err = err1;
>  		if (err)
>  			goto out_flush;
>  
> -- 
> 2.39.2

-- 
Michal Hocko
SUSE Labs