Re: [PATCH v3] btrfs: volumes: Increase bioc pointer check

[Qu Wenruo]

On 2022/10/26 09:36, Li zeming wrote:
> The __GFP_NOFAIL flag will cause memory to be allocated an infinite
> number of times until the allocation is successful, but it is best to
> use it only for very necessary code, and try not to use it.
>
> The alloc_btrfs_io_context function looks a little closer to normal
> (excuse my analysis), but I think we can remove __GFP_NOFAIL from it and
> add a bioc pointer allocation check that returns NULL if the allocation
> fails.
>
> Signed-off-by: Li zeming <zeming@xxxxxxxxxxxx>
> ---
>   v2: Add annotation vocabulary modify, remove __GFP_NOFAIL flag.
>   v3: Modifying the Description.
>
>   fs/btrfs/volumes.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 064ab2a79c80..b8d901f58995 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -5891,7 +5891,9 @@ static struct btrfs_io_context *alloc_btrfs_io_context(struct btrfs_fs_info *fs_
>   		 * and the stripes.
>   		 */
>   		sizeof(u64) * (total_stripes),
> -		GFP_NOFS|__GFP_NOFAIL);
> +		GFP_NOFS);
> +	if (!bioc)
> +		return NULL;
>
>   	atomic_set(&bioc->error, 0);
>   	refcount_set(&bioc->refs, 1);
> @@ -6071,7 +6073,7 @@ struct btrfs_discard_stripe *btrfs_map_discard(struct btrfs_fs_info *fs_info,
>    * array of stripes.
>    * For READ, it also needs to be supported using the same mirror number.
>    *
> - * If the requested block is not left of the left cursor, EIO is returned. This
> + * If the requested block is not left of the left cursor, EIO should be returned. This

Is there any need for this change?

I don't think your patch has even touched the call chain of
get_extra_mirror_from_replace().

Thanks,
Qu
>    * can happen because btrfs_num_copies() returns one more in the dev-replace
>    * case.
>    */