linux-kernel - Re: [PATCH v2] btrfs: volumes: Increase bioc pointer check

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Date:   Tue, 25 Oct 2022 19:17:10 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Li zeming <zeming@...china.com>, clm@...com, josef@...icpanda.com,
        dsterba@...e.com, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] btrfs: volumes: Increase bioc pointer check



On 2022/10/25 18:52, Li zeming wrote:
> This patch has the following changes:
> 1. Modify "is returned" in the comments to "should be returned".
> 2. Remove the __GFP_NOFAIL flag from the kzalloc function, which returns
> NULL if kzalloc fails to allocate memory for bioc.

Firstly this part should be in change log, not commit message.

You can just do a search in the mail list and see how we handle patches
with newer versions.

Secondly, you didn't mention why we can remove the __GFP_NOFAIL flag at all.

The commit message should look like this instead:

```
Currently we allocate memory for btrfs_io_context using
(GFP_NOFS|__GFP_NOFAIL) in alloc_btrfs_io_context().

But there is nothing special for that function to require NOFAIL flag.

Furthermore the only caller of alloc_btrfs_io_context() is already
handling the ENOMEM error properly.

Thus we can safely remove the __GFP_NOFAIL flag, and handle allocation
failure properly.
```
>
> Reviewed-by: Qu Wenruo <wqu@...e.com>

I'd say, please don't add my tag until everything is fine.
I did a wrong expectation.

Thanks,
Qu

> Signed-off-by: Li zeming <zeming@...china.com>
> ---
>   v2: Add annotation vocabulary modify, remove __GFP_NOFAIL flag.
>
>   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
>    * can happen because btrfs_num_copies() returns one more in the dev-replace
>    * case.
>    */