linux-kernel - Re: [PATCH 3/8][next] xfs: Avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <20250224191209.GZ21808@frogsfrogsfrogs>
Date: Mon, 24 Feb 2025 11:12:09 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Carlos Maiolino <cem@...nel.org>, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 3/8][next] xfs: Avoid -Wflex-array-member-not-at-end
 warnings

On Mon, Feb 24, 2025 at 08:27:44PM +1030, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Change the type of the middle struct members currently causing trouble
> from `struct bio` to `struct bio_hdr`.
> 
> We also use `container_of()` whenever we need to retrieve a pointer to
> the flexible structure `struct bio`, through which we can access the
> flexible-array member in it, if necessary.
> 
> With these changes fix 27 of the following warnings:
> 
> fs/xfs/xfs_log_priv.h:208:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  fs/xfs/xfs_log.c      | 15 +++++++++------
>  fs/xfs/xfs_log_priv.h |  2 +-
>  2 files changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index f8851ff835de..7e8b71f64a46 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -1245,7 +1245,7 @@ xlog_ioend_work(
>  	}
>  
>  	xlog_state_done_syncing(iclog);
> -	bio_uninit(&iclog->ic_bio);
> +	bio_uninit(container_of(&iclog->ic_bio, struct bio, __hdr));
>  
>  	/*
>  	 * Drop the lock to signal that we are done. Nothing references the
> @@ -1663,7 +1663,8 @@ xlog_write_iclog(
>  	 * writeback throttle from throttling log writes behind background
>  	 * metadata writeback and causing priority inversions.
>  	 */
> -	bio_init(&iclog->ic_bio, log->l_targ->bt_bdev, iclog->ic_bvec,
> +	bio_init(container_of(&iclog->ic_bio, struct bio, __hdr),
> +		 log->l_targ->bt_bdev, iclog->ic_bvec,
>  		 howmany(count, PAGE_SIZE),
>  		 REQ_OP_WRITE | REQ_META | REQ_SYNC | REQ_IDLE);
>  	iclog->ic_bio.bi_iter.bi_sector = log->l_logBBstart + bno;
> @@ -1692,7 +1693,8 @@ xlog_write_iclog(
>  
>  	iclog->ic_flags &= ~(XLOG_ICL_NEED_FLUSH | XLOG_ICL_NEED_FUA);
>  
> -	if (xlog_map_iclog_data(&iclog->ic_bio, iclog->ic_data, count))
> +	if (xlog_map_iclog_data(container_of(&iclog->ic_bio, struct bio, __hdr),
> +				iclog->ic_data, count))
>  		goto shutdown;
>  
>  	if (is_vmalloc_addr(iclog->ic_data))
> @@ -1705,16 +1707,17 @@ xlog_write_iclog(
>  	if (bno + BTOBB(count) > log->l_logBBsize) {
>  		struct bio *split;
>  
> -		split = bio_split(&iclog->ic_bio, log->l_logBBsize - bno,
> +		split = bio_split(container_of(&iclog->ic_bio, struct bio, __hdr),
> +				  log->l_logBBsize - bno,
>  				  GFP_NOIO, &fs_bio_set);
> -		bio_chain(split, &iclog->ic_bio);
> +		bio_chain(split, container_of(&iclog->ic_bio, struct bio, __hdr));
>  		submit_bio(split);
>  
>  		/* restart at logical offset zero for the remainder */
>  		iclog->ic_bio.bi_iter.bi_sector = log->l_logBBstart;
>  	}
>  
> -	submit_bio(&iclog->ic_bio);
> +	submit_bio(container_of(&iclog->ic_bio, struct bio, __hdr));
>  	return;
>  shutdown:
>  	xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index f3d78869e5e5..32abc48aef24 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -205,7 +205,7 @@ typedef struct xlog_in_core {
>  #endif
>  	struct semaphore	ic_sema;
>  	struct work_struct	ic_end_io_work;
> -	struct bio		ic_bio;
> +	struct bio_hdr		ic_bio;

What struct is this?

$ git grep 'struct bio_hdr' include/
$

(Please always send the core code change patches to the xfs list.)

--D

>  	struct bio_vec		ic_bvec[];
>  } xlog_in_core_t;
>  
> -- 
> 2.43.0
> 
>