Re: [PATCH V2] raid1: ensure write behind bio has less than BIO_MAX_VECS sectors

[Guoqing Jiang <guoqing.jiang@linux.dev>]

Missed to cc Song and Christoph, now actually do it ...

On 8/18/21 3:37 PM, Guoqing Jiang wrote:
> From: Guoqing Jiang <jiangguoqing@kylinos.cn>
>
> We can't split write behind bio with more than BIO_MAX_VECS sectors,
> otherwise the below call trace was triggered because we could allocate
> oversized write behind bio later.
>
> [ 8.097936] bvec_alloc+0x90/0xc0
> [ 8.098934] bio_alloc_bioset+0x1b3/0x260
> [ 8.099959] raid1_make_request+0x9ce/0xc50 [raid1]
> [ 8.100988] ? __bio_clone_fast+0xa8/0xe0
> [ 8.102008] md_handle_request+0x158/0x1d0 [md_mod]
> [ 8.103050] md_submit_bio+0xcd/0x110 [md_mod]
> [ 8.104084] submit_bio_noacct+0x139/0x530
> [ 8.105127] submit_bio+0x78/0x1d0
> [ 8.106163] ext4_io_submit+0x48/0x60 [ext4]
> [ 8.107242] ext4_writepages+0x652/0x1170 [ext4]
> [ 8.108300] ? do_writepages+0x41/0x100
> [ 8.109338] ? __ext4_mark_inode_dirty+0x240/0x240 [ext4]
> [ 8.110406] do_writepages+0x41/0x100
> [ 8.111450] __filemap_fdatawrite_range+0xc5/0x100
> [ 8.112513] file_write_and_wait_range+0x61/0xb0
> [ 8.113564] ext4_sync_file+0x73/0x370 [ext4]
> [ 8.114607] __x64_sys_fsync+0x33/0x60
> [ 8.115635] do_syscall_64+0x33/0x40
> [ 8.116670] entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Thanks for the comment from Christoph.
>
> [1]. https://bugs.archlinux.org/task/70992
>
> Cc: Song Liu <song@kernel.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Reported-by: Jens Stutte <jens@chianterastutte.eu>
> Tested-by: Jens Stutte <jens@chianterastutte.eu>
> Signed-off-by: Guoqing Jiang <jiangguoqing@kylinos.cn>
> ---
> Hi Jens,
>
> Could you consider apply this to block tree? Since it depends
> on commit 018eca456c4b4dca56aaf1ec27f309c74d0fe246 in block
> tree for-next branch, otherwise lkp would complain about compile
> issue again.
>
> Thanks,
> Guoqing
>
> V2 change:
> 1. add checking for write-behind case and relevant comments from Christoph.
>
>   drivers/md/raid1.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 3c44c4bb40fc..e8c8e6bb0439 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -1329,6 +1329,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
>   	struct raid1_plug_cb *plug = NULL;
>   	int first_clone;
>   	int max_sectors;
> +	bool write_behind = false;
>   
>   	if (mddev_is_clustered(mddev) &&
>   	     md_cluster_ops->area_resyncing(mddev, WRITE,
> @@ -1381,6 +1382,10 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
>   	max_sectors = r1_bio->sectors;
>   	for (i = 0;  i < disks; i++) {
>   		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
> +
> +		if (test_bit(WriteMostly, &mirror->rdev->flags))
> +			write_behind = true;
> +
>   		if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
>   			atomic_inc(&rdev->nr_pending);
>   			blocked_rdev = rdev;
> @@ -1454,6 +1459,14 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
>   		goto retry_write;
>   	}
>   
> +	/*
> +	 * When using a bitmap, we may call alloc_behind_master_bio below.
> +	 * alloc_behind_master_bio allocates a copy of the data payload a page
> +	 * at a time and thus needs a new bio that can fit the whole payload
> +	 * this bio in page sized chunks.
> +	 */
> +	if (write_behind && bitmap)
> +		max_sectors = min_t(int, max_sectors, BIO_MAX_VECS * PAGE_SECTORS);
>   	if (max_sectors < bio_sectors(bio)) {
>   		struct bio *split = bio_split(bio, max_sectors,
>   					      GFP_NOIO, &conf->bio_split);