linux-kernel - Re: [PATCH v4 11/11] md/md-llbitmap: introduce new lockless bitmap

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Message-ID: <f282237e-be12-b178-0e25-3a73bd20d77c@huaweicloud.com>
Date: Fri, 1 Aug 2025 10:00:41 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Yu Kuai <yukuai@...nel.org>, corbet@....net, agk@...hat.co,
 snitzer@...nel.org, mpatocka@...hat.com, hch@....de, song@...nel.org,
 hare@...e.de
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 dm-devel@...ts.linux.dev, linux-raid@...r.kernel.org, yangerkun@...wei.com,
 yi.zhang@...wei.com, johnny.chenyi@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v4 11/11] md/md-llbitmap: introduce new lockless bitmap

Hi,

在 2025/07/22 1:15, Yu Kuai 写道:
> +static int llbitmap_read_sb(struct llbitmap *llbitmap)
> +{
> +	struct mddev *mddev = llbitmap->mddev;
> +	unsigned long daemon_sleep;
> +	unsigned long chunksize;
> +	unsigned long events;
> +	struct page *sb_page;
> +	bitmap_super_t *sb;
> +	int ret = -EINVAL;
> +
> +	if (!mddev->bitmap_info.offset) {
> +		pr_err("md/llbitmap: %s: no super block found", mdname(mddev));
> +		return -EINVAL;
> +	}
> +
> +	sb_page = llbitmap_read_page(llbitmap, 0);
> +	if (IS_ERR(sb_page)) {
> +		pr_err("md/llbitmap: %s: read super block failed",
> +		       mdname(mddev));

There should return -EIO directly here.
> +		ret = -EIO;
> +		goto out;

And the out tag can be removed.

Thanks,
Kuai

> +	}
> +
> +	sb = kmap_local_page(sb_page);
> +	if (sb->magic != cpu_to_le32(BITMAP_MAGIC)) {
> +		pr_err("md/llbitmap: %s: invalid super block magic number",
> +		       mdname(mddev));
> +		goto out_put_page;
> +	}
> +
> +	if (sb->version != cpu_to_le32(BITMAP_MAJOR_LOCKLESS)) {
> +		pr_err("md/llbitmap: %s: invalid super block version",
> +		       mdname(mddev));
> +		goto out_put_page;
> +	}
> +
> +	if (memcmp(sb->uuid, mddev->uuid, 16)) {
> +		pr_err("md/llbitmap: %s: bitmap superblock UUID mismatch\n",
> +		       mdname(mddev));
> +		goto out_put_page;
> +	}
> +
> +	if (mddev->bitmap_info.space == 0) {
> +		int room = le32_to_cpu(sb->sectors_reserved);
> +
> +		if (room)
> +			mddev->bitmap_info.space = room;
> +		else
> +			mddev->bitmap_info.space = mddev->bitmap_info.default_space;
> +	}
> +	llbitmap->flags = le32_to_cpu(sb->state);
> +	if (test_and_clear_bit(BITMAP_FIRST_USE, &llbitmap->flags)) {
> +		ret = llbitmap_init(llbitmap);
> +		goto out_put_page;
> +	}
> +
> +	chunksize = le32_to_cpu(sb->chunksize);
> +	if (!is_power_of_2(chunksize)) {
> +		pr_err("md/llbitmap: %s: chunksize not a power of 2",
> +		       mdname(mddev));
> +		goto out_put_page;
> +	}
> +
> +	if (chunksize < DIV_ROUND_UP(mddev->resync_max_sectors,
> +				     mddev->bitmap_info.space << SECTOR_SHIFT)) {
> +		pr_err("md/llbitmap: %s: chunksize too small %lu < %llu / %lu",
> +		       mdname(mddev), chunksize, mddev->resync_max_sectors,
> +		       mddev->bitmap_info.space);
> +		goto out_put_page;
> +	}
> +
> +	daemon_sleep = le32_to_cpu(sb->daemon_sleep);
> +	if (daemon_sleep < 1 || daemon_sleep > MAX_SCHEDULE_TIMEOUT / HZ) {
> +		pr_err("md/llbitmap: %s: daemon sleep %lu period out of range",
> +		       mdname(mddev), daemon_sleep);
> +		goto out_put_page;
> +	}
> +
> +	events = le64_to_cpu(sb->events);
> +	if (events < mddev->events) {
> +		pr_warn("md/llbitmap :%s: bitmap file is out of date (%lu < %llu) -- forcing full recovery",
> +			mdname(mddev), events, mddev->events);
> +		set_bit(BITMAP_STALE, &llbitmap->flags);
> +	}
> +
> +	sb->sync_size = cpu_to_le64(mddev->resync_max_sectors);
> +	mddev->bitmap_info.chunksize = chunksize;
> +	mddev->bitmap_info.daemon_sleep = daemon_sleep;
> +
> +	llbitmap->barrier_idle = DEFAULT_BARRIER_IDLE;
> +	llbitmap->chunksize = chunksize;
> +	llbitmap->chunks = DIV_ROUND_UP(mddev->resync_max_sectors, chunksize);
> +	llbitmap->chunkshift = ffz(~chunksize);
> +	ret = llbitmap_cache_pages(llbitmap);
> +
> +out_put_page:
> +	__free_page(sb_page);
> +out:
> +	kunmap_local(sb);
> +	return ret;
> +}