linux-kernel - Re: [PATCHv3 1/4] zram: introduce writeback bio batching support

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Message-ID: <tencent_295C252FFDABBAEBA3088D5B72DCDE15EB05@qq.com>
Date: Tue, 18 Nov 2025 11:18:56 +0800
From: Yuwen Chen <ywen.chen@...mail.com>
To: senozhatsky@...omium.org
Cc: akpm@...ux-foundation.org,
	bgeffon@...gle.com,
	licayy@...look.com,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	minchan@...gle.com,
	minchan@...nel.org,
	richardycc@...gle.com,
	ywen.chen@...mail.com
Subject: Re: [PATCHv3 1/4] zram: introduce writeback bio batching support

On Mon, 17 Nov 2025 10:19:22 -0500, Sergey Senozhatsky wrote:
> +static int zram_writeback_complete(struct zram *zram, struct zram_wb_req *req)
> +{
> +	u32 index;
> +	int err;
> +
> +	index = req->pps->index;
> +	release_pp_slot(zram, req->pps);
> +	req->pps = NULL;
> +
> +	err = blk_status_to_errno(req->bio.bi_status);
> +	if (err) {
> +		/*
> +		 * Failed wb requests should not be accounted in wb_limit
> +		 * (if enabled).
> +		 */
> +		zram_account_writeback_rollback(zram);
In this place, the index may be leaked.

> +		return err;
> +	}
> +
> +	atomic64_inc(&zram->stats.bd_writes);
> +	zram_slot_lock(zram, index);
> +	/*
> +	 * We release slot lock during writeback so slot can change under us:
> +	 * slot_free() or slot_free() and zram_write_page(). In both cases
> +	 * slot loses ZRAM_PP_SLOT flag. No concurrent post-processing can
> +	 * set ZRAM_PP_SLOT on such slots until current post-processing
> +	 * finishes.
> +	 */
> +	if (!zram_test_flag(zram, index, ZRAM_PP_SLOT))
> +		goto out;
In this place, the index may be leaked.

> +
> +	zram_free_page(zram, index);
> +	zram_set_flag(zram, index, ZRAM_WB);
> +	zram_set_handle(zram, index, req->blk_idx);
> +	atomic64_inc(&zram->stats.pages_stored);
> +
> +out:
> +	zram_slot_unlock(zram, index);
> +	return 0;
> +}