linux-kernel - Re: [PATCH v4] page_io: zswap: do not crash the kernel on decompression failure

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Message-ID: <aCJF74ILruXJOAkQ@casper.infradead.org>
Date: Mon, 12 May 2025 20:03:11 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Nhat Pham <nphamcs@...il.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, yosryahmed@...gle.com,
	yosry.ahmed@...ux.dev, chengming.zhou@...ux.dev, linux-mm@...ck.org,
	kernel-team@...a.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] page_io: zswap: do not crash the kernel on
 decompression failure

On Thu, Mar 06, 2025 at 12:50:10PM -0800, Nhat Pham wrote:
> -static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
> +static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio)

Hm, why do it this way?  I had it as:

-static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
+static int zswap_decompress(struct zswap_entry *entry, struct folio *folio)
...
+       err = crypto_acomp_decompress(acomp_ctx->req);
+       err = crypto_wait_req(err, &acomp_ctx->wait);
+       if (!err && acomp_ctx->req->dlen != PAGE_SIZE)
+               err = -EIO;

which allows us to return something more meaningful than -EIO.  Or is
doing that a bad idea and we should squash all decompression failures
to EIO?

(also i really dislike the chained approach:

        decomp_ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);

that's much harder to understand than the two lines i have above)