linux-kernel - Re: [PATCH v2] zswap: do not crash the kernel on decompression failure

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Message-ID: <20250227043141.GB110982@cmpxchg.org>
Date: Wed, 26 Feb 2025 23:31:41 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Nhat Pham <nphamcs@...il.com>, akpm@...ux-foundation.org,
	chengming.zhou@...ux.dev, linux-mm@...ck.org, kernel-team@...a.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] zswap: do not crash the kernel on decompression
 failure

On Thu, Feb 27, 2025 at 01:19:31AM +0000, Yosry Ahmed wrote:
> On Wed, Feb 26, 2025 at 04:14:45PM -0800, Nhat Pham wrote:
> >  	if (WARN_ON_ONCE(folio_test_large(folio)))
> >  		return true;
> >  
> > +	entry = xa_load(tree, offset);
> > +	if (!entry)
> > +		return false;
> > +
> 
> A small comment here pointing out that we are deliberatly not setting
> uptodate because of the failure may make things more obvious, or do you
> think that's not needed?
>
> > +	if (!zswap_decompress(entry, folio))
> > +		return true;

How about an actual -ev and have this in swap_read_folio():

        ret = zswap_load(folio);
        if (ret != -ENOENT) {
                folio_unlock(folio);
                goto finish;
        }

	read from swapfile...

Then in zswap_load(), move uptodate further up like this (I had
previously suggested this):

	if (!zswap_decompress(entry, folio))
		return -EIO;

	folio_mark_uptodate(folio);

and I think it would be clear, even without or just minimal comments.