linux-kernel - Re: [PATCH v3 1/3] mm/swapfile: unuse_pte can map random data if swap read fails

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Date:   Thu, 12 May 2022 17:42:47 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     HORIGUCHI NAOYA (堀口 直也) <naoya.horiguchi@....com>,
        "willy@...radead.org" <willy@...radead.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "neilb@...e.de" <neilb@...e.de>,
        "david@...hat.com" <david@...hat.com>,
        "apopple@...dia.com" <apopple@...dia.com>,
        "surenb@...gle.com" <surenb@...gle.com>,
        "minchan@...nel.org" <minchan@...nel.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] mm/swapfile: unuse_pte can map random data if
 swap read fails

On Tue, 10 May 2022 14:58:05 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:

> >> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> >> Acked-by: David Hildenbrand <david@...hat.com>
> > 
> > When I reproduced the issue (generated read error with dm-dust), I saw
> > infinite loop in the while loop in shmem_unuse_inode() (and this happens
> > even with this patch). I confirmed that shmem_swapin_page() returns -EIO,
> > but shmem_unuse_swap_entries() does not return the error to the callers,
> > so the while loop in shmem_unuse_inode() seems not break.
> > 
> 
> Many thanks for your report! I didn't test the shmem case because I saw -EIO
> is returned. So I just focus on the normal page case. Sorry about it. :(
> 
> > So maybe you need more code around shmem_unuse_inode() to handle the error?
> 
> I will try to reproduce it and come up a fixup patch asap! And if you like, you
> can kindly solve this issue too. ;)

Seems that this patch didn't cause the infinite loop, so as far as I
can tell it is good to be merged up.  But the problem it solves isn't
urgent and fixing that infinite loop might impact this change so I
think I'll drop this version.