linux-kernel - Re: [PATCH v1] mm/hwpoison: convert TTU_IGNORE_HWPOISON to TTU

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Message-ID: <Y/TIq05CjrMyg7f0@casper.infradead.org>
Date:   Tue, 21 Feb 2023 13:35:39 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm/hwpoison: convert TTU_IGNORE_HWPOISON to
 TTU_HWPOISON

On Tue, Feb 21, 2023 at 05:59:05PM +0900, Naoya Horiguchi wrote:
> After a memory error happens on a clean folio, a process unexpectedly
> receives SIGBUS when it accesses to the error page.  This SIGBUS killing
> is pointless and simply degrades the level of RAS of the system, because
> the clean folio can be dropped without any data lost on memory error
> handling as we do for a clean pagecache.
> 
> When memory_failure() is called on a clean folio, try_to_unmap() is called
> twice (one from split_huge_page() and one from hwpoison_user_mappings()).
> The root cause of the issue is that pte conversion to hwpoisoned entry is
> now done in the first call of try_to_unmap() because PageHWPoison is already
> set at this point, while it's actually expected to be done in the second
> call.  This behavior disturbs the error handling operation like removing
> pagecache, which results in the malfunction described above.
> 
> So convert TTU_IGNORE_HWPOISON into TTU_HWPOISON and set TTU_HWPOISON only
> when we really intend to convert pte to hwpoison entry.  This can prevent
> other callers of try_to_unmap() from accidentally converting to hwpoison
> entries.
> 
> Fixes: a42634a6c07d ("readahead: Use a folio in read_pages()")

How did you choose this Fixes tag?