From: Mel Gorman <mgorman@techsingularity.net>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Naoya Horiguchi <nao.horiguchi@gmail.com>
Subject: Re: [PATCH v1] mm: bad_page() checks bad_flags instead of page->flags for hwpoison page
Date: Wed, 18 May 2016 10:21:01 +0100 [thread overview]
Message-ID: <20160518092100.GB2527@techsingularity.net> (raw)
In-Reply-To: <1463470975-29972-1-git-send-email-n-horiguchi@ah.jp.nec.com>
On Tue, May 17, 2016 at 04:42:55PM +0900, Naoya Horiguchi wrote:
> There's a race window between checking page->flags and unpoisoning, which
> taints kernel with "BUG: Bad page state". That's overkill. It's safer to
> use bad_flags to detect hwpoisoned page.
>
I'm not quite getting this one. Minimally, instead of = __PG_HWPOISON, it
should have been (bad_flags & __PG_POISON). As Vlastimil already pointed
out, __PG_HWPOISON can be 0. What I'm not getting is why this fixes the
race. The current race is
1. Check poison, set bad_flags
2. poison clears in parallel
3. Check page->flag state in bad_page and trigger warning
The code changes it to
1. Check poison, set bad_flags
2. poison clears in parallel
3. Check bad_flags and trigger warning
There is warning either way. What did I miss?
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2016-05-18 9:21 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-17 7:42 Naoya Horiguchi
2016-05-18 7:30 ` Vlastimil Babka
2016-05-18 9:21 ` Mel Gorman [this message]
2016-05-18 9:31 ` Vlastimil Babka
2016-05-18 9:52 ` Mel Gorman
2016-05-18 10:17 ` Naoya Horiguchi
2016-05-18 10:09 ` [PATCH v2] mm: check_new_page_bad() directly returns in __PG_HWPOISON case Naoya Horiguchi
2016-05-18 14:03 ` Mel Gorman
2016-05-20 14:27 ` Vlastimil Babka
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