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
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
WARNING: multiple messages have this Message-ID (diff)
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
next prev parent reply other threads:[~2016-05-18 9:21 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-17 7:42 [PATCH v1] mm: bad_page() checks bad_flags instead of page->flags for hwpoison page Naoya Horiguchi
2016-05-17 7:42 ` Naoya Horiguchi
2016-05-18 7:30 ` Vlastimil Babka
2016-05-18 7:30 ` Vlastimil Babka
2016-05-18 9:21 ` Mel Gorman [this message]
2016-05-18 9:21 ` Mel Gorman
2016-05-18 9:31 ` Vlastimil Babka
2016-05-18 9:31 ` Vlastimil Babka
2016-05-18 9:52 ` Mel Gorman
2016-05-18 9:52 ` Mel Gorman
2016-05-18 10:17 ` Naoya Horiguchi
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 10:09 ` Naoya Horiguchi
2016-05-18 14:03 ` Mel Gorman
2016-05-18 14:03 ` Mel Gorman
2016-05-20 14:27 ` Vlastimil Babka
2016-05-20 14:27 ` Vlastimil Babka
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160518092100.GB2527@techsingularity.net \
--to=mgorman@techsingularity.net \
--cc=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=n-horiguchi@ah.jp.nec.com \
--cc=nao.horiguchi@gmail.com \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.