From: Minchan Kim <minchan@kernel.org>
To: Namhyung Kim <namhyung.kim@lge.com>
Cc: Minchan Kim <minchan@kernel.org>,
Christoph Lameter <cl@linux-foundation.org>,
Pekka Enberg <penberg@kernel.org>, Matt Mackall <mpm@selenic.com>,
Namhyung Kim <namhyung@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] slub: set PG_slab on all of slab pages
Date: Mon, 5 Mar 2012 19:59:18 +0900 [thread overview]
Message-ID: <20120305105918.GA13252@barrios> (raw)
In-Reply-To: <4F547C90.4040007@lge.com>
On Mon, Mar 05, 2012 at 05:42:56PM +0900, Namhyung Kim wrote:
> 2012-03-04 7:34 PM, Minchan Kim wrote:
> >Hi Namhyung,
> >
>
> Hi Minchan,
> glad to see you here again :)
Thanks!
>
>
> >On Wed, Feb 29, 2012 at 05:54:34PM +0900, Namhyung Kim wrote:
> >>Unlike SLAB, SLUB doesn't set PG_slab on tail pages, so if a user would
> >>call free_pages() incorrectly on a object in a tail page, she will get
> >>i confused with the undefined result. Setting the flag would help her by
> >>emitting a warning on bad_page() in such a case.
> >>
> >>Reported-by: Sangseok Lee <sangseok.lee@lge.com>
> >>Signed-off-by: Namhyung Kim <namhyung.kim@lge.com>
> >
> >I read this thread and I feel the we don't reach right point.
> >I think it's not a compound page problem.
> >We can face above problem where we allocates big order page without __GFP_COMP
> >and free middle page of it.
> >
> >Fortunately, We can catch such a problem by put_page_testzero in __free_pages
> >if you enable CONFIG_DEBUG_VM.
> >
> >Did you tried that with CONFIG_DEBUG_VM?
> >
>
> To be honest, I don't have a real test environment which brings this
> issue in the first place. On my simple test environment, enabling
> CONFIG_DEBUG_VM emits a bug when I tried to free middle of the slab
> pages. Thanks for pointing it out.
>
> However I guess there was a chance to bypass that test anyhow since
> it did reach to __free_pages_ok(). If the page count was 0 already,
> free_pages() will prevent it from getting to the function even
> though CONFIG_DEBUG_VM was disabled. But I don't think it's a kernel
> bug - it seems entirely our fault :( I'll recheck and talk about it
> with my colleagues.
Let me ask a question.
Could you see bad page message by PG_slab with SLUB after you apply your patch?
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next prev parent reply other threads:[~2012-03-05 10:59 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-29 8:54 [PATCH -next] slub: set PG_slab on all of slab pages Namhyung Kim
2012-02-29 15:24 ` Christoph Lameter
2012-03-01 7:30 ` Namhyung Kim
2012-03-01 15:03 ` Christoph Lameter
2012-03-02 7:12 ` Namhyung Kim
2012-03-02 16:13 ` Christoph Lameter
2012-03-04 10:34 ` Minchan Kim
2012-03-05 8:42 ` Namhyung Kim
2012-03-05 10:59 ` Minchan Kim [this message]
2012-03-05 14:48 ` Christoph Lameter
2012-03-06 1:16 ` Minchan Kim
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