linux-kernel - Re: [mmotm] BUG: Bad page state in process khugepaged ?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110211202431.GJ3347@random.random>
Date:	Fri, 11 Feb 2011 21:24:31 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>
Subject: Re: [mmotm] BUG: Bad page state in process khugepaged ?

On Fri, Feb 11, 2011 at 11:58:58AM -0800, Hugh Dickins wrote:
> Oh, I hadn't realized Fedora use it.  I wonder if that's wise, I thought
> Nick introduced it partly for the more expensive checks, and there might
> be one or two of those around - those bad_range()s in page_alloc.c?

I doubt the more expensive checks are very measurable.. benchmarks
usually run on enterprise distro. I'm sure when they enabled, they
were aware of having to run more expensive runtime checks.

> But the patch actually says -1024*1024: either would do.

I actually increased it to -1024*1024 after writing the email ;) sorry
the for the confusion.

> Yes, that's fine, 0xfff00000 looks unlikely enough (and my
> imagination for "deadbeef"-like magic is too drowsy today).

I used a negative power of two even if I doubt the compiler can make
much use of it.

> Okay I suppose: it seems rather laboured to me, I think I'd have just
> moved the VM_BUG_ON into rmv_page_order() if I'd done the patch; but
> since I was too lazy to do it, I'd better be grateful for yours!

Ok the reason I didn't move the VM_BUG_ON is to be stricter in case
there are more usages of __ClearPageBuddy in the future. I guess it's
not so important, but when I initially implemented it, it wasn't
entirely obvious it would work safe with memory hotplug, compaction
and all other bits using PageBuddy, so...
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/