linux-kernel - Re: [-rc7 regression] Buggy commit: "mm: use aligned zone start for pfn_to

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Date:	Sat, 16 Feb 2013 09:29:54 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Greg KH <greg@...ah.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Greg KH <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Alexander Viro <viro@....linux.org.uk>,
	Theodore Ts'o <tytso@....edu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [-rc7 regression] Buggy commit: "mm: use aligned zone start for
 pfn_to_bitidx calculation"


* Greg KH <greg@...ah.com> wrote:

> On Fri, Feb 15, 2013 at 12:44:26PM +0100, Ingo Molnar wrote:
> > 
> > [ Greg: -stable was Cc:-ed for this potentially buggy commit. ]
> > 
> > * Yinghai Lu <yinghai@...nel.org> wrote:
> > 
> > > On Thu, Feb 14, 2013 at 7:08 AM, Ingo Molnar <mingo@...nel.org> wrote:
> > > > these three:
> > > >
> > > > 10d73e655cef mm: bootmem: fix free_all_bootmem_core() with odd bitmap alignment
> > > > c060f943d092 mm: use aligned zone start for pfn_to_bitidx calculation
> > > > c0232ae861df mm: memblock: fix wrong memmove size in memblock_merge_regions()
> > > >
> > > > might have highmem=512m boot parameter sensitivity.
> > > 
> > > 10d73e655cef should not be related, as we are using nobootmem wrapper
> > > of memblock.
> > > c0232ae861df is copying less while using the blank slot in memblock
> > > memory or reserved array
> > > so it should be ok too.
> > > 
> > > c060f943d092 may be related as you config does not have
> > > CONFIG_SPARSEMEM defined.
> > 
> > Right, that's the commit causing the x86 regression:
> > 
> >  c060f943d0929f3e429c5d9522290584f6281d6e is the first bad commit
> >  commit c060f943d0929f3e429c5d9522290584f6281d6e
> >  Date:   Fri Jan 11 14:31:51 2013 -0800
> > 
> >      mm: use aligned zone start for pfn_to_bitidx calculation
> > 
> > I've given 6d92d4f (its parent commit) quite a bit of testing so 
> > I'm 99% sure in the validity of this bisection result.
> > 
> > Involved parties Cc:-ed.
> > 
> > Revert attached below - it reverts cleanly and I'll test this 
> > today, to see whether this solves the sporadic lockups.
> > 
> > Thanks,
> > 
> > 	Ingo
> > 
> > ------------------->
> > >From 6f3d5a8f38eb23f792b408d9bc8fee53a7d158f9 Mon Sep 17 00:00:00 2001
> > From: Ingo Molnar <mingo@...nel.org>
> > Date: Fri, 15 Feb 2013 12:43:22 +0100
> > Subject: [PATCH] Revert "mm: use aligned zone start for pfn_to_bitidx
> >  calculation"
> > 
> > This reverts commit c060f943d0929f3e429c5d9522290584f6281d6e.
> 
> Let me know if I should be reverting this from the -stable releases.

It appears so - it definitely locks up here with the config I 
sent. It appears to be a rare bug but a bug.

Would be nice to hear from the authors/ackers/pushers of the 
patch though.

Thanks,

	Ingo
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