linux-kernel - Re: bisected boot regression post 2.6.25-rc3.. please revert

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Date:	Mon, 03 Mar 2008 10:36:10 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	torvalds@...ux-foundation.org, hans.rosenfeld@....com,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: bisected boot regression post 2.6.25-rc3.. please revert

Ingo Molnar wrote:
> * Arjan van de Ven <arjan@...ux.intel.com> wrote:
> 
>> ------------[ cut here ]------------
>> WARNING: at arch/x86/mm/pgtable_32.c:387 pmd_bad+0x44/0x53()
>> Modules linked in:
>> Pid: 1, comm: swapper Not tainted 2.6.25-rc3 #14
>>  [<c0424ba5>] warn_on_slowpath+0x41/0x67
>>  [<c0408c5c>] ? native_sched_clock+0x94/0xa6
>>  [<c043f432>] ? lock_release_holdtime+0x1a/0x115
>>  [<c04702d4>] ? handle_mm_fault+0x297/0x7e2
>>  [<c063eee6>] ? _spin_unlock+0x1d/0x20
>>  [<c04707f0>] ? handle_mm_fault+0x7b3/0x7e2
>>  [<c04851c1>] ? do_sync_read+0xab/0xe9
>>  [<c0417223>] pmd_bad+0x44/0x53
>>  [<c046f37f>] follow_page+0x8b/0x1f2
>>  [<c0470aa0>] get_user_pages+0x281/0x2ef
> 
> hm. I suspect some gcc related difference related to the handling of 
> this masking:
> 
>    pmd_val(x) & ~(PAGE_MASK | _PAGE_USER | _PAGE_PSE | _PAGE_NX)
> 
> versus:
> 
>    pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)
> 
> perhaps it will work if you change it to:
> 
>    pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER & ~_PAGE_PSE & ~_PAGE_NX)
> 
> ?
> 
> in any case, the commit has to be reverted as it clearly isnt a NOP on 
> your box as it was intended to be. (it should only have made a 
> difference in a rare hugetlbfs case)

interesting observation: if I turn the macros into inlines... the difference goes away.

I'm half tempted to just do it as inline period ... any objections ?
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