Re: [PATCH] x86: revert "x86: Fix S4 regression"

[Dave Young]

On 07/23/2012 07:22 PM, Takao Indoh wrote:

> (2012/07/23 19:00), Dave Young wrote:
>> On 07/17/2012 11:15 AM, Takao Indoh wrote:
>>
>>> Hi Cong,
>>>
>>> When I tested kdump with 3.5.0-rc6 kernel, I found a problem of kdump
>>> kernel's panic in find_early_table_space().
>>>
>>> init_memory_mapping: [mem 0x00000000-0x36ffafff]
>>> Kernel panic - not syncing: Cannot find space for the kernel page tables
>>> Pid: 0, comm: swapper Not tainted 3.5.0-rc6 #17
>>> Call Trace:
>>>   [<ffffffff8158549b>] panic+0xb8/0x1c8
>>>   [<ffffffff8158565d>] ? printk+0x48/0x4a
>>>   [<ffffffff8157304c>] init_memory_mapping+0x46c/0x530
>>>   [<ffffffff818a73c7>] setup_arch+0x669/0xb0e
>>>   [<ffffffff8158565d>] ? printk+0x48/0x4a
>>>   [<ffffffff818a3a1f>] start_kernel+0x9b/0x34a
>>>   [<ffffffff818a332d>] x86_64_start_reservations+0x131/0x136
>>>   [<ffffffff818a341f>] x86_64_start_kernel+0xed/0xf4
>>>
>>> In find_early_table_space(), a kernel tries to find free area below 512M
>>> for pgtable using memblock_find_in_range, but it fails because kdump
>>> kernel does not have enough free space below 512M due to the memmap
>>> restriction. This is the memmap option specified against kdump kernel
>>> when crashkernel=128M.
>>>
>>> memmap=560K@64K memmap=130492K@770608K
>>>
>>> Only 560KB area is available and it is not sufficient for pgtable (it
>>> seems that about 1.8MB area is needed for pgtable). This problem is
>>> fixed by your revert patch. I hope this patch gets merged.
>>
>>
>> I can reproduce this issue as well, probably related to some x86 mm init
>> commits, this alloc failure does not happen with reverting below commits:
>>
>> bd2753b2dda7bb43c7468826de75f49c6a7e8965
>> 722bc6b16771ed80871e1fd81c86d3627dda2ac8
> Yeah, my result of bisect is as follows and at first I thought the
> commit 722bc6 caused this regression.
> 
> 722bc6b16771ed80871e1fd81c86d3627dda2ac8 is the first bad commit
> commit 722bc6b16771ed80871e1fd81c86d3627dda2ac8
> Author: WANG Cong <xiyou.wangcong@xxxxxxxxx>
> Date:   Mon Mar 5 15:05:13 2012 -0800
> 
> IIUC, this commit just fixes a bug of counting pgtable entries. As the
> result, another problem came up to the surface. In the case of my
> machine(16GB memory), before applying 722bc6, find_early_table_space()
> requests about 12KB free area and it can be got from 560K@64K area
> luckily. I think the size find_early_table_space() requests was a bug.
> After the bug is fixed by the commit 722bc6, find_early_table_space()
> requires 1.8MB area and it fails as I wrote.


Sounds reasonable, if find_early_table_space is ok then I also vote to
revert the s4 regression fix.

> 
> Thanks,
> Takao Indoh
> 
>>
>>>
>>> Thanks,
>>> Takao Indoh
>>>
>>> (2012/06/12 14:21), Cong Wang wrote:
>>>> From: Cong Wang <xiyou.wangcong@xxxxxxxxx>
>>>>
>>>> This reverts the following commit:
>>>>
>>>> 	commit 8548c84da2f47e71bbbe300f55edb768492575f7
>>>> 	Author: Takashi Iwai <tiwai@xxxxxxx>
>>>> 	Date:   Sun Oct 23 23:19:12 2011 +0200
>>>>
>>>> 	    x86: Fix S4 regression
>>>> 	
>>>> 	    Commit 4b239f458 ("x86-64, mm: Put early page table high") causes a S4
>>>> 	    regression since 2.6.39, namely the machine reboots occasionally at S4
>>>> 	    resume.  It doesn't happen always, overall rate is about 1/20.  But,
>>>> 	    like other bugs, once when this happens, it continues to happen.
>>>> 	
>>>> 	    This patch fixes the problem by essentially reverting the memory
>>>> 	    assignment in the older way.
>>>>
>>>> According to the previous discussion:
>>>> http://marc.info/?l=linux-kernel&m=133161674120253&w=2
>>>> it seems that so far the best solution is just reverting it.
>>>>
>>>> Takashi, could you help to test if the S4 regression is still
>>>> there after this patch?
>>>>
>>>> Reported-by: CAI Qian <caiqian@xxxxxxxxxx>
>>>> Cc: Dave Young <dyoung@xxxxxxxxxx>
>>>> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
>>>> Cc: Rafael J. Wysocki <rjw@xxxxxxx>
>>>> Cc: Yinghai Lu <yinghai.lu@xxxxxxxxxx>
>>>> Cc: Takashi Iwai <tiwai@xxxxxxx>
>>>> Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
>>>>
>>>> ---
>>>>    arch/x86/mm/init.c |    3 ++-
>>>>    1 files changed, 2 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
>>>> index bc4e9d8..7ab7975 100644
>>>> --- a/arch/x86/mm/init.c
>>>> +++ b/arch/x86/mm/init.c
>>>> @@ -74,8 +74,9 @@ static void __init find_early_table_space(struct map_range *mr, unsigned long en
>>>>    #ifdef CONFIG_X86_32
>>>>    	/* for fixmap */
>>>>    	tables += roundup(__end_of_fixed_addresses * sizeof(pte_t), PAGE_SIZE);
>>>> -#endif
>>>> +
>>>>    	good_end = max_pfn_mapped << PAGE_SHIFT;
>>>> +#endif
>>>>    
>>>>    	base = memblock_find_in_range(start, good_end, tables, PAGE_SIZE);
>>>>    	if (!base)
>>>>
>>
>>
>>
> 



-- 
Thanks
Dave
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