[PATCH] arm64: mm: Fix false positives in set_pte_at access/dirty race detection

[Yisheng Xie]

Hi Will,

On 2017/12/13 17:21, Will Deacon wrote:
> Hi Yisheng,
> 
> On Wed, Dec 13, 2017 at 09:01:23AM +0800, Yisheng Xie wrote:
>> On 2017/12/12 19:43, Will Deacon wrote:
>>> Jiankang reports that our race detection in set_pte_at is firing when
>>> copying the page tables in dup_mmap as a result of a fork(). In this
>>> situation, the page table isn't actually live and so there is no way
>>> that we can race with a concurrent update from the hardware page table
>>> walker.
>>>
>>> This patch reworks the race detection so that we require either the
>>> mm to match the current active_mm (i.e. currently installed in our TTBR0)
>>> or the mm_users count to be greater than 1, implying that the page table
>>> could be live in another CPU. The mm_users check might still be racy,
>>> but we'll avoid false positives and it's not realistic to validate that
>>> all the necessary locks are held as part of this assertion.
>>>
>>> Cc: Yisheng Xie <xieyisheng1 at huawei.com>
>>> Reported-by: Jiankang Chen <chenjiankang1 at huawei.com>
>>> Tested-by: Jiankang Chen <chenjiankang1 at huawei.com>
>>> Signed-off-by: Will Deacon <will.deacon at arm.com>
>>> ---
>>>  arch/arm64/include/asm/pgtable.h | 8 ++++----
>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
>>> index 3ff03a755c32..bdcc7f1c9d06 100644
>>> --- a/arch/arm64/include/asm/pgtable.h
>>> +++ b/arch/arm64/include/asm/pgtable.h
>>> @@ -42,6 +42,8 @@
>>>  #include <asm/cmpxchg.h>
>>>  #include <asm/fixmap.h>
>>>  #include <linux/mmdebug.h>
>>> +#include <linux/mm_types.h>
>>> +#include <linux/sched.h>
>>>  
>>
>> Do you have compiled kernel after apply this patch? In our environment, it will
>> fail to compile kernel if include file here(I will attach some log later).
>> Instead, we move these included file after mmdebug.h, and I do not know whether
>> this is just my compiler's problem:
> 
> It compiles fine for me. Are you seeing a problem building this on top of
> mainline? If so, what is your .config?

Oh, you have already moved it after #ifndef __ASSEMBLY__ , sorry for not finding
this when review this patch.

And I also have just compiled with this patch in mainline, is ok.
Thanks for your help.

Thanks
Yisheng Xie

> 
>>   --- a/arch/arm64/include/asm/pgtable.h
>>   +++ b/arch/arm64/include/asm/pgtable.h
>>   @@ -42,6 +42,8 @@
>>    #include <asm/cmpxchg.h>
>>    #include <asm/fixmap.h>
>>    #include <linux/mmdebug.h>
>>    +#include <linux/mm_types.h>
>>    +#include <linux/sched.h>
>>
>> Sorry for not having told you this information.
>>
>> Thanks
>> Yisheng Xie
>>
>> compiler err log: ==========
>> [...]
>> include/linux/mm_types_task.h:60: Error: unknown mnemonic `struct' -- `struct page_frag{'
>> include/asm-generic/preempt.h:9: Error: unknown mnemonic `static' -- `static inline int preempt_count(void)'
>> include/linux/mm_types_task.h:61: Error: unknown mnemonic `struct' -- `struct page*page'
>> include/asm-generic/preempt.h:10: Error: junk at end of line, first unrecognized character is `{'
>> include/linux/mm_types_task.h:63: Error: unknown mnemonic `__u32' -- `__u32 offset'
>> include/asm-generic/preempt.h:11: Error: unknown mnemonic `return' -- `return READ_ONCE(((struct thread_info*)current)->preempt_count)'
>> include/linux/mm_types_task.h:64: Error: unknown mnemonic `__u32' -- `__u32 size'
>> [...]
> 
> This looks like the includes are being pulled into an assembly file, but
> this part is guarded by #ifndef __ASSEMBLY__ so I can't see how that could
> happen.
> 
> Will
> 
> .
>