> On Nov 13, 2015, at 18:47, Vlastimil Babka <vba...@suse.cz> wrote:
>
> On 11/12/2015 03:29 PM, Steven Rostedt wrote:
>> On Thu, 12 Nov 2015 16:21:02 +0800
>> yalin wang <yalin.wang2...@gmail.com> wrote:
>>
>>> This crash is caused by NULL pointer deference, in page_to_pfn() marco,
>>> when page == NULL :
>>>
>>> [ 182.639154 ] Unable to handle kernel NULL pointer dereference at virtual
>>> address 00000000
>>
>>
>>> add the trace point with TP_CONDITION(page),
>>
>> I wonder if we still want to trace even if page is NULL?
>
> I'd say we want to. There's even a "SCAN_PAGE_NULL" result defined for that
> case, and otherwise we would only have to guess why collapsing failed, which
> is the thing that the tracepoint should help us find out in the first place :)
>
>>> avoid trace NULL page.
>>>
>>> Signed-off-by: yalin wang <yalin.wang2...@gmail.com>
>>> ---
>>> include/trace/events/huge_memory.h | 20 ++++++++++++--------
>>> mm/huge_memory.c | 6 +++---
>>> 2 files changed, 15 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/include/trace/events/huge_memory.h
>>> b/include/trace/events/huge_memory.h
>>> index 11c59ca..727647b 100644
>>> --- a/include/trace/events/huge_memory.h
>>> +++ b/include/trace/events/huge_memory.h
>>> @@ -45,12 +45,14 @@ SCAN_STATUS
>>> #define EM(a, b) {a, b},
>>> #define EMe(a, b) {a, b}
>>>
>>> -TRACE_EVENT(mm_khugepaged_scan_pmd,
>>> +TRACE_EVENT_CONDITION(mm_khugepaged_scan_pmd,
>>>
>>> - TP_PROTO(struct mm_struct *mm, unsigned long pfn, bool writable,
>>> + TP_PROTO(struct mm_struct *mm, struct page *page, bool writable,
>>> bool referenced, int none_or_zero, int status, int unmapped),
>>>
>>> - TP_ARGS(mm, pfn, writable, referenced, none_or_zero, status, unmapped),
>>> + TP_ARGS(mm, page, writable, referenced, none_or_zero, status, unmapped),
>>> +
>>> + TP_CONDITION(page),
>>>
>>> TP_STRUCT__entry(
>>> __field(struct mm_struct *, mm)
>>> @@ -64,7 +66,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
>>>
>>> TP_fast_assign(
>>> __entry->mm = mm;
>>> - __entry->pfn = pfn;
>>> + __entry->pfn = page_to_pfn(page);
>>
>> Instead of the condition, we could have:
>>
>> __entry->pfn = page ? page_to_pfn(page) : -1;
>
> I agree. Please do it like this.
ok , i will send V5 patch .--
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