On Thu, 12 Nov 2015 16:21:02 +0800
yalin wang <yalin.wang2010@xxxxxxxxx> 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?
> avoid trace NULL page.
>
> Signed-off-by: yalin wang <yalin.wang2010@xxxxxxxxx>
> ---
> 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;
But if there's no reason to do the tracepoint if page is NULL, then
this patch is fine. I'm just throwing out this idea.
-- Steve
> __entry->writable = writable;
> __entry->referenced = referenced;
> __entry->none_or_zero = none_or_zero;
> @@ -106,12 +108,14 @@ TRACE_EVENT(mm_collapse_huge_page,
> __print_symbolic(__entry->status, SCAN_STATUS))
> );
>
> -TRACE_EVENT(mm_collapse_huge_page_isolate,
> +TRACE_EVENT_CONDITION(mm_collapse_huge_page_isolate,
>
> - TP_PROTO(unsigned long pfn, int none_or_zero,
> + TP_PROTO(struct page *page, int none_or_zero,
> bool referenced, bool writable, int status),
>
> - TP_ARGS(pfn, none_or_zero, referenced, writable, status),
> + TP_ARGS(page, none_or_zero, referenced, writable, status),
> +
> + TP_CONDITION(page),
>
> TP_STRUCT__entry(
> __field(unsigned long, pfn)
\
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