linux-kernel - Re: [PATCH V4] mm: fix kernel crash in khugepaged thread

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Message-Id: <2F74FF6B-66DC-4BF9-972A-C2F5FFFA979F@gmail.com>
Date:	Mon, 16 Nov 2015 09:35:53 +0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>, Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ebru Akagunduz <ebru.akagunduz@...il.com>,
	Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	jmarchan@...hat.com, mgorman@...hsingularity.net,
	willy@...ux.intel.com, linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org
Subject: Re: [PATCH V4] mm: fix kernel crash in khugepaged thread


> On Nov 13, 2015, at 22:01, Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> On Fri, 13 Nov 2015 19:54:11 +0800
> yalin wang <yalin.wang2010@...il.com> wrote:
> 
>>>>> 	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.  
> 
> hmm, pfn is defined as an unsigned long, would -1 be the best.
> Or should it be (-1UL).
> 
> Then we could also have:
> 
>        TP_printk("mm=%p, scan_pfn=0x%lx%s, writable=%d, referenced=%d, none_or_zero=%d, status=%s, unmapped=%d",
>                __entry->mm,
>                __entry->pfn == (-1UL) ? 0 : __entry->pfn,
> 		__entry->pfn == (-1UL) ? "(null)" : "",
> 
> Note the added %s after %lx I have in the print format.
> 
> -- Steve
it is not easy to print for perf tools in userspace ,
if you use this format ,
for user space perf tool, it print the entry by look up the member in entry struct by offset ,
you print a dynamic string which user space perf tool don’t know how to print this string .

Thanks --
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