Re: [PATCH] mm: Generalize and rename notify_page_fault() as kprobe_page_fault()

From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Mark Rutland <mark.rutland@arm.com>,
	Michal Hocko <mhocko@suse.com>,
	linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Will Deacon <will.deacon@arm.com>,
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	sparclinux@vger.kernel.org,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	linux-s390@vger.kernel.org,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Michael Ellerman <mpe@ellerman.id.au>,
	x86@kernel.org, Russell King <linux@armlinux.org.uk>,
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	Ingo Molnar <mingo@redhat.com>, James Hogan <jhogan@kernel.org>,
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	Tony Luck <tony.luck@intel.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Vineet Gupta <vgupta@synopsys.com>,
	linux-mips@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
	Paul Burton <paul.burton@mips.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linuxppc-dev@lists.ozlabs.org,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH] mm: Generalize and rename notify_page_fault() as kprobe_page_fault()
Date: Sun, 30 Jun 2019 10:11:03 +0530	[thread overview]
Message-ID: <78863cd0-8cb5-c4fd-ed06-b1136bdbb6ef@arm.com> (raw)
In-Reply-To: <20190629145009.GA28613@roeck-us.net>

Hello Guenter,

On 06/29/2019 08:20 PM, Guenter Roeck wrote:
> Hi,
> 
> On Thu, Jun 13, 2019 at 03:37:24PM +0530, Anshuman Khandual wrote:
>> Architectures which support kprobes have very similar boilerplate around
>> calling kprobe_fault_handler(). Use a helper function in kprobes.h to unify
>> them, based on the x86 code.
>>
>> This changes the behaviour for other architectures when preemption is
>> enabled. Previously, they would have disabled preemption while calling the
>> kprobe handler. However, preemption would be disabled if this fault was
>> due to a kprobe, so we know the fault was not due to a kprobe handler and
>> can simply return failure.
>>
>> This behaviour was introduced in the commit a980c0ef9f6d ("x86/kprobes:
>> Refactor kprobes_fault() like kprobe_exceptions_notify()")
>>
> 
> With this patch applied, parisc:allmodconfig images no longer build.
> 
> In file included from arch/parisc/mm/fixmap.c:8:
> include/linux/kprobes.h: In function 'kprobe_page_fault':
> include/linux/kprobes.h:477:9: error:
> 	implicit declaration of function 'kprobe_fault_handler'; did you mean 'kprobe_page_fault'?

Yikes.. Arch parisc does not even define (unlike mips which did but never exported)
now required function kprobe_fault_handler() when CONFIG_KPROBES is enabled.

I believe rather than defining one stub version only for parsic it would be better
to have an weak symbol generic stub definition for kprobe_fault_handler() in file
include/linux/kprobes.h when CONFIG_KPROBES is enabled along side the other stub
definition when !CONFIG_KPROBES. But arch which wants to use kprobe_page_fault()
cannot use stub kprobe_fault_handler() definition and will have to provide one.
I will probably add a comment regarding this.

> 
> Reverting the patch fixes the problem.
> 
> Guenter
> 

Thanks for reporting the problem.