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:

quoted

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.

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