From mboxrd@z Thu Jan  1 00:00:00 1970
From: Matthew Wilcox <willy@infradead.org>
Date: Fri, 31 May 2019 17:48:54 +0000
Subject: Re: [RFC] mm: Generalize notify_page_fault()
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To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>, Michal Hocko <mhocko@suse.com>, linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, linux-mm@kvack.org, Paul Mackerras <paulus@samba.org>, sparclinux@vger.kernel.org, linux-s390@vger.kernel.org, Yoshinori Sato <ysato@users.sourceforge.jp>, Michael Ellerman <mpe@ellerman.id.au>, Russell King <linux@armlinux.org.uk>, Fenghua Yu <fenghua.yu@intel.com>, Stephen Rothwell <sfr@canb.auug.org.au>, Andrey Konovalov <andreyknvl@google.com>, linux-arm-kernel@lists.infradead.org, Christophe Leroy <christophe.leroy@c-s.fr>, Tony Luck <tony.luck@intel.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, linux-kernel@vger.kernel.org, Martin Schwidefsky <schwidefsky@de.ibm.com>, Andrew Morton <akpm@linux-foundation.org>, linuxppc-dev@lists.ozlabs.org, "David S. Miller" <davem@davemloft.net>

On Fri, May 31, 2019 at 02:17:43PM +0530, Anshuman Khandual wrote:
> On 05/30/2019 07:09 PM, Matthew Wilcox wrote:
> > On Thu, May 30, 2019 at 05:31:15PM +0530, Anshuman Khandual wrote:
> >> On 05/30/2019 04:36 PM, Matthew Wilcox wrote:
> >>> The two handle preemption differently.  Why is x86 wrong and this one
> >>> correct?
> >>
> >> Here it expects context to be already non-preemptible where as the proposed
> >> generic function makes it non-preemptible with a preempt_[disable|enable]()
> >> pair for the required code section, irrespective of it's present state. Is
> >> not this better ?
> > 
> > git log -p arch/x86/mm/fault.c
> > 
> > search for 'kprobes'.
> > 
> > tell me what you think.
> 
> Are you referring to these following commits
> 
> a980c0ef9f6d ("x86/kprobes: Refactor kprobes_fault() like kprobe_exceptions_notify()")
> b506a9d08bae ("x86: code clarification patch to Kprobes arch code")
> 
> In particular the later one (b506a9d08bae). It explains how the invoking context
> in itself should be non-preemptible for the kprobes processing context irrespective
> of whether kprobe_running() or perhaps smp_processor_id() is safe or not. Hence it
> does not make much sense to continue when original invoking context is preemptible.
> Instead just bail out earlier. This seems to be making more sense than preempt
> disable-enable pair. If there are no concerns about this change from other platforms,
> I will change the preemption behavior in proposed generic function next time around.

Exactly.

So, any of the arch maintainers know of a reason they behave differently
from x86 in this regard?  Or can Anshuman use the x86 implementation
for all the architectures supporting kprobes?