Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Date:   Mon, 30 May 2022 19:03:31 +0200
From:   Heiko Carstens <hca@linux.ibm.com>
To:     Peter Xu <peterx@redhat.com>
Cc:     Christian Borntraeger <borntraeger@linux.ibm.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Will Deacon <will@kernel.org>,
        Matt Turner <mattst88@gmail.com>, linux-s390@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Brian Cain <bcain@quicinc.com>, Borislav Petkov <bp@alien8.de>,
        linux-alpha@vger.kernel.org, Alistair Popple <apopple@nvidia.com>,
        Jonas Bonn <jonas@southpole.se>,
        linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
        Michael Ellerman <mpe@ellerman.id.au>,
        Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
        linux-snps-arc@lists.infradead.org,
        Vineet Gupta <vgupta@kernel.org>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
        Rich Felker <dalias@libc.org>, sparclinux@vger.kernel.org,
        Russell King <linux@armlinux.org.uk>,
        David Hildenbrand <david@redhat.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        "James E . J . Bottomley" <James.Bottomley@hansenpartnership.com>,
        linux-xtensa@linux-xtensa.org, linux-sh@vger.kernel.org,
        Paul Walmsley <paul.walmsley@sifive.com>,
        linux-m68k@lists.linux-m68k.org, linuxppc-dev@lists.ozlabs.org,
        Richard Henderson <rth@twiddle.net>,
        Guo Ren <guoren@kernel.org>, linux-parisc@vger.kernel.org,
        Andrea Arcangeli <aarcange@redhat.com>,
        Helge Deller <deller@gmx.de>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linux-um@lists.infradead.org, "H . Peter Anvin" <hpa@zytor.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        openrisc@lists.librecores.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-hexagon@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
        Stafford Horne <shorne@gmail.com>, linux-csky@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-mips@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Dinh Nguyen <dinguyen@kernel.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        "David S . Miller" <davem@davemloft.net>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Hugh Dickins <hughd@google.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-riscv@lists.infradead.org, Max Filippov <jcmvbkbc@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Johannes Berg <johannes@sipsolutions.net>,
        Chris Zankel <chris@zankel.net>,
        Michal Simek <monstr@monstr.eu>, x86@kernel.org,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Richard Weinberger <richard@nod.at>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared
 memory types
Message-ID: <YpT443jVZtM6p9OD@osiris>
References: <20220527193936.30678-1-peterx@redhat.com>
 <YpPYkzbrQmy4FjrI@osiris>
 <33fd4731-9765-d78b-bdc3-f8243c98e81f@linux.ibm.com>
 <YpToVpjXmdFqGOpY@xz-m1.local>
 <YpTqNKMTt8PoA41n@xz-m1.local>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YpTqNKMTt8PoA41n@xz-m1.local>
Precedence: bulk

On Mon, May 30, 2022 at 12:00:52PM -0400, Peter Xu wrote:
> On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote:
> > On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote:
> > > > diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> > > > index 4608cc962ecf..e1d40ca341b7 100644
> > > > --- a/arch/s390/mm/fault.c
> > > > +++ b/arch/s390/mm/fault.c
> > > > @@ -436,12 +436,11 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
> > > >   	/* The fault is fully completed (including releasing mmap lock) */
> > > >   	if (fault & VM_FAULT_COMPLETED) {
> > > > -		/*
> > > > -		 * Gmap will need the mmap lock again, so retake it.  TODO:
> > > > -		 * only conditionally take the lock when CONFIG_PGSTE set.
> > > > -		 */
> > > > -		mmap_read_lock(mm);
> > > > -		goto out_gmap;
> > > > +		if (gmap) {
> > > > +			mmap_read_lock(mm);
> > > > +			goto out_gmap;
> > > > +		}
			fault = 0;  <----
> > > > +		goto out;
> 
> Hmm, right after I replied I found "goto out" could be problematic, since
> all s390 callers of do_exception() will assume it an error condition (side
> note: "goto out_gmap" contains one step to clear "fault" to 0).  I'll
> replace this with "return 0" instead if it looks good to both of you.
> 
> I'll wait for a confirmation before reposting.  Thanks,

Right, that was stupid. Thanks for double checking!

However could you please add "fault = 0" just in front of the goto out
like above? I'd like to avoid having returns and gotos mixed.