Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752189AbdI2KYj (ORCPT ); Fri, 29 Sep 2017 06:24:39 -0400 Received: from mail-pg0-f68.google.com ([74.125.83.68]:36839 "EHLO mail-pg0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751970AbdI2KYh (ORCPT ); Fri, 29 Sep 2017 06:24:37 -0400 X-Google-Smtp-Source: AOwi7QDHDXAjlnUQeNaGs6DxO5eVw9h2zQ/jNVVUbRHkPU3nzZXcyABS57v00kALkhxKhEHuOKh0Dw== Date: Fri, 29 Sep 2017 18:25:04 +0800 From: Boqun Feng To: Paolo Bonzini Cc: "Paul E. McKenney" , "Levin, Alexander (Sasha Levin)" , Sasha Levin , "linux-kernel@vger.kernel.org List" , Ingo Molnar , "jiangshanlai@gmail.com" , "dipankar@in.ibm.com" , Andrew Morton , Mathieu Desnoyers , Josh Triplett , Thomas Gleixner , Peter Zijlstra , "dhowells@redhat.com" , Eric Dumazet , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Oleg Nesterov , "bobby.prani@gmail.com" , Radim =?utf-8?B?S3LEjW3DocWZ?= , kvm@vger.kernel.org Subject: Re: [PATCH v3 tip/core/rcu 40/40] rcu: Make non-preemptive schedule be Tasks RCU quiescent state Message-ID: <20170929102504.52ivxyr4va6xe3e5@tardis> References: <20170419165805.GB10874@linux.vnet.ibm.com> <1492621117-13939-40-git-send-email-paulmck@linux.vnet.ibm.com> <20170928123055.GI3521@linux.vnet.ibm.com> <20170928153813.7cernglt2d7umhpe@sasha-lappy> <20170928160514.GM3521@linux.vnet.ibm.com> <20170929093010.w56nawdoz23mkzio@tardis> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="44k73p7comzjrmlc" Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170912 (1.9.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3345 Lines: 101 --44k73p7comzjrmlc Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Sep 29, 2017 at 10:01:24AM +0000, Paolo Bonzini wrote: > On 29/09/2017 11:30, Boqun Feng wrote: > > On Thu, Sep 28, 2017 at 04:05:14PM +0000, Paul E. McKenney wrote: > > [...] > >>> __schedule+0x201/0x2240 kernel/sched/core.c:3292 > >>> schedule+0x113/0x460 kernel/sched/core.c:3421 > >>> kvm_async_pf_task_wait+0x43f/0x940 arch/x86/kernel/kvm.c:158 > >> > >> It is kvm_async_pf_task_wait() that calls schedule(), but it carefully > >> sets state to make that legal. Except... > >> > >>> do_async_page_fault+0x72/0x90 arch/x86/kernel/kvm.c:271 > >>> async_page_fault+0x22/0x30 arch/x86/entry/entry_64.S:1069 > >>> RIP: 0010:format_decode+0x240/0x830 lib/vsprintf.c:1996 > >>> RSP: 0018:ffff88003b2df520 EFLAGS: 00010283 > >>> RAX: 000000000000003f RBX: ffffffffb5d1e141 RCX: ffff88003b2df670 > >>> RDX: 0000000000000001 RSI: dffffc0000000000 RDI: ffffffffb5d1e140 > >>> RBP: ffff88003b2df560 R08: dffffc0000000000 R09: 0000000000000000 > >>> R10: ffff88003b2df718 R11: 0000000000000000 R12: ffff88003b2df5d8 > >>> R13: 0000000000000064 R14: ffffffffb5d1e140 R15: 0000000000000000 > >>> vsnprintf+0x173/0x1700 lib/vsprintf.c:2136 > >> > >> We took a page fault in vsnprintf() while doing link_path_walk(), > >> which looks to be within an RCU read-side critical section. > >> > >> Maybe the page fault confused lockdep? > >> > >> Sigh. It is going to be a real pain if all printk()s need to be > >> outside of RCU read-side critical sections due to the possibility of > >> page faults... > >> > >=20 > > Does this mean whenever we get a page fault in a RCU read-side critical > > section, we may hit this? > >=20 > > Could we simply avoid to schedule() in kvm_async_pf_task_wait() if the > > fault process is in a RCU read-side critical section as follow? > >=20 > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > > index aa60a08b65b1..291ea13b23d2 100644 > > --- a/arch/x86/kernel/kvm.c > > +++ b/arch/x86/kernel/kvm.c > > @@ -140,7 +140,7 @@ void kvm_async_pf_task_wait(u32 token) > > =20 > > n.token =3D token; > > n.cpu =3D smp_processor_id(); > > - n.halted =3D is_idle_task(current) || preempt_count() > 1; > > + n.halted =3D is_idle_task(current) || preempt_count() > 1 || rcu_pree= mpt_depth(); > > init_swait_queue_head(&n.wq); > > hlist_add_head(&n.link, &b->list); > > raw_spin_unlock(&b->lock); > >=20 > > (Add KVM folks and list Cced) >=20 > Yes, that would work. Mind to send it as a proper patch? >=20 I'd love to ;-) In a minute. Regards, Boqun > Thanks, >=20 > Paolo >=20 > > Regards, > > Boqun > >=20 > >> Thanx, Paul > > [...] > >=20 >=20 >=20 --44k73p7comzjrmlc Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEj5IosQTPz8XU1wRHSXnow7UH+rgFAlnOH3QACgkQSXnow7UH +rhNrQf/XFoaAymNhP6b9F3duFIq0wE+7fAx+/Mo4TLnil36Eq3L4oMZxMARNko2 giqF38qhPaGCm9KDfPJRGk/FvZZt70vlRlyBen7HkHbaSdNRSYox5XOcZp+8Qap8 5at2nMDtK+7WAsom3+N32yrpxSe+eHGup7Jke/+JCm6HPThQ5yVQ692kV7ZRXNYA ryq2JMajSHTSPqwusZKG984JSCWSlhbaPzhFsDMKfSncFou8fYKUTO560qNBFe3B ZWBKXjwNBJHUlqDNTwB2ZgRljMKal8cJSWmdgjYJTQlfpJ2GW8QNZ0gtnJFeC3pX C+cUmQ5mbkxCmMoZsBug5ZMQc7jCIA== =R1EX -----END PGP SIGNATURE----- --44k73p7comzjrmlc--