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Thu, 7 Oct 2021 14:18:38 +0000 (UTC) Received: from localhost (unknown [10.39.194.238]) by smtp.corp.redhat.com (Postfix) with ESMTP id B5CA05C1CF; Thu, 7 Oct 2021 14:18:37 +0000 (UTC) Date: Thu, 7 Oct 2021 15:18:36 +0100 From: Stefan Hajnoczi To: Emanuele Giuseppe Esposito Subject: Re: [RFC PATCH v2 08/25] block: introduce assert_bdrv_graph_writable Message-ID: References: <20211005143215.29500-1-eesposit@redhat.com> <20211005143215.29500-9-eesposit@redhat.com> <9a778b91-d175-8062-6783-740ba42c4321@redhat.com> <4dfda254-2ff0-8977-9e42-8c0f5f1075d8@redhat.com> MIME-Version: 1.0 In-Reply-To: <4dfda254-2ff0-8977-9e42-8c0f5f1075d8@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="c/eSPTFfsdmqKDoK" Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -9 X-Spam_score: -1.0 X-Spam_bar: - X-Spam_report: (-1.0 / 5.0 requ) DKIMWL_WL_HIGH=-0.05, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Fam Zheng , Vladimir Sementsov-Ogievskiy , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Eduardo Habkost , qemu-block@nongnu.org, Juan Quintela , Eric Blake , Richard Henderson , qemu-devel@nongnu.org, Markus Armbruster , Hanna Reitz , Paolo Bonzini , John Snow , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --c/eSPTFfsdmqKDoK Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Oct 07, 2021 at 03:47:42PM +0200, Emanuele Giuseppe Esposito wrote: >=20 >=20 > On 07/10/2021 14:02, Paolo Bonzini wrote: > > > --- a/block/io.c > > > +++ b/block/io.c > > > @@ -739,6 +739,11 @@ void bdrv_drain_all(void) > > > =A0=A0=A0=A0=A0 bdrv_drain_all_end(); > > > =A0 } > > > +void assert_bdrv_graph_writable(BlockDriverState *bs) > > > +{ > > > +=A0=A0=A0 g_assert(qatomic_read(&bs->quiesce_counter) > 0 || > > > qemu_in_main_thread()); > > > +} > >=20 > > Hmm, wait - I think this should be an "&&", not an OR? > >=20 >=20 > You are right, && makes more sense. But as you said, using an AND will ma= ke > the assertion fail in multiple places, because the necessary drains are > missing. So I am going to remove the check for drains and leave it as tod= o. > I will handle this case in another patch. BTW when an assertion expression tests unrelated things it helps to use separate assert() calls instead of &&. That way it's obvious which sub-expression failed from the error message and it's not necessary to inspect the coredump. In other words: assert(a && b) -> Assertion `a && b` failed. This doesn't tell me whether it was a or b that was false. The assertion failure is easier to diagnose if you split it: assert(a); -> Assertion `a` failed. assert(b); -> Assertion `b` failed. 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