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Mon, 25 May 2020 08:12:42 +0000 (UTC) Date: Mon, 25 May 2020 10:12:41 +0200 From: Sergio Lopez To: Stefan Hajnoczi Subject: Re: [PATCH 3/7] block/nvme: don't access CQE after moving cq.head Message-ID: <20200525081241.cbsgtyi6pf7dkyyf@dritchie> References: <20200519171138.201667-1-stefanha@redhat.com> <20200519171138.201667-4-stefanha@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200519171138.201667-4-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="6vuejpxec6v6tliy" Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=slp@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/25 01:54:11 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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 , qemu-block@nongnu.org, qemu-devel@nongnu.org, Max Reitz , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --6vuejpxec6v6tliy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, May 19, 2020 at 06:11:34PM +0100, Stefan Hajnoczi wrote: > Do not access a CQE after incrementing q->cq.head and releasing q->lock. > It is unlikely that this causes problems in practice but it's a latent > bug. >=20 > The reason why it should be safe at the moment is that completion > processing is not re-entrant and the CQ doorbell isn't written until the > end of nvme_process_completion(). >=20 > Make this change now because QEMU expects completion processing to be > re-entrant and later patches will do that. >=20 > Signed-off-by: Stefan Hajnoczi > --- > block/nvme.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) Reviewed-by: Sergio Lopez --6vuejpxec6v6tliy Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEvtX891EthoCRQuii9GknjS8MAjUFAl7LffgACgkQ9GknjS8M AjUayg/+N55PRalxTmZznvUaQcwekZgdNEGKY1nm8deogZfKNxVGl/GSfwAy9p/4 3luMvYcvUZp2eE7ANeXnhjGS3zm9SyKELZPhcTi220vH10ROdjjS9ZI/lqRBuW5h TS+xwYmwK0ylkeCfWTiCUsp/CsPCU4yRhvikN48z3IHQRtgnK5WfpneXxOoRODAx 1HfsTqqiaNbJJSu1j0lzzUco2tQL22J6OyTzvLwv3VjQ70xiIrJbHFNjmBPSBiCB aKxEtwVJQGmrKqHrkkG4TnOSe25SlOZaWP8SidTJk9lgGUBJnMhplX1q/11IJSbc l9WNubRZFXwHFmj2AUQ9Xa6bK8p52ofAFOEu5drHm0umPYgFMVBlS/L9vKw0Skvt uCBm5Jvqh30T6jUntETgjRTR5WaKmsbIJiikQDUOk0vonfA6RluqcyIWNUjXsMmR kxb6wPKnwHNwjzCz2LZCJ2hkfv7KkB1jz53eAMBrg2w3n2f0fHeE62FUU51Ss3Bj zP6l2Ten0xg10UoPGIPkV/5HwrcFvcr9EIVlHhu5qJcId0nBnvfONT4rUBLyfPaI Qn74766YCvHrVR8kcMBaYnMXPJ4aBy5YRQCrFXTZx4F4khhJzWB2Z2EmFQmPBBxl YVpnA+qdIQy4Va6lMuo+wG0XHWK6eSM18/sVSdApVlI/O4uUKUo= =JWPW -----END PGP SIGNATURE----- --6vuejpxec6v6tliy--