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received-spf: None (protection.outlook.com: microsoft.com does not designate permitted sender hosts) authentication-results: spf=none (sender IP is ) smtp.mailfrom=Alexander.Levin@microsoft.com; x-microsoft-antispam-message-info: Np8RPECR65b07QExGMziUmOZ6v7esRiXxHX7VKWwO/f0CXz7tHIQyIWsyro3vjZXTejep7WxxmVap+dI9aVr/ax/qLSj6nyFXNoxKvrICE6LU55U64XGlGZTFY9ko1oQ/z1qoTGNI8T91nt42ajDGvq/sKi9/fiopj1d0c3glIaor3DqRPkwtjmXW61/Lv52/RjnUInCMfD2yTUt5Ejjwgbl8k/fsWvMWqcHdzGN0diqNMcUM7RkRedMaL5wASR5w19YyXs5Ra+qsWSR4KMh9VAVHfnbKSAPKjbQGXOokthH+WNO+Y+qXb3auJGyahUDR7+NwnN91BD3MfYNvhFdEqPQrC74MougtItSQjFHyFk= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: eb6f5635-58c6-43a4-3348-08d62736775e X-MS-Exchange-CrossTenant-originalarrivaltime: 01 Oct 2018 00:39:14.6851 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR21MB0120 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vitaly Kuznetsov [ Upstream commit 87dffe86d406bee8782cac2db035acb9a28620a7 ] When guest receives a sysrq request from the host it acknowledges it by writing '\0' to control/sysrq xenstore node. This, however, make xenstore watch fire again but xenbus_scanf() fails to parse empty value with "%c" format string: sysrq: SysRq : Emergency Sync Emergency Sync complete xen:manage: Error -34 reading sysrq code in control/sysrq Ignore -ERANGE the same way we already ignore -ENOENT, empty value in control/sysrq is totally legal. Signed-off-by: Vitaly Kuznetsov Reviewed-by: Wei Liu Signed-off-by: Boris Ostrovsky Signed-off-by: Sasha Levin --- drivers/xen/manage.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c index 587d12829925..0444ebdda3f0 100644 --- a/drivers/xen/manage.c +++ b/drivers/xen/manage.c @@ -283,9 +283,11 @@ static void sysrq_handler(struct xenbus_watch *watch, = const char *path, /* * The Xenstore watch fires directly after registering it and * after a suspend/resume cycle. So ENOENT is no error but - * might happen in those cases. + * might happen in those cases. ERANGE is observed when we get + * an empty value (''), this happens when we acknowledge the + * request by writing '\0' below. */ - if (err !=3D -ENOENT) + if (err !=3D -ENOENT && err !=3D -ERANGE) pr_err("Error %d reading sysrq code in control/sysrq\n", err); xenbus_transaction_end(xbt, 1); --=20 2.17.1