Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Kar Hin Ong <kar.hin.ong@ni.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Keng Soon Cheah <keng.soon.cheah@ni.com>
Subject: Firing an interrupt pin induces the occurrence of another interrupt
Thread-Topic: Firing an interrupt pin induces the occurrence of another
 interrupt
Thread-Index: AdU9G2vsQGAkqV8+TnmePN80wZpMhw==
Date:   Thu, 18 Jul 2019 03:48:42 +0000
Message-ID: <DM6PR04MB6249DDAA6BCD01D1B37D41E8C3C80@DM6PR04MB6249.namprd04.prod.outlook.com>
Accept-Language: en-US
Content-Language: en-US
received-spf: None (protection.outlook.com: ni.com does not designate
 permitted sender hosts)
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: 2e936329-26d9-45e0-047b-08d70b32d3be
X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Jul 2019 03:48:42.3511
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 87ba1f9a-44cd-43a6-b008-6fdb45a5204e
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: kar.hin.ong@ni.com
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR04MB5868
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:5.22.84,1.0.8
 definitions=2019-07-18_01:2019-07-17,2019-07-18 signatures=0
X-Proofpoint-Spam-Details: rule=inbound_policy_notspam policy=inbound_policy score=30 malwarescore=0
 clxscore=1011 bulkscore=0 impostorscore=0 phishscore=0 mlxscore=0
 spamscore=0 lowpriorityscore=0 mlxlogscore=658 priorityscore=1501
 adultscore=0 suspectscore=0 classifier=spam adjust=30 reason=mlx
 scancount=1 engine=8.12.0-1904300001 definitions=main-1907180041
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi,=20

I have a x86 system with Xeon CPU running Linux with preempt_rt patch (kern=
el version 4.14).=20

When a PCI device firing interrupt to GSI 44 (ioapic2, pin20), I noticed th=
at GSI 19 (ioapic1, pin19) will get fired as well, and then it went unhandl=
ed.
I can reproduce this issue by using another PCI card or swapping the PCI ca=
rd to other slot, as long as the device is driving GSI 44.

By putting traces on do_IRQ, I can see it's being called once for GSI 44, t=
hen being called another once for GSI 19.

I tried to reproduce it on RHEL 8, it is not reproducible initially. Howeve=
r, after I added "threadirqs" kernel parameter, this behaviour appears on R=
HEL 8 as well.

I would like to get your advice on whether this could be a kernel issue or =
hardware issue.
Inputs on how to further narrow down the issue are most welcomed.

Thanks very much in advance,
Kar Hin Ong