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Mon, 16 Aug 2021 13:26:29 +0000 From: Chuck Lever III To: Timo Rothenpieler CC: Linux NFS Mailing List , Olga Kornievskaia , Dai Ngo Subject: Re: Spurious instability with NFSoRDMA under moderate load Thread-Topic: Spurious instability with NFSoRDMA under moderate load Thread-Index: AQHXSnp8j8N6G2OhyUK9Nr2RtJxnoarn3hgAgAATb4CANuhZgIBOXZcAgAAVhICAADVLgIAASYeAgAAo1oCAAAOTXYAA6JWAgAADg4CAAANlAIAAA4eAgAAZh4CAABNpAIABnm2AgAX5FgA= Date: Mon, 16 Aug 2021 13:26:29 +0000 Message-ID: <716B2A38-9705-41D7-969B-665EF90156C7@oracle.com> References: <4da3b074-a6be-d83f-ccd4-b151557066aa@rothenpieler.org> <72ECF9E1-1F6E-44AF-850C-536BED898DDD@oracle.com> <9355de20-921c-69e0-e5a4-733b64e125e1@rothenpieler.org> <4BA2A532-9063-4893-AF53-E1DAB06095CC@oracle.com> <141fdf51-2aa1-6614-fe4e-96f168cbe6cf@rothenpieler.org> <99DFF0B0-FE0F-4416-B3F6-1F9535884F39@oracle.com> <64F9A492-44B9-4057-ABA5-C8202828A8DD@oracle.com> <1b8a24a9-5dba-3faf-8b0a-16e728a6051c@rothenpieler.org> <5DD80ADC-0A4B-4D95-8CF7-29096439DE9D@oracle.com> <0444ca5c-e8b6-1d80-d8a5-8469daa74970@rothenpieler.org> <3AF4F6CA-8B17-4AE9-82E2-21A2B9AA0774@oracle.com> <4caff277-8e53-3c75-70c1-8938b2a26933@rothenpieler.org> In-Reply-To: <4caff277-8e53-3c75-70c1-8938b2a26933@rothenpieler.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: rothenpieler.org; 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charset="us-ascii" Content-ID: <00446C63CCC2B748800EDE30FEDBF131@namprd10.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SJ0PR10MB4688.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 971f70f4-4e45-40dc-eaf2-08d960b974ab X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Aug 2021 13:26:29.0732 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: oSKh5ZQRP2n6sISCE/4poaMlGdkwOkm9xSX7LwE+jmASiaWzSEft7aedHLnk8wSUycAl3DRViMyy4KkXQ5DtNQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR10MB3222 X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10077 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 adultscore=0 bulkscore=0 suspectscore=0 mlxlogscore=999 phishscore=0 mlxscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108160084 X-Proofpoint-ORIG-GUID: ENZZ8OFwh_d1qQeg5kyI0DfK5dnRmjxS X-Proofpoint-GUID: ENZZ8OFwh_d1qQeg5kyI0DfK5dnRmjxS Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org > On Aug 12, 2021, at 2:13 PM, Timo Rothenpieler wr= ote: >=20 > On 11.08.2021 19:30, Chuck Lever III wrote: >>> On Aug 11, 2021, at 12:20 PM, Timo Rothenpieler = wrote: >>>=20 >>> resulting dmesg and trace logs of both client and server are attached. >>>=20 >>> Test procedure: >>>=20 >>> - start tracing on client and server >>> - mount NFS on client >>> - immediately run 'xfs_io -fc "copy_range testfile" testfile.copy' (whi= ch succeeds) >>> - wait 10~15 minutes for the backchannel to time out (still running 5.1= 2.19 with the fix for that reverted) >>> - run xfs_io command again, getting stuck now >>> - let it sit there stuck for a minute, then cancel it >>> - run the command again >>> - while it's still stuck, finished recording the logs and traces >> The server tries to send CB_OFFLOAD when the offloaded copy >> completes, but finds the backchannel transport is not connected. >> The server can't report the problem until the client sends a >> SEQUENCE operation, but there's really no other traffic going >> on, so it just waits. >> The client eventually sends a singleton SEQUENCE to renew its >> lease. The server replies with the SEQ4_STATUS_BACKCHANNEL_FAULT >> flag set at that point. Client's recovery is to destroy that >> session and create a new one. That appears to be successful. >=20 > If it re-created the session and the backchannel, shouldn't that mean tha= t after I cancel the first stuck xfs_io command, and try it again immediate= ly (before the backchannel had a chance to timeout again) it should work? I would guess that yes, subsequent COPY_OFFLOAD requests should work unless the backchannel has already timed out again. I was about to use your reproducer myself, but a storm came through on Thursday and knocked out my power and internet. I'm still waiting for restoration. Once power is restored I can chase this a little more efficiently in my lab. > Cause that's explicitly not the case, once the backchannel initially time= s out, all subsequent commands get stuck, even if the system is seeing othe= r work on the NFS mount being done in parallel, and no matter how often I r= e-try and how long I wait in between or with it stuck. >=20 >> But the server doesn't send another CB_OFFLOAD to let the client >> know the copy is complete, so the client hangs. >> This seems to be peculiar to COPY_OFFLOAD, but I wonder if the >> other CB operations suffer from the same "failed to retransmit >> after the CB path is restored" issue. It might not matter for >> some of them, but for others like CB_RECALL, that could be >> important. >> -- >> Chuck Lever -- Chuck Lever