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Thu, 18 Jun 2020 23:21:11 +0000 From: Song Liu To: Andi Kleen CC: linux-kernel , Kan Liang , Alexander Shishkin , Josh Poimboeuf , Peter Zijlstra , Tejun Heo , "Andrii Nakryiko" , Francis Ricci Subject: Re: WARNING with LBR + precise_ip=2 + bpf_get_stackid() Thread-Topic: WARNING with LBR + precise_ip=2 + bpf_get_stackid() Thread-Index: AQHWRZVzS1zA6qEPN0CAIz19Cc1kQqje9n2AgAAMpQA= Date: Thu, 18 Jun 2020 23:21:11 +0000 Message-ID: <4889871D-5E00-4E50-9089-2A18C29B8D93@fb.com> References: <20200618223555.GB793265@tassilo.jf.intel.com> In-Reply-To: <20200618223555.GB793265@tassilo.jf.intel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.80.23.2.2) authentication-results: linux.intel.com; dkim=none (message not signed) header.d=none;linux.intel.com; dmarc=none action=none header.from=fb.com; x-originating-ip: [2620:10d:c090:400::5:30b0] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 2162aec0-e7eb-416d-c179-08d813de4999 x-ms-traffictypediagnostic: BYAPR15MB2725: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-fb-source: Internal x-ms-oob-tlc-oobclassifiers: OLM:9508; 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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 2162aec0-e7eb-416d-c179-08d813de4999 X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Jun 2020 23:21:11.0296 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 0owxUwlFHX4EV3naLiJDr18B/DUTFtalKzyazbnpLFubb1+cTPv5TFgWGSfdjo12wxGAC+ilo5TSJRor8neS1Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2725 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-06-18_21:2020-06-18,2020-06-18 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 clxscore=1015 priorityscore=1501 impostorscore=0 cotscore=-2147483648 suspectscore=0 spamscore=0 lowpriorityscore=0 mlxscore=0 phishscore=0 bulkscore=0 adultscore=0 mlxlogscore=852 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006180179 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jun 18, 2020, at 3:35 PM, Andi Kleen wrote: >=20 >> We noticed that this only happens with precise_ip >=3D 2. This is caused= by=20 >> setup_pebs_fixed_sample_data() using pens->real_ip: >>=20 >> set_linear_ip(regs, pebs->real_ip); >=20 > With precise_ip =3D=3D 1 the IP will be one instruction behind. > That's the only difference to 2 or 3. >=20 > So something about the actual instruction confuses the unwinder. >=20 > I would check if there is anything special about these IPs: >=20 >> 0xfffffe00004d1f78 entry_SYSCALL_64 >> 0xfffffe00004d1fa0 entry_SYSCALL_64 >> 0xfffffe00004d1fd8 entry_SYSCALL_64 I don't have this system at the moment. For the system I have, I got: [36000.163945] WARNING: can't access registers at error_entry+0x74/0xe0 [36000.243879] WARNING: can't access registers at error_entry+0x65/0xe0 [36000.334288] WARNING: can't access registers at syscall_return_via_sysret= +0x12/0x7f [36000.540940] WARNING: can't access registers at syscall_return_via_sysret= +0x6/0x7f [58419.640387] WARNING: can't access registers at syscall_return_via_sysret= +0xb/0x7f [58423.082418] WARNING: can't access registers at syscall_return_via_sysret= +0xf/0x7f [58423.155705] WARNING: can't access registers at syscall_return_via_sysret= +0x6/0x7f And (gdb) x/5i error_entry+0x65 0xffffffff81c01075 : pop %r12 0xffffffff81c01077 : mov %rsp,%rdi 0xffffffff81c0107a : callq 0xffffffff81aa7a30 <= sync_regs> 0xffffffff81c0107f : mov %rax,%rsp 0xffffffff81c01082 : push %r12 (gdb) x/5i error_entry+0x74 0xffffffff81c01084 : retq 0xffffffff81c01085 : nop 0xffffffff81c01086 : nop 0xffffffff81c01087 : nop 0xffffffff81c01088 : retq (gdb) x/5i syscall_return_via_sysret+0xb 0xffffffff81c000ec : pop %r10 0xffffffff81c000ee : pop %r9 0xffffffff81c000f0 : pop %r8 0xffffffff81c000f2 : pop %rax 0xffffffff81c000f3 : pop %rsi (gdb) x/5i syscall_return_via_sysret+0xa 0xffffffff81c000eb : pop %rsi 0xffffffff81c000ec : pop %r10 0xffffffff81c000ee : pop %r9 0xffffffff81c000f0 : pop %r8 0xffffffff81c000f2 : pop %rax (gdb) x/5i syscall_return_via_sysret+0x12 0xffffffff81c000f3 : pop %rsi 0xffffffff81c000f4 : pop %rdx 0xffffffff81c000f5 : pop %rsi 0xffffffff81c000f6 : mov %rsp,%rdi 0xffffffff81c000f9 : mov %gs:0x6004,%rsp (gdb) x/5i syscall_return_via_sysret+0x6 0xffffffff81c000e7 : pop %r12 0xffffffff81c000e9 : pop %rbp 0xffffffff81c000ea : pop %rbx 0xffffffff81c000eb : pop %rsi 0xffffffff81c000ec : pop %r10 I am not sure whether there is anything special. Maybe "pop"? Thanks, Song