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Wed, 27 Jan 2021 14:25:57 +0000 From: Jianlin Lv To: Masami Hiramatsu CC: Oleg Nesterov , Steven Rostedt , "mingo@redhat.com" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH v3] tracing: precise log info for kretprobe addr err Thread-Topic: [PATCH v3] tracing: precise log info for kretprobe addr err Thread-Index: AQHW8zNhQKRvGbxdckymzuUtTURLX6o4ptSAgAAFXgCAAKEyAIABDbmAgABfZwCAAAtrAIAAtAyAgAAPwGA= Date: Wed, 27 Jan 2021 14:25:57 +0000 Message-ID: References: <20210125160108.2147511-1-Jianlin.Lv@arm.com> <20210125181926.GA10248@redhat.com> <20210125133840.511b1496@gandalf.local.home> <20210126131536.f6e3a737a7b948799084fa7a@kernel.org> <20210126202058.GC12469@redhat.com> <20210127110226.a65b3e8c66eeab6ee63f8aee@kernel.org> <20210127222743.771338cf7f89fb0b78dd838c@kernel.org> In-Reply-To: <20210127222743.771338cf7f89fb0b78dd838c@kernel.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ts-tracking-id: 192BFA20D8AD6C40BDA250D4618A2F2B.0 x-checkrecipientchecked: true Authentication-Results-Original: kernel.org; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Jan 2021 14:26:04.4372 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c6b13e3d-d83f-47fe-d7dd-08d8c2cf7aa3 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: DB5EUR03FT016.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1PR0801MB1963 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Masami Hiramatsu > Sent: Wednesday, January 27, 2021 9:28 PM > To: Jianlin Lv > Cc: Oleg Nesterov ; Steven Rostedt > ; mingo@redhat.com; linux-kernel@vger.kernel.org > Subject: Re: [PATCH v3] tracing: precise log info for kretprobe addr err > > On Wed, 27 Jan 2021 02:46:10 +0000 > Jianlin Lv wrote: > > > > > > > > -----Original Message----- > > > From: Masami Hiramatsu > > > Sent: Wednesday, January 27, 2021 10:02 AM > > > To: Oleg Nesterov > > > Cc: Steven Rostedt ; Jianlin Lv > > > ; mingo@redhat.com; linux- > kernel@vger.kernel.org > > > Subject: Re: [PATCH v3] tracing: precise log info for kretprobe addr > > > err > > > > > > On Tue, 26 Jan 2021 21:20:59 +0100 > > > Oleg Nesterov wrote: > > > > > > > On 01/26, Masami Hiramatsu wrote: > > > > > > > > > > > > > > > > > > > IOW, the "offset !=3D 0" check removed by this patch is > > > > > > > obviously wrong, > > > right? > > > > > > > > > > > > > > > > > No, not wrong. Even offset !=3D 0, if the symbol exists in the > > > > > kernel, > > > > > kprobe_on_func_entry() will check it. > > > > > > > > Yes, but unless I am totally confused... if kprobe_on_func_entry() > > > > returns false, then trace_kprobe_create() should fail with > > > > BAD_RETPROBE > > > even if offset =3D=3D 0 ? > > > > > > Yes, if kprobe_on_func_entry() returns false, register_kretprobe() > > > also returns an error. > > > > > > ----- > > > int register_kretprobe(struct kretprobe *rp) { > > > int ret =3D 0; > > > struct kretprobe_instance *inst; > > > int i; > > > void *addr; > > > > > > if (!kprobe_on_func_entry(rp->kp.addr, rp->kp.symbol_name, > > > rp- > > > >kp.offset)) > > > return -EINVAL; > > > > > > ----- > > > > > > Thank you, > > > > > > -- > > > Masami Hiramatsu > > > > > > If register_kretprobe()returns an error -EINVAL. > > This means that __register_trace_kprobe return -EINVAL, > > > > --- > > ret =3D __register_trace_kprobe(tk); > > if (ret =3D=3D -ENOENT && !trace_kprobe_module_exist(tk)) { pr_warn("Th= is > > probe might be able to register after target module is loaded. > > Continue.\n"); ret =3D 0; } > > --- > > As code show, cannot enable kretprobe for an unloaded module. > > > > This is consistent with my test results (no VXLAN module is loaded). > > > > # perf probe -m /lib/modules/5.11.0-rc2+/kernel/drivers/net/vxlan.ko > > \ 'vxlan_xmit%return $retval' > > Failed to write event: Invalid argument > > Error: Failed to add events. > > > > Is this a bug? > > Oops, good catch! > It seems that the bug has been introduced when I added > kprobe_on_func_entry() to register_Kretprobe. > Let me fix it. > > Thank you! > > > -- > Masami Hiramatsu After confirming this problem, my worries are eliminated, and the current patch will be updated later. I am also investigating this bug, and I think this process will deepen my understanding of kernel probes. Jianlin IMPORTANT NOTICE: The contents of this email and any attachments are confid= ential and may also be privileged. If you are not the intended recipient, p= lease notify the sender immediately and do not disclose the contents to any= other person, use it for any purpose, or store or copy the information in = any medium. Thank you.