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Tue, 16 Mar 2021 22:46:22 +0900 (KST) Received: from localhost.localdomain (unknown [10.253.105.183]) by epsmtip1.samsung.com (KnoxPortal) with ESMTPA id 20210316134622epsmtip109e67ba22e6c219321c28e98ddc06c7d~s1qez4jZ83042430424epsmtip1Q; Tue, 16 Mar 2021 13:46:22 +0000 (GMT) From: Sangmoon Kim To: broonie@kernel.org Cc: 0x7f454c46@gmail.com, Dave.Martin@arm.com, amit.kachhap@arm.com, catalin.marinas@arm.com, gshan@redhat.com, jordan.lim@samsung.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, mingo@redhat.com, pcc@google.com, rostedt@goodmis.org, sangmoon.kim@samsung.com, will@kernel.org Subject: Re: [PATCH] arm64: traps: add tracepoints for unusal exception cases Date: Tue, 16 Mar 2021 22:37:20 +0900 Message-Id: <20210316133720.9432-1-sangmoon.kim@samsung.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20210308133149.GA4656@sirena.org.uk> X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprGJsWRmVeSWpSXmKPExsWy7bCmru66bQEJBndvmFhMmPaCxWLKhx2s FlMfPmGzeL+sh9Giae4eRouXu7YxWdxYFmax6fE1VovLu+awWSy9fpHJ4tKBBUwW/Xeus1ns 63jAZHHrQSOLRcsdUwd+jzXz1jB67Jx1l92jZd8tdo8Fm0o9Nq3qZPPYvKTe4/2+q2wefVtW MXp83iQXwBmVY5ORmpiSWqSQmpecn5KZl26r5B0c7xxvamZgqGtoaWGupJCXmJtqq+TiE6Dr lpkDdL6SQlliTilQKCCxuFhJ386mKL+0JFUhI7+4xFYptSAlp8DQoECvODG3uDQvXS85P9fK 0MDAyBSoMiEn48fLeSwF70UrZny7ydLAuE6wi5GTQ0LAROL9h0+sXYxcHEICOxgl7v49zA7h fGKUeHt+P5TzjVFi3ekpjDAt594+BrOFBPYySuydJAxR9IVR4tuaV2wgCTYBXYkv8y6DFYkI iEncntPJDFLELHCKSeLa/cfsIAlhAX+Jkw1rmUBsFgFViYl3DgLFOTh4BWwkDp4qhlgmL7F6 wwFmEJtTwEjiwpbNbCBzJAQWckjs2r4J6iIXiTlTvzND2MISr45vYYewpSQ+v9vLBmHvY5TY s1IGonkKo8TyKTugiowlensuMIMsZhbQlFi/Sx8irCix8/dcsPnMAnwS7772sIKUSAjwSnS0 CUGUqEk8fnUX6gQZif4781kgbA+JiX8vs0ECpZVRYlnfWdYJjHKzEDYsYGRcxSiWWlCcm55a bFhgghxlmxjBCVTLYgfj3Lcf9A4xMnEwHmKU4GBWEuE1zQtIEOJNSaysSi3Kjy8qzUktPsRo Cgy8icxSosn5wBSeVxJvaGpkbGxsYWJmbmZqrCTOm2TwIF5IID2xJDU7NbUgtQimj4mDU6qB Ke9A+aWrRQdFg96Fnj6kn7jNPGtj54zmpOunr1t6bb8bOo37xPc35zrfL4n1eKtiZLxSu3rt iis31lY3bd8S7clzo+J5/09Fnu6NARtn+VwRnRmTcf/bC27Newf1jBI3+PPrcDS27O5Yc+Nq VG+Mzr6IgqVr5cRETWaxtWtsv6UiKXPv75Y7UTE/zKeLbBF68ld5zqLJ+TwxOz/u8F4od/je caGQLZ43TrCLbq5ouJj8Kkvgfy5r8q6G6rLjOV4TTZnyl8s1FanG6kj8fPLrY339QtnN+tZW xXMuJkxL61h287bZJNGu4E7DNvWGF2n7PwX+OCLAraHD3CDnsuWd8EHG1/Wid/2rNvX1rd3u o8RSnJFoqMVcVJwIAISG+MUpBAAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFjrHLMWRmVeSWpSXmKPExsWy7bCSnO66bQEJBp9beS0mTHvBYjHlww5W i6kPn7BZvF/Ww2jRNHcPo8XLXduYLG4sC7PY9Pgaq8XlXXPYLJZev8hkcenAAiaL/jvX2Sz2 dTxgsrj1oJHFouWOqQO/x5p5axg9ds66y+7Rsu8Wu8eCTaUem1Z1snlsXlLv8X7fVTaPvi2r GD0+b5IL4IzisklJzcksSy3St0vgyvjxch5LwXvRihnfbrI0MK4T7GLk5JAQMJE49/YxYxcj F4eQwG5GiWvLWpggEjISOy9uBrI5gGxhicOHiyFqPjFKtN1+zgJSwyagK/Fl3mVGEFtEQEzi 9pxOZpAiZoE7TBLPPrxnB0kIC/hK7J+9jRXEZhFQlZh45yA7yFBeARuJg6eKIXbJS6zecIAZ xOYUMJK4sGUzG4gtJGAoMen7JZYJjHwLGBlWMUqmFhTnpucWGxYY5qWW6xUn5haX5qXrJefn bmIEB7mW5g7G7as+6B1iZOJgPMQowcGsJMJrmheQIMSbklhZlVqUH19UmpNafIhRmoNFSZz3 QtfJeCGB9MSS1OzU1ILUIpgsEwenVAOTrgBv3CuDxJNBb8LvTtK/2TI5XK3wU1qeuMLEBmf2 blGOGYKbleqfO4Ud77W9xrGS5birdkiPU6tXi61r646+/RHJR5Qezf5Y7fhgTcw6My3T3+Em LK2HdaceYHxqnpC//u+m0oKQRNPylD+ekv9OrZv3symzwV85cYGz/p+vylJ1RuGl2h6aWyw/ fKxMMC5MNHn2uTrfdtmG3YmWb/a/t9lx1J1ht+AfbskZ097cDj0wb7GsccWkve8Dbc/410ky +V7ZsP5/zNIqzu+NG2Y+/BIfrRPQNdP8Qv9VboWFL/5tiikUYAk98tC+3maa6r/ZB7/paZeJ MSh6c2j4LWf4u/SEoO9K2dyP8xbuKFNiKc5INNRiLipOBABYQkyt4QIAAA== X-CMS-MailID: 20210316134622epcas1p488fe019ee343dd156dc077c6df9322da X-Msg-Generator: CA X-Sendblock-Type: SVC_REQ_APPROVE CMS-TYPE: 101P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20210316134622epcas1p488fe019ee343dd156dc077c6df9322da References: <20210308133149.GA4656@sirena.org.uk> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210316_134633_423081_3FA0E5A0 X-CRM114-Status: GOOD ( 36.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > -----Original Message----- > From: Mark Brown > Sent: Monday, March 8, 2021 10:32 PM > Subject: Re: [PATCH] arm64: traps: add tracepoints for unusal exception cases > > On Fri, Mar 05, 2021 at 09:36:30PM +0900, Sangmoon Kim wrote: > > > When kernel panic occurs, a kernel module can use either the > > panic_notifier or die_notifier to obtain the debugging information. > > > However, in case of these exceptions like do_undefinstr(), regs and > > esr data are not passed on. Although a module might be able to find > > those data in the console messages, parsing text messages is very > > expensive behavior for a module especially on mobile devices. > > > These bare tracepoints allow a module to probe regs and esr information > > for debugging purpose. _tp suffix comes from bare tracepoints of > > sched/core.c > > This use case sounds a lot like what the enterprise and Android people > do via pstore - it seems like it would be better for this to integrate > via the interfaces that other systems are using for similar purposes and > then ensure that whatever information is useful is getting passed > through in a format that makes sense. That'd be more structured and > more readily usable by a wider range of systems than something that's > more of a building block, going via the trace infrastructure seems like > a bit of an indirection. > > > @@ -832,6 +846,7 @@ void __noreturn arm64_serror_panic(struct pt_regs *regs, u32 esr) > > if (regs) > > __show_regs(regs); > > > > + trace_traps_serror_panic_tp(regs, esr); > > nmi_panic(regs, "Asynchronous SError Interrupt"); > > One of the concerns people have with adding tracepoints is that they can > end up defining ABI so if we *are* going to add any then we need to > think carefully about how they're defined. As things currently stand > they'll pass in the full pt_regs struct which includes not only what's > defined by the hardware but also additional software defined information > we store along with it like the stackframe which would be even more of a > problem if it ends up getting used by someone in a way that ends up as > ABI. These are defined as bare tracehooks which does mitigate against > things ending up getting used in ways that cause problems but people are > still going to worry about things ending up getting relied on one way or > another. > > That said it's not clear to me that this will record anything beyond the > pointer directly in the trace buffer so the value might not be useful > for terribly long, that itself feels like it might not be as robust an > interface as it should be. Dear Mark, Thank you for your review. I learned a lot about the concerns when using tracepoint. Thanks, Sangmoon _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel