From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com> To: Mark Brown <broonie@kernel.org> Cc: mark.rutland@arm.com, jpoimboe@redhat.com, ardb@kernel.org, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v4 1/2] arm64: Introduce stack trace reliability checks in the unwinder Date: Fri, 21 May 2021 12:47:13 -0500 [thread overview] Message-ID: <26c33633-029e-6374-16e6-e9418099da95@linux.microsoft.com> (raw) In-Reply-To: <20210521174242.GD5825@sirena.org.uk> On 5/21/21 12:42 PM, Mark Brown wrote: > On Fri, May 21, 2021 at 12:23:52PM -0500, Madhavan T. Venkataraman wrote: >> On 5/21/21 11:11 AM, Mark Brown wrote: >>> On Sat, May 15, 2021 at 11:00:17PM -0500, madvenka@linux.microsoft.com wrote: > >>>> + frame->reliable = true; > >>> All these checks are good checks but as you say there's more stuff that >>> we need to add (like your patch 2 here) so I'm slightly nervous about > >> OK. So how about changing the field from a flag to an enum that says exactly >> what happened with the frame? > > TBH I think the code is fine, or rather will be fine when it gets as far > as actually being used - this was more a comment about when we flip this > switch. > OK. >> Also, the caller can get an exact idea of why the stack trace failed. > > I'm not sure anything other than someone debugging things will care > enough to get the code out and then decode it so it seems like it'd be > more trouble than it's worth, we're unlikely to be logging the code as > standard. > OK. >>> The other thing I guess is the question of if we want to bother flagging >>> frames as unrelaible when we return an error; I don't see an issue with >>> it and it may turn out to make it easier to do something in the future >>> so I'm fine with that > >> Initially, I thought that there is no need to flag it for errors. But Josh >> had a comment that the stack trace is indeed unreliable on errors. Again, the >> word unreliable is the one causing the problem. > > My understanding there is that arch_stack_walk_reliable() should be > returning an error if either the unwinder detected an error or if any > frame in the stack is flagged as unreliable so from the point of view of > users it's just looking at the error code, it's more that there's no > need for arch_stack_walk_reliable() to consider the reliability > information if an error has been detected and nothing else looks at the > reliability information. > > Like I say we may come up with some use for the flag in error cases in > future so I'm not opposed to keeping the accounting there. > So, should I leave it the way it is now? Or should I not set reliable = false for errors? Which one do you prefer? Josh, Are you OK with not flagging reliable = false for errors in unwind_frame()? Madhavan
WARNING: multiple messages have this Message-ID (diff)
From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com> To: Mark Brown <broonie@kernel.org> Cc: mark.rutland@arm.com, jpoimboe@redhat.com, ardb@kernel.org, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v4 1/2] arm64: Introduce stack trace reliability checks in the unwinder Date: Fri, 21 May 2021 12:47:13 -0500 [thread overview] Message-ID: <26c33633-029e-6374-16e6-e9418099da95@linux.microsoft.com> (raw) In-Reply-To: <20210521174242.GD5825@sirena.org.uk> On 5/21/21 12:42 PM, Mark Brown wrote: > On Fri, May 21, 2021 at 12:23:52PM -0500, Madhavan T. Venkataraman wrote: >> On 5/21/21 11:11 AM, Mark Brown wrote: >>> On Sat, May 15, 2021 at 11:00:17PM -0500, madvenka@linux.microsoft.com wrote: > >>>> + frame->reliable = true; > >>> All these checks are good checks but as you say there's more stuff that >>> we need to add (like your patch 2 here) so I'm slightly nervous about > >> OK. So how about changing the field from a flag to an enum that says exactly >> what happened with the frame? > > TBH I think the code is fine, or rather will be fine when it gets as far > as actually being used - this was more a comment about when we flip this > switch. > OK. >> Also, the caller can get an exact idea of why the stack trace failed. > > I'm not sure anything other than someone debugging things will care > enough to get the code out and then decode it so it seems like it'd be > more trouble than it's worth, we're unlikely to be logging the code as > standard. > OK. >>> The other thing I guess is the question of if we want to bother flagging >>> frames as unrelaible when we return an error; I don't see an issue with >>> it and it may turn out to make it easier to do something in the future >>> so I'm fine with that > >> Initially, I thought that there is no need to flag it for errors. But Josh >> had a comment that the stack trace is indeed unreliable on errors. Again, the >> word unreliable is the one causing the problem. > > My understanding there is that arch_stack_walk_reliable() should be > returning an error if either the unwinder detected an error or if any > frame in the stack is flagged as unreliable so from the point of view of > users it's just looking at the error code, it's more that there's no > need for arch_stack_walk_reliable() to consider the reliability > information if an error has been detected and nothing else looks at the > reliability information. > > Like I say we may come up with some use for the flag in error cases in > future so I'm not opposed to keeping the accounting there. > So, should I leave it the way it is now? Or should I not set reliable = false for errors? Which one do you prefer? Josh, Are you OK with not flagging reliable = false for errors in unwind_frame()? Madhavan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-05-21 17:47 UTC|newest] Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <68eeda61b3e9579d65698a884b26c8632025e503> 2021-05-16 4:00 ` [RFC PATCH v4 0/2] arm64: Stack trace reliability checks in the unwinder madvenka 2021-05-16 4:00 ` madvenka 2021-05-16 4:00 ` [RFC PATCH v4 1/2] arm64: Introduce stack " madvenka 2021-05-16 4:00 ` madvenka 2021-05-21 16:11 ` Mark Brown 2021-05-21 16:11 ` Mark Brown 2021-05-21 17:23 ` Madhavan T. Venkataraman 2021-05-21 17:23 ` Madhavan T. Venkataraman 2021-05-21 17:42 ` Mark Brown 2021-05-21 17:42 ` Mark Brown 2021-05-21 17:47 ` Madhavan T. Venkataraman [this message] 2021-05-21 17:47 ` Madhavan T. Venkataraman 2021-05-21 17:53 ` Mark Brown 2021-05-21 17:53 ` Mark Brown 2021-05-21 18:48 ` Josh Poimboeuf 2021-05-21 18:48 ` Josh Poimboeuf 2021-05-21 18:59 ` Madhavan T. Venkataraman 2021-05-21 18:59 ` Madhavan T. Venkataraman 2021-05-21 19:11 ` Josh Poimboeuf 2021-05-21 19:11 ` Josh Poimboeuf 2021-05-21 19:16 ` Josh Poimboeuf 2021-05-21 19:16 ` Josh Poimboeuf 2021-05-21 19:41 ` Madhavan T. Venkataraman 2021-05-21 19:41 ` Madhavan T. Venkataraman 2021-05-21 20:08 ` Josh Poimboeuf 2021-05-21 20:08 ` Josh Poimboeuf 2021-05-25 21:44 ` Madhavan T. Venkataraman 2021-05-25 21:44 ` Madhavan T. Venkataraman 2021-05-16 4:00 ` [RFC PATCH v4 2/2] arm64: Create a list of SYM_CODE functions, blacklist them " madvenka 2021-05-16 4:00 ` madvenka 2021-05-19 2:06 ` nobuta.keiya 2021-05-19 2:06 ` nobuta.keiya 2021-05-19 3:38 ` Madhavan T. Venkataraman 2021-05-19 3:38 ` Madhavan T. Venkataraman 2021-05-19 19:27 ` Mark Brown 2021-05-19 19:27 ` Mark Brown 2021-05-20 2:00 ` Madhavan T. Venkataraman 2021-05-20 2:00 ` Madhavan T. Venkataraman 2021-05-21 17:18 ` [RFC PATCH v4 0/2] arm64: Stack trace reliability checks " Mark Brown 2021-05-21 17:18 ` Mark Brown 2021-05-21 17:32 ` Madhavan T. Venkataraman 2021-05-21 17:32 ` Madhavan T. Venkataraman 2021-05-21 17:47 ` Mark Brown 2021-05-21 17:47 ` Mark Brown 2021-05-21 17:48 ` Madhavan T. Venkataraman 2021-05-21 17:48 ` Madhavan T. Venkataraman
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