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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
Cc: Mark Brown <broonie@kernel.org>,
	mark.rutland@arm.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 14:16:08 -0500	[thread overview]
Message-ID: <20210521191608.f24sldzhpg3hyq32@treble> (raw)
In-Reply-To: <20210521191140.4aezpvm2kruztufi@treble>

On Fri, May 21, 2021 at 02:11:45PM -0500, Josh Poimboeuf wrote:
> On Fri, May 21, 2021 at 01:59:16PM -0500, Madhavan T. Venkataraman wrote:
> > 
> > 
> > On 5/21/21 1:48 PM, Josh Poimboeuf wrote:
> > > On Fri, May 21, 2021 at 06:53:18PM +0100, Mark Brown wrote:
> > >> On Fri, May 21, 2021 at 12:47:13PM -0500, Madhavan T. Venkataraman wrote:
> > >>> On 5/21/21 12:42 PM, Mark Brown wrote:
> > >>
> > >>>> 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()?
> > >>
> > >> I think it's fine to leave it as it is.
> > > 
> > > Either way works for me, but if you remove those 'reliable = false'
> > > statements for stack corruption then, IIRC, the caller would still have
> > > some confusion between the end of stack error (-ENOENT) and the other
> > > errors (-EINVAL).
> > > 
> > 
> > I will leave it the way it is. That is, I will do reliable = false on errors
> > like you suggested.
> > 
> > > So the caller would have to know that -ENOENT really means success.
> > > Which, to me, seems kind of flaky.
> > > 
> > 
> > Actually, that is why -ENOENT was introduced - to indicate successful
> > stack trace termination. A return value of 0 is for continuing with
> > the stack trace. A non-zero value is for terminating the stack trace.
> > 
> > So, either we return a positive value (say 1) to indicate successful
> > termination. Or, we return -ENOENT to say no more stack frames left.
> > I guess -ENOENT was chosen.
> 
> I see.  So it's a tri-state return value, and frame->reliable is
> intended to be a private interface not checked by the callers.

Or is frame->reliable supposed to be checked after all?  Looking at the
code again, I'm not sure.

Either way it would be good to document the interface more clearly in a
comment above the function.

-- 
Josh


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  reply	other threads:[~2021-05-21 19:18 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <68eeda61b3e9579d65698a884b26c8632025e503>
2021-05-16  4:00 ` [RFC PATCH v4 0/2] arm64: Stack " madvenka
2021-05-16  4:00   ` [RFC PATCH v4 1/2] arm64: Introduce stack " madvenka
2021-05-21 16:11     ` Mark Brown
2021-05-21 17:23       ` Madhavan T. Venkataraman
2021-05-21 17:42         ` Mark Brown
2021-05-21 17:47           ` Madhavan T. Venkataraman
2021-05-21 17:53             ` Mark Brown
2021-05-21 18:48               ` Josh Poimboeuf
2021-05-21 18:59                 ` Madhavan T. Venkataraman
2021-05-21 19:11                   ` Josh Poimboeuf
2021-05-21 19:16                     ` Josh Poimboeuf [this message]
2021-05-21 19:41                       ` Madhavan T. Venkataraman
2021-05-21 20:08                         ` Josh Poimboeuf
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
2021-05-19  2:06     ` nobuta.keiya
2021-05-19  3:38       ` Madhavan T. Venkataraman
2021-05-19 19:27     ` Mark Brown
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 17:32     ` Madhavan T. Venkataraman
2021-05-21 17:47       ` Mark Brown
2021-05-21 17:48         ` Madhavan T. Venkataraman

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