From: Joe Lawrence <joe.lawrence@redhat.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-kernel@vger.kernel.org, live-patching@vger.kernel.org
Subject: Re: [PATCH] x86/stacktrace: update kconfig help text for reliable unwinders
Date: Wed, 6 Nov 2019 18:16:28 -0500 [thread overview]
Message-ID: <c8bae684-2a46-68e6-dc43-a8c215bdd111@redhat.com> (raw)
In-Reply-To: <20191106230553.wnyltmkzwk5dph4l@treble>
On 11/6/19 6:05 PM, Josh Poimboeuf wrote:
> On Wed, Nov 06, 2019 at 05:43:44PM -0500, Joe Lawrence wrote:
>> commit 6415b38bae26 ("x86/stacktrace: Enable HAVE_RELIABLE_STACKTRACE
>> for the ORC unwinder") marked the ORC unwinder as a "reliable" unwinder.
>> Update the help text to reflect that change: the frame pointer unwinder
>> is no longer the only one that provides HAVE_RELIABLE_STACKTRACE.
>>
>> Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
>> ---
>> arch/x86/Kconfig.debug | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
>> index bf9cd83de777..69cdf0558c13 100644
>> --- a/arch/x86/Kconfig.debug
>> +++ b/arch/x86/Kconfig.debug
>> @@ -316,10 +316,6 @@ config UNWINDER_FRAME_POINTER
>> unwinder, but the kernel text size will grow by ~3% and the kernel's
>> overall performance will degrade by roughly 5-10%.
>>
>> - This option is recommended if you want to use the livepatch
>> - consistency model, as this is currently the only way to get a
>> - reliable stack trace (CONFIG_HAVE_RELIABLE_STACKTRACE).
>> -
>> config UNWINDER_GUESS
>> bool "Guess unwinder"
>> depends on EXPERT
>> @@ -333,6 +329,10 @@ config UNWINDER_GUESS
>> useful in many cases. Unlike the other unwinders, it has no runtime
>> overhead.
>>
>> + This option is not recommended if you want to use the livepatch
>> + consistency model, as this unwinder cannot guarantee reliable stack
>> + traces.
>> +
>
> I'm not sure whether this last hunk is helpful. At the very least the
> wording of "not recommended" might be confusing because it's not even
> possible to combine UNWINDER_GUESS+HAVE_RELIABLE_STACKTRACE.
>
> arch/x86/Kconfig: select HAVE_RELIABLE_STACKTRACE if X86_64 && (UNWINDER_FRAME_POINTER || UNWINDER_ORC) && STACK_VALIDATION
>
Ah good point. The alternative would be to copy the recommended note to
both UNWINDER_FRAME_POINTER and UNWINDER_ORC, or at least remove the
"only" phrasing. I dunno, nobody has noticed it yet, so maybe the first
hunk would be good enough.
-- Joe
next prev parent reply other threads:[~2019-11-06 23:16 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 22:43 [PATCH] x86/stacktrace: update kconfig help text for reliable unwinders Joe Lawrence
2019-11-06 23:05 ` Josh Poimboeuf
2019-11-06 23:16 ` Joe Lawrence [this message]
2019-11-06 23:54 ` Josh Poimboeuf
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