* [PATCH] x86/stacktrace: update kconfig help text for reliable unwinders
@ 2019-11-06 22:43 Joe Lawrence
2019-11-06 23:05 ` Josh Poimboeuf
0 siblings, 1 reply; 4+ messages in thread
From: Joe Lawrence @ 2019-11-06 22:43 UTC (permalink / raw)
To: linux-kernel, live-patching; +Cc: Josh Poimboeuf
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.
+
endchoice
config FRAME_POINTER
--
2.21.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] x86/stacktrace: update kconfig help text for reliable unwinders 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 0 siblings, 1 reply; 4+ messages in thread From: Josh Poimboeuf @ 2019-11-06 23:05 UTC (permalink / raw) To: Joe Lawrence; +Cc: linux-kernel, live-patching 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 -- Josh ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86/stacktrace: update kconfig help text for reliable unwinders 2019-11-06 23:05 ` Josh Poimboeuf @ 2019-11-06 23:16 ` Joe Lawrence 2019-11-06 23:54 ` Josh Poimboeuf 0 siblings, 1 reply; 4+ messages in thread From: Joe Lawrence @ 2019-11-06 23:16 UTC (permalink / raw) To: Josh Poimboeuf; +Cc: linux-kernel, live-patching 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86/stacktrace: update kconfig help text for reliable unwinders 2019-11-06 23:16 ` Joe Lawrence @ 2019-11-06 23:54 ` Josh Poimboeuf 0 siblings, 0 replies; 4+ messages in thread From: Josh Poimboeuf @ 2019-11-06 23:54 UTC (permalink / raw) To: Joe Lawrence; +Cc: linux-kernel, live-patching On Wed, Nov 06, 2019 at 06:16:28PM -0500, Joe Lawrence wrote: > 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. The guess unwinder is listed as an expert option, so the user would have to enable CONFIG_EXPERT to get to it. Then if they do enable it and try to load a livepatch, they'll get a runtime warning along with a patch which never transitions. And like you said, nobody has complained, so I'd say just dropping the 2nd hunk would be fine. -- Josh ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-11-06 23:54 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 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 2019-11-06 23:54 ` Josh Poimboeuf
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