On Tue, Jul 25, 2017 at 11:10:59AM +0200, Ingo Molnar wrote: > > * Josh Poimboeuf <[email protected]> wrote: > > > A couple of Kconfig changes which make it much easier to switch to the > > new CONFIG_ORC_UNWINDER: > > > > 1) Remove x86 dependencies on CONFIG_FRAME_POINTER for lockdep, > > latencytop, and fault injection. x86 has a 'guess' unwinder which > > just scans the stack for kernel text addresses. It's not 100% > > accurate but in many cases it's good enough. This allows those users > > who don't want the text overhead of the frame pointer or ORC > > unwinders to still use these features. More importantly, this also > > makes it much more straightforward to disable frame pointers. > > > > 2) Make CONFIG_ORC_UNWINDER depend on !CONFIG_FRAME_POINTER. While it > > would be possible to have both enabled, it doesn't really make sense > > to do so. So enforce a sane configuration to prevent the user from > > making a dumb mistake. > > > > With these changes, when you disable CONFIG_FRAME_POINTER, "make > > oldconfig" will ask if you want to enable CONFIG_ORC_UNWINDER. > > Yeah, so I think this is still suboptimal: the frame pointer and the Orc > unwinders > are configured in different places, and the user won't know about the various > unwinder options unless stumbling across them by accidentally disabling frame > pointers ... > > Also, the Kconfig help text for frame pointers is now actively misleading: > > CONFIG_FRAME_POINTER: > > If you say Y here the resulting kernel image will be slightly > larger and slower, but it gives very useful debugging information > in case of kernel bugs. (precise oopses/stacktraces/warnings) > > Please, as I suggested it before, make it a multiple choice option: frame, > Orc, or > the guess unwinder. > > I'd only offer the 'guess' unwinder if EXPERT is selected, because it's a > really > sub-optimal selection all things considered. > > Once things are tested and it's all rosy we can change the default x86 > unwinder to > Orc and organize the naming of the config variables to: > > CONFIG_UNWINDER_ORC > CONFIG_UNWINDER_FRAME_POINTER > CONFIG_UNWINDER_GUESS
How about the below patch? It goes on top of the other two. ---- From: Josh Poimboeuf <[email protected]> Subject: [PATCH] x86/kconfig: consolidate unwinders into multiple choice selection There are three mutually exclusive unwinders. Make that more obvious by combining them into a multiple-choice selection: CONFIG_FRAME_POINTER_UNWINDER CONFIG_ORC_UNWINDER CONFIG_GUESS_UNWINDER (if CONFIG_EXPERT=y) Frame pointers are still the default (for now). The old CONFIG_FRAME_POINTER option is still used in some arch-independent places, so keep it around, but make it invisible to the user on x86. It's now selected by CONFIG_FRAME_POINTER_UNWINDER. Suggested-by: Ingo Molnar <[email protected]> Signed-off-by: Josh Poimboeuf <[email protected]> --- arch/x86/Kconfig | 3 +-- arch/x86/Kconfig.debug | 47 ++++++++++++++++++++++++++++++++++++------- arch/x86/configs/tiny.config | 2 ++ arch/x86/include/asm/unwind.h | 4 ++-- 4 files changed, 45 insertions(+), 11 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 21c75a652bb9..1e789ecefc02 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -73,7 +73,6 @@ config X86 select ARCH_USE_QUEUED_RWLOCKS select ARCH_USE_QUEUED_SPINLOCKS select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH - select ARCH_WANT_FRAME_POINTERS select ARCH_WANTS_DYNAMIC_TASK_STRUCT select ARCH_WANTS_THP_SWAP if X86_64 select BUILDTIME_EXTABLE_SORT @@ -168,7 +167,7 @@ config X86 select HAVE_PERF_REGS select HAVE_PERF_USER_STACK_DUMP select HAVE_REGS_AND_STACK_ACCESS_API - select HAVE_RELIABLE_STACKTRACE if X86_64 && FRAME_POINTER && STACK_VALIDATION + select HAVE_RELIABLE_STACKTRACE if X86_64 && FRAME_POINTER_UNWINDER && STACK_VALIDATION select HAVE_STACK_VALIDATION if X86_64 select HAVE_SYSCALL_TRACEPOINTS select HAVE_UNSTABLE_SCHED_CLOCK diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index e6176007b838..71a48a30fc84 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -356,9 +356,32 @@ config PUNIT_ATOM_DEBUG The current power state can be read from /sys/kernel/debug/punit_atom/dev_power_state +choice + prompt "Choose kernel unwinder" + default FRAME_POINTER_UNWINDER + ---help--- + This determines which method will be used for unwinding kernel stack + traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack, + livepatch, lockdep, and more. + +config FRAME_POINTER_UNWINDER + bool "Frame pointer unwinder" + select FRAME_POINTER + ---help--- + This option enables the frame pointer unwinder for unwinding kernel + stack traces. + + The unwinder itself is fast and it uses less RAM than the ORC + 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 ORC_UNWINDER bool "ORC unwinder" - depends on X86_64 && !FRAME_POINTER + depends on X86_64 select STACK_VALIDATION ---help--- This option enables the ORC (Oops Rewind Capability) unwinder for @@ -372,12 +395,22 @@ config ORC_UNWINDER Enabling this option will increase the kernel's runtime memory usage by roughly 2-4MB, depending on your kernel config. -config FRAME_POINTER_UNWINDER - def_bool y - depends on !ORC_UNWINDER && FRAME_POINTER - config GUESS_UNWINDER - def_bool y - depends on !ORC_UNWINDER && !FRAME_POINTER + bool "Guess unwinder" + depends on EXPERT + ---help--- + This option enables the "guess" unwinder for unwinding kernel stack + traces. It scans the stack and reports every kernel text address it + finds. Some of the addresses it reports may be incorrect. + + While this option often produces false positives, it can still be + useful in many cases. Unlike the other unwinders, it has no runtime + overhead. + +endchoice + +config FRAME_POINTER + depends on !ORC_UNWINDER && !GUESS_UNWINDER + bool endmenu diff --git a/arch/x86/configs/tiny.config b/arch/x86/configs/tiny.config index 4b429df40d7a..550cd5012b73 100644 --- a/arch/x86/configs/tiny.config +++ b/arch/x86/configs/tiny.config @@ -1,3 +1,5 @@ CONFIG_NOHIGHMEM=y # CONFIG_HIGHMEM4G is not set # CONFIG_HIGHMEM64G is not set +CONFIG_GUESS_UNWINDER=y +# CONFIG_FRAME_POINTER_UNWINDER is not set diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h index 25b8d31a007d..e9f793e2df7a 100644 --- a/arch/x86/include/asm/unwind.h +++ b/arch/x86/include/asm/unwind.h @@ -16,7 +16,7 @@ struct unwind_state { bool signal, full_regs; unsigned long sp, bp, ip; struct pt_regs *regs; -#elif defined(CONFIG_FRAME_POINTER) +#elif defined(CONFIG_FRAME_POINTER_UNWINDER) bool got_irq; unsigned long *bp, *orig_sp, ip; struct pt_regs *regs; @@ -50,7 +50,7 @@ void unwind_start(struct unwind_state *state, struct task_struct *task, __unwind_start(state, task, regs, first_frame); } -#if defined(CONFIG_ORC_UNWINDER) || defined(CONFIG_FRAME_POINTER) +#if defined(CONFIG_ORC_UNWINDER) || defined(CONFIG_FRAME_POINTER_UNWINDER) static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state) { if (unwind_done(state)) -- 2.13.3
