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SubjectRe: [RFC PATCH v2] perf/x86: make perf callchain work without CONFIG_FRAME_POINTER
On Tue, Apr 09, 2019 at 12:59:42AM +0800, Kairui Song wrote:
> Currently perf callchain is not working properly with ORC unwinder,
> and sampling event from trace point. We'll get useless in kernel
> callchain like this:
>
> perf 6429 [000] 22.498450: kmem:mm_page_alloc: page=0x176a17 pfn=1534487 order=0 migratetype=0 gfp_flags=GFP_KERNEL
> ffffffffbe23e32e __alloc_pages_nodemask+0x22e (/lib/modules/5.1.0-rc3+/build/vmlinux)
> 7efdf7f7d3e8 __poll+0x18 (/usr/lib64/libc-2.28.so)
> 5651468729c1 [unknown] (/usr/bin/perf)
> 5651467ee82a main+0x69a (/usr/bin/perf)
> 7efdf7eaf413 __libc_start_main+0xf3 (/usr/lib64/libc-2.28.so)
> 5541f689495641d7 [unknown] ([unknown])
>
> The root cause is within a trace point perf will try to dump the
> caller's register, but without CONFIG_FRAME_POINTER we can't get
> caller's BP as the frame pointer, so current frame pointer is returned
> instead. We get a register combination of caller IP and current BP,
> which confuse the unwinder and end the stacktrace early.
>
> So in such case don't dump BP, and just let the unwinder start directly
> and skip until we reached the stack we wanted.
>
> This make the callchain get the full kernel space stacktrace again:
>
> perf 6503 [000] 1567.570191: kmem:mm_page_alloc: page=0x16c904 pfn=1493252 order=0 migratetype=0 gfp_flags=GFP_KERNEL
> ffffffffb523e2ae __alloc_pages_nodemask+0x22e (/lib/modules/5.1.0-rc3+/build/vmlinux)
> ffffffffb52383bd __get_free_pages+0xd (/lib/modules/5.1.0-rc3+/build/vmlinux)
> ffffffffb52fd28a __pollwait+0x8a (/lib/modules/5.1.0-rc3+/build/vmlinux)
> ffffffffb521426f perf_poll+0x2f (/lib/modules/5.1.0-rc3+/build/vmlinux)
> ffffffffb52fe3e2 do_sys_poll+0x252 (/lib/modules/5.1.0-rc3+/build/vmlinux)
> ffffffffb52ff027 __x64_sys_poll+0x37 (/lib/modules/5.1.0-rc3+/build/vmlinux)
> ffffffffb500418b do_syscall_64+0x5b (/lib/modules/5.1.0-rc3+/build/vmlinux)
> ffffffffb5a0008c entry_SYSCALL_64_after_hwframe+0x44 (/lib/modules/5.1.0-rc3+/build/vmlinux)
> 7f71e92d03e8 __poll+0x18 (/usr/lib64/libc-2.28.so)
> 55a22960d9c1 [unknown] (/usr/bin/perf)
> 55a22958982a main+0x69a (/usr/bin/perf)
> 7f71e9202413 __libc_start_main+0xf3 (/usr/lib64/libc-2.28.so)
> 5541f689495641d7 [unknown] ([unknown])
>
> Signed-off-by: Kairui Song <kasong@redhat.com>

Tested-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> ---
>
> Update from V1:
> Get rid of a lot of unneccessary code and just don't dump a inaccurate
> BP, and use SP as the marker for target frame.
>
> arch/x86/events/core.c | 18 +++++++++++++++---
> arch/x86/include/asm/stacktrace.h | 9 +++++++--
> 2 files changed, 22 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index e2b1447192a8..6075a4f94376 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2355,6 +2355,12 @@ void arch_perf_update_userpage(struct perf_event *event,
> cyc2ns_read_end();
> }
>
> +static inline int
> +valid_perf_registers(struct pt_regs *regs)
> +{
> + return (regs->ip && regs->bp && regs->sp);
> +}
> +
> void
> perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
> {
> @@ -2366,11 +2372,17 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
> return;
> }
>
> - if (perf_callchain_store(entry, regs->ip))
> + if (valid_perf_registers(regs)) {
> + if (perf_callchain_store(entry, regs->ip))
> + return;
> + unwind_start(&state, current, regs, NULL);
> + } else if (regs->sp) {
> + unwind_start(&state, current, NULL, (unsigned long *)regs->sp);
> + } else {
> return;
> + }
>
> - for (unwind_start(&state, current, regs, NULL); !unwind_done(&state);
> - unwind_next_frame(&state)) {
> + for (; !unwind_done(&state); unwind_next_frame(&state)) {
> addr = unwind_get_return_address(&state);
> if (!addr || perf_callchain_store(entry, addr))
> return;
> diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
> index f335aad404a4..226077e20412 100644
> --- a/arch/x86/include/asm/stacktrace.h
> +++ b/arch/x86/include/asm/stacktrace.h
> @@ -98,18 +98,23 @@ struct stack_frame_ia32 {
> u32 return_address;
> };
>
> +#ifdef CONFIG_FRAME_POINTER
> static inline unsigned long caller_frame_pointer(void)
> {
> struct stack_frame *frame;
>
> frame = __builtin_frame_address(0);
>
> -#ifdef CONFIG_FRAME_POINTER
> frame = frame->next_frame;
> -#endif
>
> return (unsigned long)frame;
> }
> +#else
> +static inline unsigned long caller_frame_pointer(void)
> +{
> + return 0;
> +}
> +#endif
>
> void show_opcodes(struct pt_regs *regs, const char *loglvl);
> void show_ip(struct pt_regs *regs, const char *loglvl);
> --
> 2.20.1
>

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