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 <[email protected]>
Tested-by: Jiri Olsa <[email protected]> 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 >
