Re: [PATCH] perf tools: Fix crash with non-jited bpf progs

From: Jiri Olsa
Date: Mon Oct 19 2020 - 16:53:54 EST


On Fri, Oct 16, 2020 at 02:47:18PM +0300, Tommi Rantala wrote:
> The addr in PERF_RECORD_KSYMBOL events for non-jited bpf progs points to
> the bpf interpreter, ie. within kernel text section. When processing the
> unregister event, this causes unexpected removal of vmlinux_map,
> crashing perf later in cleanup:
>
> # perf record -- timeout --signal=INT 2s /usr/share/bcc/tools/execsnoop
> PCOMM PID PPID RET ARGS
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.208 MB perf.data (5155 samples) ]
> perf: tools/include/linux/refcount.h:131: refcount_sub_and_test: Assertion `!(new > val)' failed.
> Aborted (core dumped)
>
> # perf script -D|grep KSYM
> 0 0xa40 [0x48]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b530 len 0 type 1 flags 0x0 name bpf_prog_f958f6eb72ef5af6
> 0 0xab0 [0x48]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b530 len 0 type 1 flags 0x0 name bpf_prog_8c42dee26e8cd4c2
> 0 0xb20 [0x48]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b530 len 0 type 1 flags 0x0 name bpf_prog_f958f6eb72ef5af6
> 108563691893 0x33d98 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b3b0 len 0 type 1 flags 0x0 name bpf_prog_bc5697a410556fc2_syscall__execve
> 108568518458 0x34098 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b3f0 len 0 type 1 flags 0x0 name bpf_prog_45e2203c2928704d_do_ret_sys_execve
> 109301967895 0x34830 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b3b0 len 0 type 1 flags 0x1 name bpf_prog_bc5697a410556fc2_syscall__execve
> 109302007356 0x348b0 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b3f0 len 0 type 1 flags 0x1 name bpf_prog_45e2203c2928704d_do_ret_sys_execve
> perf: tools/include/linux/refcount.h:131: refcount_sub_and_test: Assertion `!(new > val)' failed.
>
> Here the addresses match the bpf interpreter:
>
> # grep -e ffffffffa9b6b530 -e ffffffffa9b6b3b0 -e ffffffffa9b6b3f0 /proc/kallsyms
> ffffffffa9b6b3b0 t __bpf_prog_run224
> ffffffffa9b6b3f0 t __bpf_prog_run192
> ffffffffa9b6b530 t __bpf_prog_run32
>
> Fix by not allowing vmlinux_map to be removed by PERF_RECORD_KSYMBOL
> unregister event.
>
> Signed-off-by: Tommi Rantala <tommi.t.rantala@xxxxxxxxx>

nice, I almost forgot about non jit mode by now ;-)

Acked/Tested-by: Jiri Olsa <jolsa@xxxxxxxxxx>

thanks,
jirka

> ---
> tools/perf/util/machine.c | 11 ++++++++++-
> tools/perf/util/symbol.c | 7 +++++++
> tools/perf/util/symbol.h | 2 ++
> 3 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 85587de027a5..d93d35463c61 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -786,11 +786,20 @@ static int machine__process_ksymbol_unregister(struct machine *machine,
> union perf_event *event,
> struct perf_sample *sample __maybe_unused)
> {
> + struct symbol *sym;
> struct map *map;
>
> map = maps__find(&machine->kmaps, event->ksymbol.addr);
> - if (map)
> + if (!map)
> + return 0;
> +
> + if (map != machine->vmlinux_map)
> maps__remove(&machine->kmaps, map);
> + else {
> + sym = dso__find_symbol(map->dso, map->map_ip(map, map->start));
> + if (sym)
> + dso__delete_symbol(map->dso, sym);
> + }
>
> return 0;
> }
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 5151a8c0b791..6bf8e74ea1d1 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -515,6 +515,13 @@ void dso__insert_symbol(struct dso *dso, struct symbol *sym)
> }
> }
>
> +void dso__delete_symbol(struct dso *dso, struct symbol *sym)
> +{
> + rb_erase_cached(&sym->rb_node, &dso->symbols);
> + symbol__delete(sym);
> + dso__reset_find_symbol_cache(dso);
> +}
> +
> struct symbol *dso__find_symbol(struct dso *dso, u64 addr)
> {
> if (dso->last_find_result.addr != addr || dso->last_find_result.symbol == NULL) {
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index 03e264a27cd3..60345691db09 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -130,6 +130,8 @@ int dso__load_kallsyms(struct dso *dso, const char *filename, struct map *map);
>
> void dso__insert_symbol(struct dso *dso,
> struct symbol *sym);
> +void dso__delete_symbol(struct dso *dso,
> + struct symbol *sym);
>
> struct symbol *dso__find_symbol(struct dso *dso, u64 addr);
> struct symbol *dso__find_symbol_by_name(struct dso *dso, const char *name);
> --
> 2.26.2
>