On 2015/06/27 15:44, He Kuang wrote: > When we add a kprobe point and record events by perf, the execution path > of all threads on each cpu will enter this point, but perf may only > record events on a particular thread or cpu at this kprobe point, a > check on call->perf_events list filters out the threads which perf is > not recording. > > Currently, bpf_prog will be entered at the beginning of > kprobe_perf_func() before the above check, which makes bpf_prog be > executed in every threads including determined not to be recorded > threads. A simple test can demonstrate this: > > 'bpf_prog_on_write.o' contains a bpf prog which outputs to trace buffer > when it is entered. Run a background thread 'another-dd' and 'dd' > simultaneously, but only record 'dd' thread by perf. The result shows > all threads trigger bpf_prog. > > $ another-dd if=/dev/zero of=test1 bs=4k count=1000000 > $ perf record -v --event bpf_prog_on_write.o -- dd if=/dev/zero of=test2 > bs=4k count=3 > $ cat /sys/kernel/debug/tracing/trace > another-dd-1007 [000] d... 120.225835: : generic_perform_write: > tgid=1007, pid=1007 > another-dd-1007 [000] d... 120.227123: : generic_perform_write: > tgid=1007, pid=1007 > [repeat many times...] > another-dd-1007 [000] d... 120.412395: : generic_perform_write: > tgid=1007, pid=1007 > another-dd-1007 [000] d... 120.412524: : generic_perform_write: > tgid=1007, pid=1007 > dd-1009 [000] d... 120.413080: : generic_perform_write: > tgid=1009, pid=1009 > dd-1009 [000] d... 120.414846: : generic_perform_write: > tgid=1009, pid=1009 > dd-1009 [000] d... 120.415013: : generic_perform_write: > tgid=1009, pid=1009 > another-dd-1007 [000] d... 120.416128: : generic_perform_write: > tgid=1007, pid=1007 > another-dd-1007 [000] d... 120.416295: : generic_perform_write: > tgid=1007, pid=1007 > > This patch moves the check on perf_events list ahead and skip running > bpf_prog on threads perf not care. > > After this patch: > > $ another-dd if=/dev/zero of=test1 bs=4k count=1000000 > $ perf record -v --event bpf_prog_on_write.o -- dd if=/dev/zero of=test2 > bs=4k count=3 > $ cat /sys/kernel/debug/tracing/trace > dd-994 [000] d... 46.386754: : generic_perform_write: tgid=994, pid=994 > dd-994 [000] d... 46.389167: : generic_perform_write: tgid=994, pid=994 > dd-994 [000] d... 46.389551: : generic_perform_write: tgid=994, pid=994
This looks nice :) Acked-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com> Thank you! > > Signed-off-by: He Kuang <heku...@huawei.com> > --- > kernel/trace/trace_kprobe.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > index d0ce590..5600df8 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -1141,13 +1141,13 @@ kprobe_perf_func(struct trace_kprobe *tk, struct > pt_regs *regs) > int size, __size, dsize; > int rctx; > > - if (prog && !trace_call_bpf(prog, regs)) > - return; > - > head = this_cpu_ptr(call->perf_events); > if (hlist_empty(head)) > return; > > + if (prog && !trace_call_bpf(prog, regs)) > + return; > + > dsize = __get_data_size(&tk->tp, regs); > __size = sizeof(*entry) + tk->tp.size + dsize; > size = ALIGN(__size + sizeof(u32), sizeof(u64)); > @@ -1176,13 +1176,13 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct > kretprobe_instance *ri, > int size, __size, dsize; > int rctx; > > - if (prog && !trace_call_bpf(prog, regs)) > - return; > - > head = this_cpu_ptr(call->perf_events); > if (hlist_empty(head)) > return; > > + if (prog && !trace_call_bpf(prog, regs)) > + return; > + > dsize = __get_data_size(&tk->tp, regs); > __size = sizeof(*entry) + tk->tp.size + dsize; > size = ALIGN(__size + sizeof(u32), sizeof(u64)); > -- Masami HIRAMATSU Linux Technology Research Center, System Productivity Research Dept. Center for Technology Innovation - Systems Engineering Hitachi, Ltd., Research & Development Group E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
