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Message-ID: <20171227020046.tcsorhzsxvp5awcg@ast-mbp> Date: Tue, 26 Dec 2017 18:00:47 -0800 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Masami Hiramatsu <mhiramat@...nel.org> Cc: Alexei Starovoitov <ast@...com>, Josef Bacik <jbacik@...com>, rostedt@...dmis.org, mingo@...hat.com, davem@...emloft.net, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, ast@...nel.org, kernel-team@...com, daniel@...earbox.net, linux-btrfs@...r.kernel.org, darrick.wong@...cle.com, Josef Bacik <josef@...icpanda.com>, Akinobu Mita <akinobu.mita@...il.com> Subject: Re: [RFC PATCH bpf-next v2 2/4] tracing/kprobe: bpf: Compare instruction pointer with original one On Tue, Dec 26, 2017 at 04:47:26PM +0900, Masami Hiramatsu wrote: > Compare instruction pointer with original one on the > stack instead using per-cpu bpf_kprobe_override flag. > > This patch also consolidates reset_current_kprobe() and > preempt_enable_no_resched() blocks. Those can be done > in one place. > > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org> > --- > kernel/trace/bpf_trace.c | 1 - > kernel/trace/trace_kprobe.c | 21 +++++++-------------- > 2 files changed, 7 insertions(+), 15 deletions(-) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index d663660f8392..cefa9b0e396c 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -83,7 +83,6 @@ EXPORT_SYMBOL_GPL(trace_call_bpf); > #ifdef CONFIG_BPF_KPROBE_OVERRIDE > BPF_CALL_2(bpf_override_return, struct pt_regs *, regs, unsigned long, rc) > { > - __this_cpu_write(bpf_kprobe_override, 1); > regs_set_return_value(regs, rc); > arch_ftrace_kprobe_override_function(regs); > return 0; > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > index 265e3e27e8dc..a7c7035963f2 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -42,8 +42,6 @@ struct trace_kprobe { > (offsetof(struct trace_kprobe, tp.args) + \ > (sizeof(struct probe_arg) * (n))) > > -DEFINE_PER_CPU(int, bpf_kprobe_override); > - > static nokprobe_inline bool trace_kprobe_is_return(struct trace_kprobe *tk) > { > return tk->rp.handler != NULL; > @@ -1204,6 +1202,7 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs) > int rctx; > > if (bpf_prog_array_valid(call)) { > + unsigned long orig_ip = instruction_pointer(regs); > int ret; > > ret = trace_call_bpf(call, regs); > @@ -1211,12 +1210,13 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs) > /* > * We need to check and see if we modified the pc of the > * pt_regs, and if so clear the kprobe and return 1 so that we > - * don't do the instruction skipping. Also reset our state so > - * we are clean the next pass through. > + * don't do the single stepping. > + * The ftrace kprobe handler leaves it up to us to re-enable > + * preemption here before returning if we've modified the ip. > */ > - if (__this_cpu_read(bpf_kprobe_override)) { > - __this_cpu_write(bpf_kprobe_override, 0); > + if (orig_ip != instruction_pointer(regs)) { > reset_current_kprobe(); > + preempt_enable_no_resched(); This is great idea. Acked-by: Alexei Starovoitov <ast@...nel.org>
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