Messages in this thread Patch in this message | | | Date | Thu, 29 Oct 2020 16:58:03 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH 5/9] kprobes/ftrace: Add recursion protection to the ftrace callback |
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Hi Steve,
On Wed, 28 Oct 2020 07:52:49 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> > > If a ftrace callback does not supply its own recursion protection and > does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will > make a helper trampoline to do so before calling the callback instead of > just calling the callback directly.
So in that case the handlers will be called without preempt disabled?
> The default for ftrace_ops is going to assume recursion protection unless > otherwise specified.
This seems to skip entier handler if ftrace finds recursion. I would like to increment the missed counter even in that case.
[...] e.g.
> diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c > index 5264763d05be..5eb2604fdf71 100644 > --- a/arch/csky/kernel/probes/ftrace.c > +++ b/arch/csky/kernel/probes/ftrace.c > @@ -13,16 +13,21 @@ int arch_check_ftrace_location(struct kprobe *p) > void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > struct ftrace_ops *ops, struct pt_regs *regs) > { > + int bit; > bool lr_saver = false; > struct kprobe *p; > struct kprobe_ctlblk *kcb; > > - /* Preempt is disabled by ftrace */ > + bit = ftrace_test_recursion_trylock();
> + > + preempt_disable_notrace(); > p = get_kprobe((kprobe_opcode_t *)ip); > if (!p) { > p = get_kprobe((kprobe_opcode_t *)(ip - MCOUNT_INSN_SIZE)); > if (unlikely(!p) || kprobe_disabled(p)) > - return; > + goto out; > lr_saver = true; > }
if (bit < 0) { kprobes_inc_nmissed_count(p); goto out; }
> > @@ -56,6 +61,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > */ > __this_cpu_write(current_kprobe, NULL); > } > +out: > + preempt_enable_notrace();
if (bit >= 0) ftrace_test_recursion_unlock(bit);
> } > NOKPROBE_SYMBOL(kprobe_ftrace_handler); >
Or, we can also introduce a support function,
static inline void kprobes_inc_nmissed_ip(unsigned long ip) { struct kprobe *p;
preempt_disable_notrace(); p = get_kprobe((kprobe_opcode_t *)ip); if (p) kprobes_inc_nmissed_count(p); preempt_enable_notrace(); }
> diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c > index 4bab21c71055..5f7742b225a5 100644 > --- a/arch/parisc/kernel/ftrace.c > +++ b/arch/parisc/kernel/ftrace.c > @@ -208,13 +208,19 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > { > struct kprobe_ctlblk *kcb; > struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip);
(BTW, here is a bug... get_kprobe() must be called with preempt disabled.)
> + int bit; > > - if (unlikely(!p) || kprobe_disabled(p)) > + bit = ftrace_test_recursion_trylock();
if (bit < 0) { kprobes_inc_nmissed_ip(ip); > return; }
This may easier for you ?
Thank you,
> > + preempt_disable_notrace(); > + if (unlikely(!p) || kprobe_disabled(p)) > + goto out; > + > if (kprobe_running()) { > kprobes_inc_nmissed_count(p); > - return; > + goto out; > } > > __this_cpu_write(current_kprobe, p); > @@ -235,6 +241,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > } > } > __this_cpu_write(current_kprobe, NULL); > +out: > + preempt_enable_notrace(); > + ftrace_test_recursion_unlock(bit); > } > NOKPROBE_SYMBOL(kprobe_ftrace_handler); > > diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c > index 972cb28174b2..5df8d50c65ae 100644 > --- a/arch/powerpc/kernel/kprobes-ftrace.c > +++ b/arch/powerpc/kernel/kprobes-ftrace.c > @@ -18,10 +18,16 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, > { > struct kprobe *p; > struct kprobe_ctlblk *kcb; > + int bit; > > + bit = ftrace_test_recursion_trylock(); > + if (bit < 0) > + return; > + > + preempt_disable_notrace(); > p = get_kprobe((kprobe_opcode_t *)nip); > if (unlikely(!p) || kprobe_disabled(p)) > - return; > + goto out; > > kcb = get_kprobe_ctlblk(); > if (kprobe_running()) { > @@ -52,6 +58,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, > */ > __this_cpu_write(current_kprobe, NULL); > } > +out: > + preempt_enable_notrace(); > + ftrace_test_recursion_unlock(bit); > } > NOKPROBE_SYMBOL(kprobe_ftrace_handler); > > diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c > index b388e87a08bf..88466d7fb6b2 100644 > --- a/arch/s390/kernel/ftrace.c > +++ b/arch/s390/kernel/ftrace.c > @@ -202,13 +202,19 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > { > struct kprobe_ctlblk *kcb; > struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip); > + int bit; > > - if (unlikely(!p) || kprobe_disabled(p)) > + bit = ftrace_test_recursion_trylock(); > + if (bit < 0) > return; > > + preempt_disable_notrace(); > + if (unlikely(!p) || kprobe_disabled(p)) > + goto out; > + > if (kprobe_running()) { > kprobes_inc_nmissed_count(p); > - return; > + goto out; > } > > __this_cpu_write(current_kprobe, p); > @@ -228,6 +234,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > } > } > __this_cpu_write(current_kprobe, NULL); > +out: > + preempt_enable_notrace(); > + ftrace_test_recursion_unlock(bit); > } > NOKPROBE_SYMBOL(kprobe_ftrace_handler); > > diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c > index 681a4b36e9bb..a40a6cdfcca3 100644 > --- a/arch/x86/kernel/kprobes/ftrace.c > +++ b/arch/x86/kernel/kprobes/ftrace.c > @@ -18,11 +18,16 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > { > struct kprobe *p; > struct kprobe_ctlblk *kcb; > + int bit; > > - /* Preempt is disabled by ftrace */ > + bit = ftrace_test_recursion_trylock(); > + if (bit < 0) > + return; > + > + preempt_disable_notrace(); > p = get_kprobe((kprobe_opcode_t *)ip); > if (unlikely(!p) || kprobe_disabled(p)) > - return; > + goto out; > > kcb = get_kprobe_ctlblk(); > if (kprobe_running()) { > @@ -52,6 +57,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > */ > __this_cpu_write(current_kprobe, NULL); > } > +out: > + preempt_enable_notrace(); > + ftrace_test_recursion_unlock(bit); > } > NOKPROBE_SYMBOL(kprobe_ftrace_handler); > > -- > 2.28.0 > >
-- Masami Hiramatsu <mhiramat@kernel.org>
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