Re: [PATCH v2 1/4] powerpc/kprobes: Pause function_graph tracing during jprobes handling

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 8 Jun 2017 22:43:54 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> On Thu,  1 Jun 2017 16:18:15 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> 
> > This fixes a crash when function_graph and jprobes are used together.
> > This is essentially commit 237d28db036e ("ftrace/jprobes/x86: Fix
> > conflict between jprobes and function graph tracing"), but for powerpc.
> > 
> > Jprobes breaks function_graph tracing since the jprobe hook needs to use
> > jprobe_return(), which never returns back to the hook, but instead to
> > the original jprobe'd function. The solution is to momentarily pause
> > function_graph tracing before invoking the jprobe hook and re-enable it
> > when returning back to the original jprobe'd function.
> > 
> > Fixes: 6794c78243bfd ("powerpc64: port of the function graph tracer")
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>  
> 
> Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

For what it's worth...

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

> 
> Thanks!
> 
> > ---
> > v2: No changes since v1.
> > 
> >  arch/powerpc/kernel/kprobes.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> > index e1fb95385a9e..0554d6e66194 100644
> > --- a/arch/powerpc/kernel/kprobes.c
> > +++ b/arch/powerpc/kernel/kprobes.c
> > @@ -610,6 +610,15 @@ int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
> >  	regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
> >  #endif
> >  
> > +	/*
> > +	 * jprobes use jprobe_return() which skips the normal return
> > +	 * path of the function, and this messes up the accounting of the
> > +	 * function graph tracer.
> > +	 *
> > +	 * Pause function graph tracing while performing the jprobe function.
> > +	 */
> > +	pause_graph_tracing();
> > +
> >  	return 1;
> >  }
> >  NOKPROBE_SYMBOL(setjmp_pre_handler);
> > @@ -635,6 +644,8 @@ int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
> >  	 * saved regs...
> >  	 */
> >  	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
> > +	/* It's OK to start function graph tracing again */
> > +	unpause_graph_tracing();
> >  	preempt_enable_no_resched();
> >  	return 1;
> >  }
> > -- 
> > 2.12.2
> >   
> 
>