On Thu, 1 Jun 2017 16:18:15 +0530
"Naveen N. Rao" <naveen.n....@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....@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhira...@kernel.org>
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
>
--
Masami Hiramatsu <mhira...@kernel.org>
