Re: [PATCH v2 1/4] powerpc/kprobes: Pause function_graph tracing during jprobes handling
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: 2017-06-08 13:44:04
On Thu, 1 Jun 2017 16:18:15 +0530 "Naveen N. Rao" [off-list ref] 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 <redacted>Acked-by: Masami Hiramatsu <mhiramat@kernel.org> Thanks!
quoted hunk ↗ jump to hunk
--- 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 [off-list ref]