From 79fdee9b6355c9720f14717e1ad66af51bb331b5 Mon Sep 17 00:00:00 2001 From: AKASHI Takahiro Date: Tue, 15 Dec 2015 17:33:39 +0900 Subject: [PATCH] arm64: ftrace: modify a stack frame in a safe way Function graph tracer modifies a return address (LR) in a stack frame by calling ftrace_prepare_return() in a traced function's function prologue. The current code does this modification before preserving an original address at ftrace_push_return_trace() and there is always a small window of inconsistency when an interrupt occurs. This doesn't matter, as far as an interrupt stack is introduced, because stack tracer won't be invoked in an interrupt context. But it would be better to proactively minimize such a window by moving the LR modification after ftrace_push_return_trace(). Signed-off-by: AKASHI Takahiro Signed-off-by: Will Deacon --- arch/arm64/kernel/ftrace.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index 8f7005bc35bd..ebecf9aa33d1 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -129,23 +129,20 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, * on other archs. It's unlikely on AArch64. */ old = *parent; - *parent = return_hooker; trace.func = self_addr; trace.depth = current->curr_ret_stack + 1; /* Only trace if the calling function expects to */ - if (!ftrace_graph_entry(&trace)) { - *parent = old; + if (!ftrace_graph_entry(&trace)) return; - } err = ftrace_push_return_trace(old, self_addr, &trace.depth, frame_pointer); - if (err == -EBUSY) { - *parent = old; + if (err == -EBUSY) return; - } + else + *parent = return_hooker; } #ifdef CONFIG_DYNAMIC_FTRACE -- 2.20.1