[PATCH 6/6] arm64: Use ftrace_graph_get_ret_stack() instead of curr_ret_stack

[PATCH 6/6] arm64: Use ftrace_graph_get_ret_stack() instead of curr_ret_stack

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

[
  Folks, I'm working on rewriting the function graph tracer. In order to
  do so, some changes need to be done that affect architecture specific
  code. I'm only able to compile test these changes. I would like to
  have folks check out my repo and give them a test.

    git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
  ftrace/core

  Head SHA1: 51584396cff54aaf57ed0bd353767d71429f77b4
]

The structure of the ret_stack array on the task struct is going to
change, and accessing it directly via the curr_ret_stack index will no
longer give the ret_stack entry that holds the return address. To access
that, architectures must now use ftrace_graph_get_ret_stack() to get the
associated ret_stack that matches the saved return address.

Cc: linux-arm-kernel@lists.infradead.org
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/arm64/kernel/perf_callchain.c |  2 +-
 arch/arm64/kernel/process.c        |  2 +-
 arch/arm64/kernel/return_address.c |  2 +-
 arch/arm64/kernel/stacktrace.c     | 12 +++++++-----
 arch/arm64/kernel/time.c           |  2 +-
 arch/arm64/kernel/traps.c          |  2 +-
 6 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index bcafd7dcfe8b..1b792b46604e 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -164,7 +164,7 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
 	frame.fp = regs->regs[29];
 	frame.pc = regs->pc;
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	frame.graph = current->curr_ret_stack;
+	frame.graph = 0;
 #endif
 
 	walk_stackframe(current, &frame, callchain_trace, entry);
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index d9a4c2d6dd8b..37a66394b07d 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -459,7 +459,7 @@ unsigned long get_wchan(struct task_struct *p)
 	frame.fp = thread_saved_fp(p);
 	frame.pc = thread_saved_pc(p);
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	frame.graph = p->curr_ret_stack;
+	frame.graph = 0;
 #endif
 	do {
 		if (unwind_frame(p, &frame))
diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c
index 933adbc0f654..53c40196b607 100644
--- a/arch/arm64/kernel/return_address.c
+++ b/arch/arm64/kernel/return_address.c
@@ -44,7 +44,7 @@ void *return_address(unsigned int level)
 	frame.fp = (unsigned long)__builtin_frame_address(0);
 	frame.pc = (unsigned long)return_address; /* dummy */
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	frame.graph = current->curr_ret_stack;
+	frame.graph = 0;
 #endif
 
 	walk_stackframe(current, &frame, save_return_addr, &data);
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 7723dadf25be..1a29f2695ff2 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -59,15 +59,17 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	if (tsk->ret_stack &&
 			(frame->pc == (unsigned long)return_to_handler)) {
-		if (WARN_ON_ONCE(frame->graph == -1))
-			return -EINVAL;
+		struct ftrace_ret_stack *ret_stack;
 		/*
 		 * This is a case where function graph tracer has
 		 * modified a return address (LR) in a stack frame
 		 * to hook a function return.
 		 * So replace it to an original value.
 		 */
-		frame->pc = tsk->ret_stack[frame->graph--].ret;
+		ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
+		if (WARN_ON_ONCE(!ret_stack))
+			return -EINVAL;
+		frame->pc = ret_stack->ret;
 	}
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
@@ -134,7 +136,7 @@ void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 	frame.fp = regs->regs[29];
 	frame.pc = regs->pc;
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	frame.graph = current->curr_ret_stack;
+	frame.graph = 0;
 #endif
 
 	walk_stackframe(current, &frame, save_trace, &data);
@@ -165,7 +167,7 @@ static noinline void __save_stack_trace(struct task_struct *tsk,
 		frame.pc = (unsigned long)__save_stack_trace;
 	}
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	frame.graph = tsk->curr_ret_stack;
+	frame.graph = 0;
 #endif
 
 	walk_stackframe(tsk, &frame, save_trace, &data);
diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c
index f258636273c9..a777ae90044d 100644
--- a/arch/arm64/kernel/time.c
+++ b/arch/arm64/kernel/time.c
@@ -52,7 +52,7 @@ unsigned long profile_pc(struct pt_regs *regs)
 	frame.fp = regs->regs[29];
 	frame.pc = regs->pc;
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	frame.graph = current->curr_ret_stack;
+	frame.graph = 0;
 #endif
 	do {
 		int ret = unwind_frame(NULL, &frame);
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 5f4d9acb32f5..49ebf3771391 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -122,7 +122,7 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 		frame.pc = thread_saved_pc(tsk);
 	}
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	frame.graph = tsk->curr_ret_stack;
+	frame.graph = 0;
 #endif
 
 	skip = !!regs;
-- 
2.19.1



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Re: [PATCH 6/6] arm64: Use ftrace_graph_get_ret_stack() instead of curr_ret_stack

[James Morse]

Hi Steven,

On 10/12/2018 19:30, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> 
> [
>   Folks, I'm working on rewriting the function graph tracer. In order to
>   do so, some changes need to be done that affect architecture specific
>   code. I'm only able to compile test these changes. I would like to
>   have folks check out my repo and give them a test.
> 
>     git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
>   ftrace/core
> 
>   Head SHA1: 51584396cff54aaf57ed0bd353767d71429f77b4
> ]
> 
> The structure of the ret_stack array on the task struct is going to
> change, and accessing it directly via the curr_ret_stack index will no
> longer give the ret_stack entry that holds the return address. To access
> that, architectures must now use ftrace_graph_get_ret_stack() to get the
> associated ret_stack that matches the saved return address.

I gave this branch a spin, but I hit the WARN_ON() fairly easily:

root@debian-guest:~# echo function_graph > /sys/kernel/debug/tracing/current_tracer
root@debian-guest:~# ps
[   27.744824] WARNING: CPU: 0 PID: 2457 at arch/arm64/kernel/stacktrace.c:70
unwind_frame+0x78/0x128
[   27.745174] Modules linked in:
[   27.745375] CPU: 0 PID: 2457 Comm: ps Not tainted
4.20.0-rc3-00038-g51584396cff5 #10814
[   27.745697] Hardware name: linux,dummy-virt (DT)
[   27.745918] pstate: 80400005 (Nzcv daif +PAN -UAO)
[   27.746151] pc : unwind_frame+0x78/0x128
[   27.746337] lr : unwind_frame+0x114/0x128
[   27.746511] sp : ffff00000c893a80
[   27.746685] x29: ffff00000c893a80 x28: 0000000000000000
[   27.746914] x27: ffffffffffffffff x26: 0000000000000001
[   27.747150] x25: 0000000000000049 x24: ffff000009662940
[   27.747375] x23: 0000000000000001 x22: ffff0000096496c8
[   27.747622] x21: ffff0000096496c8 x20: 000000000000000f
[   27.747851] x19: ffff00000c893ad0 x18: 0000000000000000
[   27.748078] x17: 0000000000000000 x16: 0000000000000000
[   27.748337] x15: 0000000000000000 x14: 0000000000000000
[   27.748563] x13: ffff80000a6b2500 x12: 0000000000300000
[   27.748790] x11: 0000000000281bad x10: 0000000000000528
[   27.749322] x9 : ffff80000c808400 x8 : 0000000000000030
[   27.749557] x7 : ffff80000a503520 x6 : 0000000000000528
[   27.749790] x5 : 0000000000019a3b x4 : ffff80000a6b2580
[   27.750010] x3 : ffff80000c1a0d80 x2 : 0000000000000001
[   27.750236] x1 : 000000000000000a x0 : 0000000000000000
[   27.750460] Call trace:
[   27.750587]  unwind_frame+0x78/0x128
[   27.750761]  get_wchan+0xa4/0x110
[   27.750926]  do_task_stat+0x8d4/0x9e8
[   27.751097]  proc_tgid_stat+0x40/0x50
[   27.751271]  proc_single_show+0x5c/0xb8
[   27.751448]  seq_read+0x138/0x450
[   27.751614]  __vfs_read+0x60/0x170
[   27.751782]  vfs_read+0x94/0x150
[   27.751948]  ksys_read+0x6c/0xd0
[   27.752129]  __arm64_sys_read+0x24/0x30
[   27.752309]  el0_svc_common+0x94/0xe8
[   27.752479]  el0_svc_handler+0x38/0x78
[   27.752642]  el0_svc+0x8/0xc
[   27.752804] ---[ end trace fdae6e80cafbfff9 ]---
  PID TTY          TIME CMD
 2401 hvc0     00:00:00 login
 2451 hvc0     00:00:00 bash
 2457 hvc0     00:00:00 ps

This is single cpu kvm guest, with arm64's defconfig and:
| CONFIG_GENERIC_TRACER=y
| CONFIG_FUNCTION_TRACER=y
| CONFIG_FUNCTION_GRAPH_TRACER=y

This doesn't happen with the same configuration on v4.20-rc4.


> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 7723dadf25be..1a29f2695ff2 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -59,15 +59,17 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  	if (tsk->ret_stack &&
>  			(frame->pc == (unsigned long)return_to_handler)) {
> -		if (WARN_ON_ONCE(frame->graph == -1))
> -			return -EINVAL;
> +		struct ftrace_ret_stack *ret_stack;
>  		/*
>  		 * This is a case where function graph tracer has
>  		 * modified a return address (LR) in a stack frame
>  		 * to hook a function return.
>  		 * So replace it to an original value.
>  		 */
> -		frame->pc = tsk->ret_stack[frame->graph--].ret;
> +		ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
> +		if (WARN_ON_ONCE(!ret_stack))
> +			return -EINVAL;
> +		frame->pc = ret_stack->ret;
>  	}
>  #endif /* CONFIG_FUNCTION_GRAPH_TRACER */


Thanks,

James

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Re: [PATCH 6/6] arm64: Use ftrace_graph_get_ret_stack() instead of curr_ret_stack

[Steven Rostedt]

On Thu, 13 Dec 2018 17:09:35 +0000
James Morse <james.morse@arm.com> wrote:

> Hi Steven,
> 

> I gave this branch a spin, but I hit the WARN_ON() fairly easily:

Thanks for testing!

Can you see if this patch fixes it for you?

-- Steve

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index d4f04f0ca646..8dfd5021b933 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -246,10 +246,10 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
 struct ftrace_ret_stack *
 ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
 {
-	idx = current->curr_ret_stack - idx;
+	idx = task->curr_ret_stack - idx;
 
 	if (idx >= 0 && idx <= task->curr_ret_stack)
-		return &current->ret_stack[idx];
+		return &task->ret_stack[idx];
 
 	return NULL;
 }


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Re: [PATCH 6/6] arm64: Use ftrace_graph_get_ret_stack() instead of curr_ret_stack

[James Morse]

Hi Steve,

On 15/12/2018 03:00, Steven Rostedt wrote:
> On Thu, 13 Dec 2018 17:09:35 +0000
> James Morse <james.morse@arm.com> wrote:
>> I gave this branch a spin, but I hit the WARN_ON() fairly easily:
> 
> Thanks for testing!
> 
> Can you see if this patch fixes it for you?

> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index d4f04f0ca646..8dfd5021b933 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -246,10 +246,10 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
>  struct ftrace_ret_stack *
>  ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
>  {
> -	idx = current->curr_ret_stack - idx;
> +	idx = task->curr_ret_stack - idx;
>  
>  	if (idx >= 0 && idx <= task->curr_ret_stack)
> -		return &current->ret_stack[idx];
> +		return &task->ret_stack[idx];
>  
>  	return NULL;
>  }
> 

Heh, yes that fixes it:

Tested-by: James Morse <james.morse@arm.com>


Thanks,

James

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