Hi Steven,
On 10/12/2018 19:30, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
>
> [
> 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
