On Tue, Mar 21, 2017 at 09:44:03PM +0100, Paul Menzel wrote:
> I checked out Linux 4.9.16, applied your patch on top, and copied the Debian
> 4.9 Linux kernel configuration, did `make menuconfig`, disabled building
> debugging symbols, and executed `ARCH=i386 make -j40 deb-pkg`.
>
> I installed that package on the Lenovo X60, and the result with tracing
> enabled has improved. The system suspends without a crash. Unfortunately,
> instead of resuming when pressing the power button, it starts from scratch.
> Suspend and resume without tracing enabled works though.
>
> I’ll try to collect logs, but I don’t know, if there will be any, if the
> system just resets.
>
> Maybe, this can be reproduced in QEMU?
So I was able to recreate this issue in qemu, and after some hours of
debugging I managed to figure it out.
It's rebooting during the resume because of a triple fault in
prepare_ftrace_return().
acpi wakeup for secondary cpu
startup_32_smp()
load_ucode_ap()
prepare_ftrace_return()
ftrace_graph_is_dead()
dereferences virtual address (kill_ftrace_graph) in real mode <-- BOOM
I tried fixing it by changing load_ucode_ap() to notrace, but that
function calls some other functions which also have mcount hooks, which
call other functions, etc.
Instead I was able to "fix" it by ignoring ftrace calls in real mode:
-----
index 8f3d9cf..5c0d0c6 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -983,6 +983,9 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
unsigned long return_hooker = (unsigned long)
&return_to_handler;
+ if (__builtin_return_address(0) < TASK_SIZE_MAX)
+ return;
+
if (unlikely(ftrace_graph_is_dead()))
return;
---------------
I'm not sure what the best fix should really be. A few ideas off the
top of my head:
- A real mode check similar to the above (except it should probably be
more precise)
- Make tracing_graph_pause a percpu variable so that it can be read from
prepare_ftrace_return()
- pause_graph_tracing() from ftrace_suspend_notifier_call()
Steven, thoughts?
--
Josh
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