From: Steven Rostedt (VMware) <rost...@goodmis.org>
While doing some debugging, I kicked off the stacktrace trigger, to see
what was doing stacktraces in my code (it was causing a lot of noise in
my function traces).
I ran:
# trace-cmd record -p function -l save_stack_trace -l
save_stack_trace:stacktrace
And took a look at the trace, but all I found was this:
trace-cm-1326 0d..2 107.791049: kernel_stack: <stack trace>
trace-cm-1326 0d..2 107.791077: kernel_stack: <stack trace>
trace-cm-1326 0...2 107.791084: kernel_stack: <stack trace>
trace-cm-1326 0d..2 107.791091: kernel_stack: <stack trace>
trace-cm-1326 0d..2 107.791097: kernel_stack: <stack trace>
trace-cm-1326 0...2 107.791102: kernel_stack: <stack trace>
trace-cm-1326 0d..4 107.791109: kernel_stack: <stack trace>
trace-cm-1326 0d..2 107.791116: kernel_stack: <stack trace>
trace-cm-1326 0d..2 107.791120: kernel_stack: <stack trace>
trace-cm-1326 0...2 107.791125: kernel_stack: <stack trace>
trace-cm-1326 0d..2 107.791133: kernel_stack: <stack trace>
trace-cm-1326 0d..2 107.791140: kernel_stack: <stack trace>
trace-cm-1326 0...2 107.791145: kernel_stack: <stack trace>
trace-cm-1326 0d..4 107.791157: kernel_stack: <stack trace>
[...]
This was not very useful. I kicked off a bisect to see where it broke,
because it was working fine in 4.14, and this is a new regression in
the 4.15 rc cycle.
The culprit ended up being:
fc72ae40e30 "x86/unwind: Make CONFIG_UNWINDER_ORC=y the default in
kconfig for 64-bit"
As I find this to be a useful option, I don't want to revert it, so I
looked at how to make ftrace work with this new unwinder. I came up
with this solution. I'm not sure it is correct, but now my traces look
like this (and objtool check doesn't complain):
splice-t-1301 0d..1 203.199356: function: save_stack_trace
splice-t-1301 0d..2 203.199365: kernel_stack: <stack trace>
=> ___slab_alloc (ffffffff81221c5d)
=> __slab_alloc.isra.81 (ffffffff81221d08)
=> kmem_cache_alloc (ffffffff812227ce)
=> getname_flags (ffffffff8124d49a)
=> SyS_execve (ffffffff812459f2)
=> do_syscall_64 (ffffffff8100394c)
=> return_from_SYSCALL_64 (ffffffff817c2dd8)
splice-t-1301 0d..1 203.199379: function: save_stack_trace
splice-t-1301 0d..2 203.199382: kernel_stack: <stack trace>
=> ___slab_alloc (ffffffff81221c5d)
=> __slab_alloc.isra.81 (ffffffff81221d08)
=> kmem_cache_alloc (ffffffff812227ce)
=> create_object (ffffffff81237593)
=> kmem_cache_alloc (ffffffff81222795)
=> getname_flags (ffffffff8124d49a)
=> SyS_execve (ffffffff812459f2)
=> do_syscall_64 (ffffffff8100394c)
=> return_from_SYSCALL_64 (ffffffff817c2dd8)
splice-t-1301 0...1 203.199385: function: save_stack_trace
splice-t-1301 0...2 203.199387: kernel_stack: <stack trace>
=> getname_flags (ffffffff8124d49a)
=> SyS_execve (ffffffff812459f2)
=> do_syscall_64 (ffffffff8100394c)
=> return_from_SYSCALL_64 (ffffffff817c2dd8)
splice-t-1301 0d..1 203.199392: function: save_stack_trace
splice-t-1301 0d..2 203.199395: kernel_stack: <stack trace>
=> ___slab_alloc (ffffffff81221c5d)
=> __slab_alloc.isra.81 (ffffffff81221d08)
=> kmem_cache_alloc_trace (ffffffff81222568)
=> do_execveat_common.isra.34 (ffffffff81245171)
=> SyS_execve (ffffffff81245a0c)
=> do_syscall_64 (ffffffff8100394c)
=> return_from_SYSCALL_64 (ffffffff817c2dd8)
P.S. the culprit was SLAB_DEBUG that was doing the stack traces
Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
---
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 81bb565f4497..5d9eb722a04e 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -29,7 +29,6 @@ KASAN_SANITIZE_stacktrace.o := n
KASAN_SANITIZE_paravirt.o := n
OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o := y
-OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_test_nx.o := y
OBJECT_FILES_NON_STANDARD_paravirt_patch_$(BITS).o := y
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index c832291d948a..6ab3308d632a 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -4,6 +4,7 @@
*/
#include <linux/linkage.h>
+#include <asm/unwind_hints.h>
#include <asm/ptrace.h>
#include <asm/ftrace.h>
#include <asm/export.h>
@@ -148,9 +149,10 @@ EXPORT_SYMBOL(mcount)
ENTRY(function_hook)
retq
-END(function_hook)
+ENDPROC(function_hook)
ENTRY(ftrace_caller)
+ UNWIND_HINT_FUNC
/* save_mcount_regs fills in first two parameters */
save_mcount_regs
@@ -165,6 +167,7 @@ GLOBAL(ftrace_call)
call ftrace_stub
restore_mcount_regs
+ UNWIND_HINT_FUNC
/*
* The copied trampoline must call ftrace_epilogue as it
@@ -187,11 +190,13 @@ WEAK(ftrace_stub)
END(ftrace_caller)
ENTRY(ftrace_regs_caller)
+ UNWIND_HINT_FUNC
/* Save the current flags before any operations that can change them */
pushfq
/* added 8 bytes to save flags */
save_mcount_regs 8
+ UNWIND_HINT_REGS
/* save_mcount_regs fills in first two parameters */
GLOBAL(ftrace_regs_caller_op_ptr)
@@ -241,6 +246,7 @@ GLOBAL(ftrace_regs_call)
movq RBX(%rsp), %rbx
restore_mcount_regs
+ UNWIND_HINT_FUNC
/* Restore flags */
popfq
@@ -296,6 +302,7 @@ END(function_hook)
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ENTRY(ftrace_graph_caller)
+ UNWIND_HINT_FUNC
/* Saves rbp into %rdx and fills first parameter */
save_mcount_regs
@@ -311,11 +318,13 @@ ENTRY(ftrace_graph_caller)
call prepare_ftrace_return
restore_mcount_regs
+ UNWIND_HINT_FUNC
retq
END(ftrace_graph_caller)
GLOBAL(return_to_handler)
+ UNWIND_HINT_EMPTY
subq $24, %rsp
/* Save the return values */
