Re: 3.14-rc2 XFS backtrace because irqs_disabled.

Peter Zijlstra
2014-02-12T13:30:08Z

On Wed, Feb 12, 2014 at 07:40:36AM -0500, Steven Rostedt wrote:
> The pt_regs structure.
>
> That's what? 21 unsigned longs? 21 * 8 = 168. I think that's the
> culprit here.
>
> Peter and Frederic, is there a way not to store that on the stack?

Something like so?

---
include/trace/ftrace.h | 7 ++++---
kernel/trace/trace_event_perf.c | 5 ++++-
2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 1a8b28db3775..87ae3ef1d278 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -678,7 +678,7 @@ perf_trace_##call(void *__data, proto) \
struct ftrace_event_call *event_call = __data; \
struct ftrace_data_offsets_##call __maybe_unused __data_offsets;\
struct ftrace_raw_##call *entry; \
- struct pt_regs __regs; \
+ struct pt_regs *__regs; \
u64 __addr = 0, __count = 1; \
struct task_struct *__task = NULL; \
struct hlist_head *head; \
@@ -697,18 +697,19 @@ perf_trace_##call(void *__data, proto) \
sizeof(u64)); \
__entry_size -= sizeof(u32); \
\
- perf_fetch_caller_regs(&__regs); \
entry = perf_trace_buf_prepare(__entry_size, \
event_call->event.type, &__regs, &rctx); \
if (!entry) \
return; \
\
+ perf_fetch_caller_regs(__regs); \
+ \
tstruct \
\
{ assign; } \
\
perf_trace_buf_submit(entry, __entry_size, rctx, __addr, \
- __count, &__regs, head, __task); \
+ __count, __regs, head, __task); \
}

/*
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index e854f420e033..1885f4aac109 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -232,8 +232,10 @@ void perf_trace_del(struct perf_event *p_event, int flags)
tp_event->class->reg(tp_event, TRACE_REG_PERF_DEL, p_event);
}

+static DEFINE_PER_CPU(struct pt_regs, tp_regs[4]);
+
__kprobes void *perf_trace_buf_prepare(int size, unsigned short type,
- struct pt_regs *regs, int *rctxp)
+ struct pt_regs **regs, int *rctxp)
{
struct trace_entry *entry;
unsigned long flags;
@@ -252,6 +254,7 @@ __kprobes void *perf_trace_buf_prepare(int size, unsigned short type,
if (*rctxp < 0)
return NULL;

+ *regs = this_cpu_ptr(&tp_regs[*rctxp]);
raw_data = this_cpu_ptr(perf_trace_buf[*rctxp]);

/* zero the dead bytes from align to not leak stack to user */