[PATCH 1/6] perf: Reduce stack usage of perf_output_begin()

From: Peter Zijlstra
Date: Fri Oct 30 2020 - 11:21:50 EST

__perf_output_begin() has an on-stack struct perf_sample_data in the
unlikely case it needs to generate a LOST record. However, every call
to perf_output_begin() must already have a perf_sample_data on-stack.

Reported-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/powerpc/perf/imc-pmu.c | 2 +-
arch/s390/kernel/perf_cpum_sf.c | 2 +-
arch/x86/events/intel/ds.c | 4 ++--
include/linux/perf_event.h | 7 +++++--
kernel/events/core.c | 32 +++++++++++++++++---------------
kernel/events/ring_buffer.c | 20 +++++++++++---------
6 files changed, 37 insertions(+), 30 deletions(-)

--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -1336,7 +1336,7 @@ static void dump_trace_imc_data(struct p
/* If this is a valid record, create the sample */
struct perf_output_handle handle;

- if (perf_output_begin(&handle, event, header.size))
+ if (perf_output_begin(&handle, &data, event, header.size))
return;

perf_output_sample(&handle, &header, &data, event);
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -672,7 +672,7 @@ static void cpumsf_output_event_pid(stru
rcu_read_lock();

perf_prepare_sample(&header, data, event, regs);
- if (perf_output_begin(&handle, event, header.size))
+ if (perf_output_begin(&handle, data, event, header.size))
goto out;

/* Update the process ID (see also kernel/events/core.c) */
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -642,8 +642,8 @@ int intel_pmu_drain_bts_buffer(void)
rcu_read_lock();
perf_prepare_sample(&header, &data, event, &regs);

- if (perf_output_begin(&handle, event, header.size *
- (top - base - skip)))
+ if (perf_output_begin(&handle, &data, event,
+ header.size * (top - base - skip)))
goto unlock;

for (at = base; at < top; at++) {
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1400,11 +1400,14 @@ perf_event_addr_filters(struct perf_even
extern void perf_event_addr_filters_sync(struct perf_event *event);

extern int perf_output_begin(struct perf_output_handle *handle,
+ struct perf_sample_data *data,
struct perf_event *event, unsigned int size);
extern int perf_output_begin_forward(struct perf_output_handle *handle,
- struct perf_event *event,
- unsigned int size);
+ struct perf_sample_data *data,
+ struct perf_event *event,
+ unsigned int size);
extern int perf_output_begin_backward(struct perf_output_handle *handle,
+ struct perf_sample_data *data,
struct perf_event *event,
unsigned int size);

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7186,6 +7186,7 @@ __perf_event_output(struct perf_event *e
struct perf_sample_data *data,
struct pt_regs *regs,
int (*output_begin)(struct perf_output_handle *,
+ struct perf_sample_data *,
struct perf_event *,
unsigned int))
{
@@ -7198,7 +7199,7 @@ __perf_event_output(struct perf_event *e

perf_prepare_sample(&header, data, event, regs);

- err = output_begin(&handle, event, header.size);
+ err = output_begin(&handle, data, event, header.size);
if (err)
goto exit;

@@ -7264,7 +7265,7 @@ perf_event_read_event(struct perf_event
int ret;

perf_event_header__init_id(&read_event.header, &sample, event);
- ret = perf_output_begin(&handle, event, read_event.header.size);
+ ret = perf_output_begin(&handle, &sample, event, read_event.header.size);
if (ret)
return;

@@ -7533,7 +7534,7 @@ static void perf_event_task_output(struc

perf_event_header__init_id(&task_event->event_id.header, &sample, event);

- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, &sample, event,
task_event->event_id.header.size);
if (ret)
goto out;
@@ -7636,7 +7637,7 @@ static void perf_event_comm_output(struc
return;

perf_event_header__init_id(&comm_event->event_id.header, &sample, event);
- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, &sample, event,
comm_event->event_id.header.size);

if (ret)
@@ -7736,7 +7737,7 @@ static void perf_event_namespaces_output

perf_event_header__init_id(&namespaces_event->event_id.header,
&sample, event);
- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, &sample, event,
namespaces_event->event_id.header.size);
if (ret)
goto out;
@@ -7863,7 +7864,7 @@ static void perf_event_cgroup_output(str

perf_event_header__init_id(&cgroup_event->event_id.header,
&sample, event);
- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, &sample, event,
cgroup_event->event_id.header.size);
if (ret)
goto out;
@@ -7989,7 +7990,7 @@ static void perf_event_mmap_output(struc
}

perf_event_header__init_id(&mmap_event->event_id.header, &sample, event);
- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, &sample, event,
mmap_event->event_id.header.size);
if (ret)
goto out;
@@ -8299,7 +8300,7 @@ void perf_event_aux_event(struct perf_ev
int ret;

perf_event_header__init_id(&rec.header, &sample, event);
- ret = perf_output_begin(&handle, event, rec.header.size);
+ ret = perf_output_begin(&handle, &sample, event, rec.header.size);

if (ret)
return;
@@ -8333,7 +8334,7 @@ void perf_log_lost_samples(struct perf_e

perf_event_header__init_id(&lost_samples_event.header, &sample, event);

- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, &sample, event,
lost_samples_event.header.size);
if (ret)
return;
@@ -8388,7 +8389,7 @@ static void perf_event_switch_output(str

perf_event_header__init_id(&se->event_id.header, &sample, event);

- ret = perf_output_begin(&handle, event, se->event_id.header.size);
+ ret = perf_output_begin(&handle, &sample, event, se->event_id.header.size);
if (ret)
return;

@@ -8463,7 +8464,7 @@ static void perf_log_throttle(struct per

perf_event_header__init_id(&throttle_event.header, &sample, event);

- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, &sample, event,
throttle_event.header.size);
if (ret)
return;
@@ -8506,7 +8507,7 @@ static void perf_event_ksymbol_output(st

perf_event_header__init_id(&ksymbol_event->event_id.header,
&sample, event);
- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, &sample, event,
ksymbol_event->event_id.header.size);
if (ret)
return;
@@ -8596,7 +8597,7 @@ static void perf_event_bpf_output(struct

perf_event_header__init_id(&bpf_event->event_id.header,
&sample, event);
- ret = perf_output_begin(&handle, event,
+ ret = perf_output_begin(&handle, data, event,
bpf_event->event_id.header.size);
if (ret)
return;
@@ -8705,7 +8706,8 @@ static void perf_event_text_poke_output(

perf_event_header__init_id(&text_poke_event->event_id.header, &sample, event);

- ret = perf_output_begin(&handle, event, text_poke_event->event_id.header.size);
+ ret = perf_output_begin(&handle, &sample, event,
+ text_poke_event->event_id.header.size);
if (ret)
return;

@@ -8786,7 +8788,7 @@ static void perf_log_itrace_start(struct
rec.tid = perf_event_tid(event, current);

perf_event_header__init_id(&rec.header, &sample, event);
- ret = perf_output_begin(&handle, event, rec.header.size);
+ ret = perf_output_begin(&handle, &sample, event, rec.header.size);

if (ret)
return;
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -147,6 +147,7 @@ ring_buffer_has_space(unsigned long head

static __always_inline int
__perf_output_begin(struct perf_output_handle *handle,
+ struct perf_sample_data *data,
struct perf_event *event, unsigned int size,
bool backward)
{
@@ -237,18 +238,16 @@ __perf_output_begin(struct perf_output_h
handle->size = (1UL << page_shift) - offset;

if (unlikely(have_lost)) {
- struct perf_sample_data sample_data;
-
lost_event.header.size = sizeof(lost_event);
lost_event.header.type = PERF_RECORD_LOST;
lost_event.header.misc = 0;
lost_event.id = event->id;
lost_event.lost = local_xchg(&rb->lost, 0);

- perf_event_header__init_id(&lost_event.header,
- &sample_data, event);
+ /* XXX mostly redundant; @data is already fully initializes */
+ perf_event_header__init_id(&lost_event.header, data, event);
perf_output_put(handle, lost_event);
- perf_event__output_id_sample(event, handle, &sample_data);
+ perf_event__output_id_sample(event, handle, data);
}

return 0;
@@ -263,22 +262,25 @@ __perf_output_begin(struct perf_output_h
}

int perf_output_begin_forward(struct perf_output_handle *handle,
- struct perf_event *event, unsigned int size)
+ struct perf_sample_data *data,
+ struct perf_event *event, unsigned int size)
{
- return __perf_output_begin(handle, event, size, false);
+ return __perf_output_begin(handle, data, event, size, false);
}

int perf_output_begin_backward(struct perf_output_handle *handle,
+ struct perf_sample_data *data,
struct perf_event *event, unsigned int size)
{
- return __perf_output_begin(handle, event, size, true);
+ return __perf_output_begin(handle, data, event, size, true);
}

int perf_output_begin(struct perf_output_handle *handle,
+ struct perf_sample_data *data,
struct perf_event *event, unsigned int size)
{

- return __perf_output_begin(handle, event, size,
+ return __perf_output_begin(handle, data, event, size,
unlikely(is_write_backward(event)));
}