[patch 2/3] perf: Use local_irq_save_nmi()

Peter Zijlstra
2010-04-06T13:39:48Z

[-- Attachment #1: perf-fix-perf_output_lock.patch --]
[-- Type: text/plain, Size: 2529 bytes --]

Patch 8bb39f9 (perf: Fix 'perf sched record' deadlock) introduced a
local_irq_save() in NMI context, convert that to local_irq_save_nmi()
and move the IRQ disable into perf_output_lock/unlock().

The former is needed because we now disallow local_irq_disable() from
NMI context due to some arch limitations.

The second is because its really about IRQ lock inversion with that
funny output lock, and perf_event_task_output() is only one site that
could trigger it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
---
include/linux/perf_event.h | 1 +
kernel/perf_event.c | 17 ++++++-----------
2 files changed, 7 insertions(+), 11 deletions(-)

Index: linux-2.6/include/linux/perf_event.h
===================================================================
--- linux-2.6.orig/include/linux/perf_event.h
+++ linux-2.6/include/linux/perf_event.h
@@ -758,6 +758,7 @@ struct perf_output_handle {
struct perf_mmap_data *data;
unsigned long head;
unsigned long offset;
+ unsigned long flags;
int nmi;
int sample;
int locked;
Index: linux-2.6/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/kernel/perf_event.c
+++ linux-2.6/kernel/perf_event.c
@@ -2848,6 +2848,10 @@ static void perf_output_lock(struct perf
struct perf_mmap_data *data = handle->data;
int cur, cpu = get_cpu();

+ /*
+ * Since this is a lock we need to be IRQ-safe
+ */
+ local_irq_save_nmi(handle->flags);
handle->locked = 0;

for (;;) {
@@ -2906,6 +2910,7 @@ again:
if (atomic_xchg(&data->wakeup, 0))
perf_output_wakeup(handle);
out:
+ local_irq_restore_nmi(handle->flags);
put_cpu();
}

@@ -3385,19 +3390,10 @@ static void perf_event_task_output(struc
unsigned long flags;
int size, ret;

- /*
- * If this CPU attempts to acquire an rq lock held by a CPU spinning
- * in perf_output_lock() from interrupt context, it's game over.
- */
- local_irq_save(flags);
-
size = task_event->event_id.header.size;
ret = perf_output_begin(&handle, event, size, 0, 0);
-
- if (ret) {
- local_irq_restore(flags);
+ if (ret)
return;
- }

task_event->event_id.pid = perf_event_pid(event, task);
task_event->event_id.ppid = perf_event_pid(event, current);
@@ -3408,7 +3404,6 @@ static void perf_event_task_output(struc
perf_output_put(&handle, task_event->event_id);

perf_output_end(&handle);
- local_irq_restore(flags);
}

static int perf_event_task_match(struct perf_event *event)