[PATCH 01/13] perf: Simplify perf_event_alloc() error path

Peter Zijlstra
2023-11-02T15:33:24Z

The error cleanup sequence in perf_event_alloc() is a subset of the
existing _free_event() function (it must of course be).

Split this out into __free_event() and simplify the error path.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/perf_event.h | 1
kernel/events/core.c | 129 ++++++++++++++++++++++-----------------------
2 files changed, 66 insertions(+), 64 deletions(-)

--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -634,6 +634,7 @@ struct swevent_hlist {
#define PERF_ATTACH_ITRACE 0x10
#define PERF_ATTACH_SCHED_CB 0x20
#define PERF_ATTACH_CHILD 0x40
+#define PERF_ATTACH_EXCLUSIVE 0x80

struct bpf_prog;
struct perf_cgroup;
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5094,6 +5094,8 @@ static int exclusive_event_init(struct p
return -EBUSY;
}

+ event->attach_state |= PERF_ATTACH_EXCLUSIVE;
+
return 0;
}

@@ -5101,14 +5103,13 @@ static void exclusive_event_destroy(stru
{
struct pmu *pmu = event->pmu;

- if (!is_exclusive_pmu(pmu))
- return;
-
/* see comment in exclusive_event_init() */
if (event->attach_state & PERF_ATTACH_TASK)
atomic_dec(&pmu->exclusive_cnt);
else
atomic_inc(&pmu->exclusive_cnt);
+
+ event->attach_state &= ~PERF_ATTACH_EXCLUSIVE;
}

static bool exclusive_event_match(struct perf_event *e1, struct perf_event *e2)
@@ -5143,38 +5144,22 @@ static bool exclusive_event_installable(
static void perf_addr_filters_splice(struct perf_event *event,
struct list_head *head);

-static void _free_event(struct perf_event *event)
+/* vs perf_event_alloc() error */
+static void __free_event(struct perf_event *event)
{
- irq_work_sync(&event->pending_irq);
-
- unaccount_event(event);
-
- security_perf_event_free(event);
-
- if (event->rb) {
- /*
- * Can happen when we close an event with re-directed output.
- *
- * Since we have a 0 refcount, perf_mmap_close() will skip
- * over us; possibly making our ring_buffer_put() the last.
- */
- mutex_lock(&event->mmap_mutex);
- ring_buffer_attach(event, NULL);
- mutex_unlock(&event->mmap_mutex);
- }
-
- if (is_cgroup_event(event))
- perf_detach_cgroup(event);
-
if (!event->parent) {
if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
put_callchain_buffers();
}

- perf_event_free_bpf_prog(event);
- perf_addr_filters_splice(event, NULL);
kfree(event->addr_filter_ranges);

+ if (event->attach_state & PERF_ATTACH_EXCLUSIVE)
+ exclusive_event_destroy(event);
+
+ if (is_cgroup_event(event))
+ perf_detach_cgroup(event);
+
if (event->destroy)
event->destroy(event);

@@ -5185,22 +5170,56 @@ static void _free_event(struct perf_even
if (event->hw.target)
put_task_struct(event->hw.target);

- if (event->pmu_ctx)
+ if (event->pmu_ctx) {
+ /*
+ * put_pmu_ctx() needs an event->ctx reference, because of
+ * epc->ctx.
+ */
+ WARN_ON_ONCE(!event->ctx);
+ WARN_ON_ONCE(event->pmu_ctx->ctx != event->ctx);
put_pmu_ctx(event->pmu_ctx);
+ }

/*
- * perf_event_free_task() relies on put_ctx() being 'last', in particular
- * all task references must be cleaned up.
+ * perf_event_free_task() relies on put_ctx() being 'last', in
+ * particular all task references must be cleaned up.
*/
if (event->ctx)
put_ctx(event->ctx);

- exclusive_event_destroy(event);
- module_put(event->pmu->module);
+ if (event->pmu)
+ module_put(event->pmu->module);

call_rcu(&event->rcu_head, free_event_rcu);
}

+/* vs perf_event_alloc() success */
+static void _free_event(struct perf_event *event)
+{
+ irq_work_sync(&event->pending_irq);
+
+ unaccount_event(event);
+
+ security_perf_event_free(event);
+
+ if (event->rb) {
+ /*
+ * Can happen when we close an event with re-directed output.
+ *
+ * Since we have a 0 refcount, perf_mmap_close() will skip
+ * over us; possibly making our ring_buffer_put() the last.
+ */
+ mutex_lock(&event->mmap_mutex);
+ ring_buffer_attach(event, NULL);
+ mutex_unlock(&event->mmap_mutex);
+ }
+
+ perf_event_free_bpf_prog(event);
+ perf_addr_filters_splice(event, NULL);
+
+ __free_event(event);
+}
+
/*
* Used to free events which have a known refcount of 1, such as in error paths
* where the event isn't exposed yet and inherited events.
@@ -11591,8 +11610,10 @@ static int perf_try_init_event(struct pm
event->destroy(event);
}

- if (ret)
+ if (ret) {
+ event->pmu = NULL;
module_put(pmu->module);
+ }

return ret;
}
@@ -11918,7 +11939,7 @@ perf_event_alloc(struct perf_event_attr
* See perf_output_read().
*/
if (attr->inherit && (attr->sample_type & PERF_SAMPLE_READ))
- goto err_ns;
+ goto err;

if (!has_branch_stack(event))
event->attr.branch_sample_type = 0;
@@ -11926,7 +11947,7 @@ perf_event_alloc(struct perf_event_attr
pmu = perf_init_event(event);
if (IS_ERR(pmu)) {
err = PTR_ERR(pmu);
- goto err_ns;
+ goto err;
}

/*
@@ -11936,24 +11957,24 @@ perf_event_alloc(struct perf_event_attr
*/
if (pmu->task_ctx_nr == perf_invalid_context && (task || cgroup_fd != -1)) {
err = -EINVAL;
- goto err_pmu;
+ goto err;
}

if (event->attr.aux_output &&
!(pmu->capabilities & PERF_PMU_CAP_AUX_OUTPUT)) {
err = -EOPNOTSUPP;
- goto err_pmu;
+ goto err;
}

if (cgroup_fd != -1) {
err = perf_cgroup_connect(cgroup_fd, event, attr, group_leader);
if (err)
- goto err_pmu;
+ goto err;
}

err = exclusive_event_init(event);
if (err)
- goto err_pmu;
+ goto err;

if (has_addr_filter(event)) {
event->addr_filter_ranges = kcalloc(pmu->nr_addr_filters,
@@ -11961,7 +11982,7 @@ perf_event_alloc(struct perf_event_attr
GFP_KERNEL);
if (!event->addr_filter_ranges) {
err = -ENOMEM;
- goto err_per_task;
+ goto err;
}

/*
@@ -11986,41 +12007,21 @@ perf_event_alloc(struct perf_event_attr
if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) {
err = get_callchain_buffers(attr->sample_max_stack);
if (err)
- goto err_addr_filters;
+ goto err;
}
}

err = security_perf_event_alloc(event);
if (err)
- goto err_callchain_buffer;
+ goto err;

/* symmetric to unaccount_event() in _free_event() */
account_event(event);

return event;

-err_callchain_buffer:
- if (!event->parent) {
- if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)
- put_callchain_buffers();
- }
-err_addr_filters:
- kfree(event->addr_filter_ranges);
-
-err_per_task:
- exclusive_event_destroy(event);
-
-err_pmu:
- if (is_cgroup_event(event))
- perf_detach_cgroup(event);
- if (event->destroy)
- event->destroy(event);
- module_put(pmu->module);
-err_ns:
- if (event->hw.target)
- put_task_struct(event->hw.target);
- call_rcu(&event->rcu_head, free_event_rcu);
-
+err:
+ __free_event(event);
return ERR_PTR(err);
}