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perf/core: Simplify the perf_event_alloc() error path
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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>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lore.kernel.org/r/20241104135517.967889521@infradead.org
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Peter Zijlstra authored and Ingo Molnar committed Mar 4, 2025
1 parent 061c991 commit c70ca29
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Showing 2 changed files with 78 additions and 76 deletions.
16 changes: 9 additions & 7 deletions include/linux/perf_event.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -673,13 +673,15 @@ struct swevent_hlist {
struct rcu_head rcu_head;
};

#define PERF_ATTACH_CONTEXT 0x01
#define PERF_ATTACH_GROUP 0x02
#define PERF_ATTACH_TASK 0x04
#define PERF_ATTACH_TASK_DATA 0x08
#define PERF_ATTACH_ITRACE 0x10
#define PERF_ATTACH_SCHED_CB 0x20
#define PERF_ATTACH_CHILD 0x40
#define PERF_ATTACH_CONTEXT 0x0001
#define PERF_ATTACH_GROUP 0x0002
#define PERF_ATTACH_TASK 0x0004
#define PERF_ATTACH_TASK_DATA 0x0008
#define PERF_ATTACH_ITRACE 0x0010
#define PERF_ATTACH_SCHED_CB 0x0020
#define PERF_ATTACH_CHILD 0x0040
#define PERF_ATTACH_EXCLUSIVE 0x0080
#define PERF_ATTACH_CALLCHAIN 0x0100

struct bpf_prog;
struct perf_cgroup;
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138 changes: 69 additions & 69 deletions kernel/events/core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5289,21 +5289,22 @@ static int exclusive_event_init(struct perf_event *event)
return -EBUSY;
}

event->attach_state |= PERF_ATTACH_EXCLUSIVE;

return 0;
}

static void exclusive_event_destroy(struct perf_event *event)
{
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)
Expand Down Expand Up @@ -5362,40 +5363,20 @@ static void perf_pending_task_sync(struct perf_event *event)
rcuwait_wait_event(&event->pending_work_wait, !event->pending_work, TASK_UNINTERRUPTIBLE);
}

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);
irq_work_sync(&event->pending_disable_irq);
perf_pending_task_sync(event);
if (event->attach_state & PERF_ATTACH_CALLCHAIN)
put_callchain_buffers();

unaccount_event(event);
kfree(event->addr_filter_ranges);

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 (event->attach_state & PERF_ATTACH_EXCLUSIVE)
exclusive_event_destroy(event);

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->destroy)
event->destroy(event);

Expand All @@ -5406,22 +5387,58 @@ static void _free_event(struct perf_event *event)
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);
irq_work_sync(&event->pending_disable_irq);
perf_pending_task_sync(event);

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.
Expand Down Expand Up @@ -12093,8 +12110,10 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
event->destroy(event);
}

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

return ret;
}
Expand Down Expand Up @@ -12422,15 +12441,15 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
* See perf_output_read().
*/
if (has_inherit_and_sample_read(attr) && !(attr->sample_type & PERF_SAMPLE_TID))
goto err_ns;
goto err;

if (!has_branch_stack(event))
event->attr.branch_sample_type = 0;

pmu = perf_init_event(event);
if (IS_ERR(pmu)) {
err = PTR_ERR(pmu);
goto err_ns;
goto err;
}

/*
Expand All @@ -12440,46 +12459,46 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
*/
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) ||
event->attr.aux_pause || event->attr.aux_resume)) {
err = -EOPNOTSUPP;
goto err_pmu;
goto err;
}

if (event->attr.aux_pause && event->attr.aux_resume) {
err = -EINVAL;
goto err_pmu;
goto err;
}

if (event->attr.aux_start_paused) {
if (!(pmu->capabilities & PERF_PMU_CAP_AUX_PAUSE)) {
err = -EOPNOTSUPP;
goto err_pmu;
goto err;
}
event->hw.aux_paused = 1;
}

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,
sizeof(struct perf_addr_filter_range),
GFP_KERNEL);
if (!event->addr_filter_ranges) {
err = -ENOMEM;
goto err_per_task;
goto err;
}

/*
Expand All @@ -12504,41 +12523,22 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) {
err = get_callchain_buffers(attr->sample_max_stack);
if (err)
goto err_addr_filters;
goto err;
event->attach_state |= PERF_ATTACH_CALLCHAIN;
}
}

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);
}

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