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perf: Rework perf_event_exit_event() 

Make perf_event_exit_event() more robust, such that we can use it from
other contexts. Specifically the up and coming remove_on_exec.

For this to work we need to address a few issues. Remove_on_exec will
not destroy the entire context, so we cannot rely on TASK_TOMBSTONE to
disable event_function_call() and we thus have to use
perf_remove_from_context().

When using perf_remove_from_context(), there's two races to consider.
The first is against close(), where we can have concurrent tear-down
of the event. The second is against child_list iteration, which should
not find a half baked event.

To address this, teach perf_remove_from_context() to special case
!ctx->is_active and about DETACH_CHILD.

[ elver@google.com: fix racing parent/child exit in sync_child_event(). ]
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210408103605.1676875-2-elver@google.com
This commit is contained in:
Peter Zijlstra 2021-04-08 12:35:56 +02:00
parent 874fc35cdd
commit ef54c1a476
2 changed files with 83 additions and 66 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/perf_event.h
View File

@ -607,6 +607,7 @@ struct swevent_hlist {
#define PERF_ATTACH_TASK_DATA 0x08
#define PERF_ATTACH_ITRACE 0x10
#define PERF_ATTACH_SCHED_CB 0x20
#define PERF_ATTACH_CHILD 0x40
struct perf_cgroup;
struct perf_buffer;

148
kernel/events/core.c
View File

@ -2205,6 +2205,26 @@ out:
perf_event__header_size(leader);
}
static void sync_child_event(struct perf_event *child_event);
static void perf_child_detach(struct perf_event *event)
{
struct perf_event *parent_event = event->parent;
if (!(event->attach_state & PERF_ATTACH_CHILD))
return;
event->attach_state &= ~PERF_ATTACH_CHILD;
if (WARN_ON_ONCE(!parent_event))
return;
lockdep_assert_held(&parent_event->child_mutex);
sync_child_event(event);
list_del_init(&event->child_list);
}
static bool is_orphaned_event(struct perf_event *event)
{
return event->state == PERF_EVENT_STATE_DEAD;
@ -2312,6 +2332,7 @@ group_sched_out(struct perf_event *group_event,
}
#define DETACH_GROUP 0x01UL
#define DETACH_CHILD 0x02UL
/*
* Cross CPU call to remove a performance event
@ -2335,6 +2356,8 @@ __perf_remove_from_context(struct perf_event *event,
event_sched_out(event, cpuctx, ctx);
if (flags & DETACH_GROUP)
perf_group_detach(event);
if (flags & DETACH_CHILD)
perf_child_detach(event);
list_del_event(event, ctx);
if (!ctx->nr_events && ctx->is_active) {
@ -2363,25 +2386,21 @@ static void perf_remove_from_context(struct perf_event *event, unsigned long fla
lockdep_assert_held(&ctx->mutex);
event_function_call(event, __perf_remove_from_context, (void *)flags);
/*
* The above event_function_call() can NO-OP when it hits
* TASK_TOMBSTONE. In that case we must already have been detached
* from the context (by perf_event_exit_event()) but the grouping
* might still be in-tact.
* Because of perf_event_exit_task(), perf_remove_from_context() ought
* to work in the face of TASK_TOMBSTONE, unlike every other
* event_function_call() user.
*/
WARN_ON_ONCE(event->attach_state & PERF_ATTACH_CONTEXT);
if ((flags & DETACH_GROUP) &&
(event->attach_state & PERF_ATTACH_GROUP)) {
/*
* Since in that case we cannot possibly be scheduled, simply
* detach now.
*/
raw_spin_lock_irq(&ctx->lock);
perf_group_detach(event);
raw_spin_lock_irq(&ctx->lock);
if (!ctx->is_active) {
__perf_remove_from_context(event, __get_cpu_context(ctx),
ctx, (void *)flags);
raw_spin_unlock_irq(&ctx->lock);
return;
}
raw_spin_unlock_irq(&ctx->lock);
event_function_call(event, __perf_remove_from_context, (void *)flags);
}
/*
@ -12377,14 +12396,17 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu)
}
EXPORT_SYMBOL_GPL(perf_pmu_migrate_context);
static void sync_child_event(struct perf_event *child_event,
struct task_struct *child)
static void sync_child_event(struct perf_event *child_event)
{
struct perf_event *parent_event = child_event->parent;
u64 child_val;
if (child_event->attr.inherit_stat)
perf_event_read_event(child_event, child);
if (child_event->attr.inherit_stat) {
struct task_struct *task = child_event->ctx->task;
if (task && task != TASK_TOMBSTONE)
perf_event_read_event(child_event, task);
}
child_val = perf_event_count(child_event);
@ -12399,60 +12421,53 @@ static void sync_child_event(struct perf_event *child_event,
}
static void
perf_event_exit_event(struct perf_event *child_event,
struct perf_event_context *child_ctx,
struct task_struct *child)
perf_event_exit_event(struct perf_event *event, struct perf_event_context *ctx)
{
struct perf_event *parent_event = child_event->parent;
struct perf_event *parent_event = event->parent;
unsigned long detach_flags = 0;
if (parent_event) {
/*
* Do not destroy the 'original' grouping; because of the
* context switch optimization the original events could've
* ended up in a random child task.
*
* If we were to destroy the original group, all group related
* operations would cease to function properly after this
* random child dies.
*
* Do destroy all inherited groups, we don't care about those
* and being thorough is better.
*/
detach_flags = DETACH_GROUP | DETACH_CHILD;
mutex_lock(&parent_event->child_mutex);
}
perf_remove_from_context(event, detach_flags);
raw_spin_lock_irq(&ctx->lock);
if (event->state > PERF_EVENT_STATE_EXIT)
perf_event_set_state(event, PERF_EVENT_STATE_EXIT);
raw_spin_unlock_irq(&ctx->lock);
/*
* Do not destroy the 'original' grouping; because of the context
* switch optimization the original events could've ended up in a
* random child task.
*
* If we were to destroy the original group, all group related
* operations would cease to function properly after this random
* child dies.
*
* Do destroy all inherited groups, we don't care about those
* and being thorough is better.
* Child events can be freed.
*/
raw_spin_lock_irq(&child_ctx->lock);
WARN_ON_ONCE(child_ctx->is_active);
if (parent_event)
perf_group_detach(child_event);
list_del_event(child_event, child_ctx);
perf_event_set_state(child_event, PERF_EVENT_STATE_EXIT); /* is_event_hup() */
raw_spin_unlock_irq(&child_ctx->lock);
if (parent_event) {
mutex_unlock(&parent_event->child_mutex);
/*
* Kick perf_poll() for is_event_hup();
*/
perf_event_wakeup(parent_event);
free_event(event);
put_event(parent_event);
return;
}
/*
* Parent events are governed by their filedesc, retain them.
*/
if (!parent_event) {
perf_event_wakeup(child_event);
return;
}
/*
* Child events can be cleaned up.
*/
sync_child_event(child_event, child);
/*
* Remove this event from the parent's list
*/
WARN_ON_ONCE(parent_event->ctx->parent_ctx);
mutex_lock(&parent_event->child_mutex);
list_del_init(&child_event->child_list);
mutex_unlock(&parent_event->child_mutex);
/*
* Kick perf_poll() for is_event_hup().
*/
perf_event_wakeup(parent_event);
free_event(child_event);
put_event(parent_event);
perf_event_wakeup(event);
}
static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
@ -12509,7 +12524,7 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
perf_event_task(child, child_ctx, 0);
list_for_each_entry_safe(child_event, next, &child_ctx->event_list, event_entry)
perf_event_exit_event(child_event, child_ctx, child);
perf_event_exit_event(child_event, child_ctx);
mutex_unlock(&child_ctx->mutex);
@ -12769,6 +12784,7 @@ inherit_event(struct perf_event *parent_event,
*/
raw_spin_lock_irqsave(&child_ctx->lock, flags);
add_event_to_ctx(child_event, child_ctx);
child_event->attach_state |= PERF_ATTACH_CHILD;
raw_spin_unlock_irqrestore(&child_ctx->lock, flags);
/*