[PATCH v2 1/7] perf: propagate perf_install_in_context errors up

[Ian Rogers]

The current __perf_install_in_context can fail and the error is ignored.
Changing __perf_install_in_context can add new failure modes that need
errors propagating up. This change prepares for this.

Signed-off-by: Ian Rogers <irog...@google.com>
---
 kernel/events/core.c | 39 ++++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index eea9d52b010c..84a22a5c88b0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2561,11 +2561,12 @@ static bool exclusive_event_installable(struct 
perf_event *event,
  *
  * Very similar to event_function_call, see comment there.
  */
-static void
+static int
 perf_install_in_context(struct perf_event_context *ctx,
                        struct perf_event *event,
                        int cpu)
 {
+       int err;
        struct task_struct *task = READ_ONCE(ctx->task);
 
        lockdep_assert_held(&ctx->mutex);
@@ -2582,15 +2583,15 @@ perf_install_in_context(struct perf_event_context *ctx,
        smp_store_release(&event->ctx, ctx);
 
        if (!task) {
-               cpu_function_call(cpu, __perf_install_in_context, event);
-               return;
+               err = cpu_function_call(cpu, __perf_install_in_context, event);
+               return err;
        }
 
        /*
         * Should not happen, we validate the ctx is still alive before calling.
         */
        if (WARN_ON_ONCE(task == TASK_TOMBSTONE))
-               return;
+               return 0;
 
        /*
         * Installing events is tricky because we cannot rely on ctx->is_active
@@ -2624,9 +2625,11 @@ perf_install_in_context(struct perf_event_context *ctx,
         */
        smp_mb();
 again:
-       if (!task_function_call(task, __perf_install_in_context, event))
-               return;
+       err = task_function_call(task, __perf_install_in_context, event);
+       if (!err)
+               return 0;
 
+       WARN_ON_ONCE(err != -ESRCH);
        raw_spin_lock_irq(&ctx->lock);
        task = ctx->task;
        if (WARN_ON_ONCE(task == TASK_TOMBSTONE)) {
@@ -2636,7 +2639,7 @@ perf_install_in_context(struct perf_event_context *ctx,
                 * against perf_event_exit_task_context().
                 */
                raw_spin_unlock_irq(&ctx->lock);
-               return;
+               return 0;
        }
        /*
         * If the task is not running, ctx->lock will avoid it becoming so,
@@ -2648,6 +2651,7 @@ perf_install_in_context(struct perf_event_context *ctx,
        }
        add_event_to_ctx(event, ctx);
        raw_spin_unlock_irq(&ctx->lock);
+       return 0;
 }
 
 /*
@@ -11130,7 +11134,9 @@ SYSCALL_DEFINE5(perf_event_open,
                 */
                for_each_sibling_event(sibling, group_leader) {
                        perf_event__state_init(sibling);
-                       perf_install_in_context(ctx, sibling, sibling->cpu);
+                       err = perf_install_in_context(ctx, sibling,
+                                                     sibling->cpu);
+                       WARN_ON_ONCE(err);
                        get_ctx(ctx);
                }
 
@@ -11140,7 +11146,9 @@ SYSCALL_DEFINE5(perf_event_open,
                 * startup state, ready to be add into new context.
                 */
                perf_event__state_init(group_leader);
-               perf_install_in_context(ctx, group_leader, group_leader->cpu);
+               err = perf_install_in_context(ctx, group_leader,
+                                             group_leader->cpu);
+               WARN_ON_ONCE(err);
                get_ctx(ctx);
        }
 
@@ -11155,7 +11163,8 @@ SYSCALL_DEFINE5(perf_event_open,
 
        event->owner = current;
 
-       perf_install_in_context(ctx, event, event->cpu);
+       err = perf_install_in_context(ctx, event, event->cpu);
+       WARN_ON_ONCE(err);
        perf_unpin_context(ctx);
 
        if (move_group)
@@ -11274,7 +11283,8 @@ perf_event_create_kernel_counter(struct perf_event_attr 
*attr, int cpu,
                goto err_unlock;
        }
 
-       perf_install_in_context(ctx, event, cpu);
+       err = perf_install_in_context(ctx, event, cpu);
+       WARN_ON_ONCE(err);
        perf_unpin_context(ctx);
        mutex_unlock(&ctx->mutex);
 
@@ -11297,6 +11307,7 @@ void perf_pmu_migrate_context(struct pmu *pmu, int 
src_cpu, int dst_cpu)
        struct perf_event_context *dst_ctx;
        struct perf_event *event, *tmp;
        LIST_HEAD(events);
+       int err;
 
        src_ctx = &per_cpu_ptr(pmu->pmu_cpu_context, src_cpu)->ctx;
        dst_ctx = &per_cpu_ptr(pmu->pmu_cpu_context, dst_cpu)->ctx;
@@ -11335,7 +11346,8 @@ void perf_pmu_migrate_context(struct pmu *pmu, int 
src_cpu, int dst_cpu)
                if (event->state >= PERF_EVENT_STATE_OFF)
                        event->state = PERF_EVENT_STATE_INACTIVE;
                account_event_cpu(event, dst_cpu);
-               perf_install_in_context(dst_ctx, event, dst_cpu);
+               err = perf_install_in_context(dst_ctx, event, dst_cpu);
+               WARN_ON_ONCE(err);
                get_ctx(dst_ctx);
        }
 
@@ -11348,7 +11360,8 @@ void perf_pmu_migrate_context(struct pmu *pmu, int 
src_cpu, int dst_cpu)
                if (event->state >= PERF_EVENT_STATE_OFF)
                        event->state = PERF_EVENT_STATE_INACTIVE;
                account_event_cpu(event, dst_cpu);
-               perf_install_in_context(dst_ctx, event, dst_cpu);
+               err = perf_install_in_context(dst_ctx, event, dst_cpu);
+               WARN_ON_ONCE(err);
                get_ctx(dst_ctx);
        }
        mutex_unlock(&dst_ctx->mutex);
-- 
2.22.0.709.g102302147b-goog