diff options
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/events/core.c | 83 |
1 files changed, 63 insertions, 20 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 785d708f8553..eea9d52b010c 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2553,6 +2553,9 @@ unlock: return ret; } +static bool exclusive_event_installable(struct perf_event *event, + struct perf_event_context *ctx); + /* * Attach a performance event to a context. * @@ -2567,6 +2570,8 @@ perf_install_in_context(struct perf_event_context *ctx, lockdep_assert_held(&ctx->mutex); + WARN_ON_ONCE(!exclusive_event_installable(event, ctx)); + if (event->cpu != -1) event->cpu = cpu; @@ -4360,7 +4365,7 @@ static int exclusive_event_init(struct perf_event *event) { struct pmu *pmu = event->pmu; - if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE)) + if (!is_exclusive_pmu(pmu)) return 0; /* @@ -4391,7 +4396,7 @@ static void exclusive_event_destroy(struct perf_event *event) { struct pmu *pmu = event->pmu; - if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE)) + if (!is_exclusive_pmu(pmu)) return; /* see comment in exclusive_event_init() */ @@ -4411,14 +4416,15 @@ static bool exclusive_event_match(struct perf_event *e1, struct perf_event *e2) return false; } -/* Called under the same ctx::mutex as perf_install_in_context() */ static bool exclusive_event_installable(struct perf_event *event, struct perf_event_context *ctx) { struct perf_event *iter_event; struct pmu *pmu = event->pmu; - if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE)) + lockdep_assert_held(&ctx->mutex); + + if (!is_exclusive_pmu(pmu)) return true; list_for_each_entry(iter_event, &ctx->event_list, event_entry) { @@ -4465,12 +4471,20 @@ static void _free_event(struct perf_event *event) if (event->destroy) event->destroy(event); - if (event->ctx) - put_ctx(event->ctx); - + /* + * Must be after ->destroy(), due to uprobe_perf_close() using + * hw.target. + */ if (event->hw.target) put_task_struct(event->hw.target); + /* + * 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); @@ -4650,8 +4664,17 @@ again: mutex_unlock(&event->child_mutex); list_for_each_entry_safe(child, tmp, &free_list, child_list) { + void *var = &child->ctx->refcount; + list_del(&child->child_list); free_event(child); + + /* + * Wake any perf_event_free_task() waiting for this event to be + * freed. + */ + smp_mb(); /* pairs with wait_var_event() */ + wake_up_var(var); } no_ctx: @@ -10930,11 +10953,6 @@ SYSCALL_DEFINE5(perf_event_open, goto err_alloc; } - if ((pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE) && group_leader) { - err = -EBUSY; - goto err_context; - } - /* * Look up the group leader (we will attach this event to it): */ @@ -11022,6 +11040,18 @@ SYSCALL_DEFINE5(perf_event_open, move_group = 0; } } + + /* + * Failure to create exclusive events returns -EBUSY. + */ + err = -EBUSY; + if (!exclusive_event_installable(group_leader, ctx)) + goto err_locked; + + for_each_sibling_event(sibling, group_leader) { + if (!exclusive_event_installable(sibling, ctx)) + goto err_locked; + } } else { mutex_lock(&ctx->mutex); } @@ -11058,9 +11088,6 @@ SYSCALL_DEFINE5(perf_event_open, * because we need to serialize with concurrent event creation. */ if (!exclusive_event_installable(event, ctx)) { - /* exclusive and group stuff are assumed mutually exclusive */ - WARN_ON_ONCE(move_group); - err = -EBUSY; goto err_locked; } @@ -11527,11 +11554,11 @@ static void perf_free_event(struct perf_event *event, } /* - * Free an unexposed, unused context as created by inheritance by - * perf_event_init_task below, used by fork() in case of fail. + * Free a context as created by inheritance by perf_event_init_task() below, + * used by fork() in case of fail. * - * Not all locks are strictly required, but take them anyway to be nice and - * help out with the lockdep assertions. + * Even though the task has never lived, the context and events have been + * exposed through the child_list, so we must take care tearing it all down. */ void perf_event_free_task(struct task_struct *task) { @@ -11561,7 +11588,23 @@ void perf_event_free_task(struct task_struct *task) perf_free_event(event, ctx); mutex_unlock(&ctx->mutex); - put_ctx(ctx); + + /* + * perf_event_release_kernel() could've stolen some of our + * child events and still have them on its free_list. In that + * case we must wait for these events to have been freed (in + * particular all their references to this task must've been + * dropped). + * + * Without this copy_process() will unconditionally free this + * task (irrespective of its reference count) and + * _free_event()'s put_task_struct(event->hw.target) will be a + * use-after-free. + * + * Wait for all events to drop their context reference. + */ + wait_var_event(&ctx->refcount, refcount_read(&ctx->refcount) == 1); + put_ctx(ctx); /* must be last */ } } |