On Tue, Mar 14, 2017 at 02:24:27PM +0100, Oleg Nesterov wrote: > On 03/14, Peter Zijlstra wrote: > > > > On Tue, Mar 07, 2017 at 05:51:32PM +0100, Oleg Nesterov wrote: > > > > > inherit_event() returns NULL under is_orphaned_event() check, not > > > ERR_PTR(). > > > Is it correct? > > > > Yes. This is all a tad tricky, but it seems to be correct. > > > > By returning NULL, not an error, we affect the silent discard of > > orphaned events. This is correct, because otherwise > > perf_event_release_kernel() would have come by and explicitly discarded > > those events for us anyway. > > Thanks... I'll try to understand this later. > > > @@ -10608,7 +10627,6 @@ inherit_task_group(struct perf_event *event, struct > > task_struct *parent, > > * First allocate and initialize a context for the > > * child. > > */ > > - > > child_ctx = alloc_perf_context(parent_ctx->pmu, child); > > if (!child_ctx) > > return -ENOMEM; > > @@ -10670,7 +10688,7 @@ static int perf_event_init_context(struct > > task_struct *child, int ctxn) > > ret = inherit_task_group(event, parent, parent_ctx, > > child, ctxn, &inherited_all); > > if (ret) > > - break; > > + goto out_unlock; > > } > > > > /* > > @@ -10686,7 +10704,7 @@ static int perf_event_init_context(struct > > task_struct *child, int ctxn) > > ret = inherit_task_group(event, parent, parent_ctx, > > child, ctxn, &inherited_all); > > if (ret) > > - break; > > + goto out_unlock; > > With this change you can also simplify inherit_task_group() a little bit, > it no longer needs to nullify *inherited_all if inherit_group() fails.
Ah, that last one is broken because then we forget to re-enable parent_ctx->rotate_disable. So if we keep that a break, we still need that inherited_all thing as well.
