Commit-ID: 9886167d20c0720dcfb01e62cdff4d906b226f43 Gitweb: http://git.kernel.org/tip/9886167d20c0720dcfb01e62cdff4d906b226f43 Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Thu, 3 Oct 2013 16:02:23 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Fri, 4 Oct 2013 09:58:53 +0200
perf: Fix perf_pmu_migrate_context While auditing the list_entry usage due to a trinity bug I found that perf_pmu_migrate_context violates the rules for perf_event::event_entry. The problem is that perf_event::event_entry is a RCU list element, and hence we must wait for a full RCU grace period before re-using the element after deletion. Therefore the usage in perf_pmu_migrate_context() which re-uses the entry immediately is broken. For now introduce another list_head into perf_event for this specific usage. This doesn't actually fix the trinity report because that never goes through this code. Signed-off-by: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/n/tip-mkj72lxagw1z8fvjm648i...@git.kernel.org Signed-off-by: Ingo Molnar <mi...@kernel.org> --- include/linux/perf_event.h | 24 +++++++++++++++++++++++- kernel/events/core.c | 6 +++--- 2 files changed, 26 insertions(+), 4 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 866e85c..c8ba627 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -294,9 +294,31 @@ struct ring_buffer; */ struct perf_event { #ifdef CONFIG_PERF_EVENTS - struct list_head group_entry; + /* + * entry onto perf_event_context::event_list; + * modifications require ctx->lock + * RCU safe iterations. + */ struct list_head event_entry; + + /* + * XXX: group_entry and sibling_list should be mutually exclusive; + * either you're a sibling on a group, or you're the group leader. + * Rework the code to always use the same list element. + * + * Locked for modification by both ctx->mutex and ctx->lock; holding + * either sufficies for read. + */ + struct list_head group_entry; struct list_head sibling_list; + + /* + * We need storage to track the entries in perf_pmu_migrate_context; we + * cannot use the event_entry because of RCU and we want to keep the + * group in tact which avoids us using the other two entries. + */ + struct list_head migrate_entry; + struct hlist_node hlist_entry; int nr_siblings; int group_flags; diff --git a/kernel/events/core.c b/kernel/events/core.c index cb4238e..d49a9d2 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -7234,15 +7234,15 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu) perf_remove_from_context(event); unaccount_event_cpu(event, src_cpu); put_ctx(src_ctx); - list_add(&event->event_entry, &events); + list_add(&event->migrate_entry, &events); } mutex_unlock(&src_ctx->mutex); synchronize_rcu(); mutex_lock(&dst_ctx->mutex); - list_for_each_entry_safe(event, tmp, &events, event_entry) { - list_del(&event->event_entry); + list_for_each_entry_safe(event, tmp, &events, migrate_entry) { + list_del(&event->migrate_entry); if (event->state >= PERF_EVENT_STATE_OFF) event->state = PERF_EVENT_STATE_INACTIVE; account_event_cpu(event, dst_cpu); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
