From 547e9fd7d328af261f184bf66effc5033c886498 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 19 Jan 2011 12:51:39 +0100 Subject: [PATCH] perf: Annotate cpuctx->ctx.mutex to avoid a lockdep splat Lockdep spotted: loop_1b_instruc/1899 is trying to acquire lock: (event_mutex){+.+.+.}, at: [] perf_trace_init+0x3b/0x2f7 but task is already holding lock: (&ctx->mutex){+.+.+.}, at: [] perf_event_init_context+0xc0/0x218 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&ctx->mutex){+.+.+.}: -> #2 (cpu_hotplug.lock){+.+.+.}: -> #1 (module_mutex){+.+...}: -> #0 (event_mutex){+.+.+.}: But because the deadlock would be cpuhotplug (cpu-event) vs fork (task-event) it cannot, in fact, happen. We can annotate this by giving the perf_event_context used for the cpuctx a different lock class from those used by tasks. Signed-off-by: Peter Zijlstra LKML-Reference: Signed-off-by: Ingo Molnar --- kernel/perf_event.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 244ca3acb0ee..c5fa717cf099 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -5380,6 +5380,8 @@ free_dev: goto out; } +static struct lock_class_key cpuctx_mutex; + int perf_pmu_register(struct pmu *pmu, char *name, int type) { int cpu, ret; @@ -5428,6 +5430,7 @@ skip_type: cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu); __perf_event_init_context(&cpuctx->ctx); + lockdep_set_class(&cpuctx->ctx.mutex, &cpuctx_mutex); cpuctx->ctx.type = cpu_context; cpuctx->ctx.pmu = pmu; cpuctx->jiffies_interval = 1; -- 2.20.1