Messages in this thread Patch in this message | | | Date | Mon, 20 Jan 2020 09:50:22 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] perf/core: Install cgroup event via IPI |
| |
On Thu, Jan 16, 2020 at 09:25:55AM -0800, Song Liu wrote: > cgroup events in OFF state cannot be installed without IPI, otherwise, it > may trigger the following calltrace with CONFIG_DEBUG_LIST: > > [ 31.776974] ------------[ cut here ]------------ > [ 31.777570] list_add double add: new=ffff888ff7cf0db0, prev=ffff888ff7ce82f0, next=ffff888ff7cf0db0. > [ 31.778737] WARNING: CPU: 3 PID: 1186 at lib/list_debug.c:31 __list_add_valid+0x67/0x70 > [ 31.779745] Modules linked in: > [ 31.780138] CPU: 3 PID: 1186 Comm: perf Tainted: G W 5.5.0-rc6+ #3962 > [ 31.781125] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014 > [ 31.782199] RIP: 0010:__list_add_valid+0x67/0x70
> diff --git a/kernel/events/core.c b/kernel/events/core.c > index a1f8bde19b56..36e8fe27e2a1 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -2682,14 +2682,18 @@ perf_install_in_context(struct perf_event_context *ctx, > smp_store_release(&event->ctx, ctx); > > /* > - * perf_event_attr::disabled events will not run and can be initialized > - * without IPI. Except when this is the first event for the context, in > - * that case we need the magic of the IPI to set ctx->is_active. > + * perf_event_attr::disabled events will not run and can be > + * initialized without IPI. Except: > + * 1. when this is the first event for the context, in that case > + * we need the magic of the IPI to set ctx->is_active; > + * 2. cgroup event in OFF state, because it is installed in the > + * cpuctx. > * > * The IOC_ENABLE that is sure to follow the creation of a disabled > * event will issue the IPI and reprogram the hardware. > */ > - if (__perf_effective_state(event) == PERF_EVENT_STATE_OFF && ctx->nr_events) { > + if (__perf_effective_state(event) == PERF_EVENT_STATE_OFF && > + !is_cgroup_event(event) && ctx->nr_events) { > raw_spin_lock_irq(&ctx->lock); > if (ctx->task == TASK_TOMBSTONE) { > raw_spin_unlock_irq(&ctx->lock);
I don't think this is right. Because cgroup events are always per-cpu events, ctx == &cpuctx->ctx, so the locking should work out just fine.
What does appear to be the problem is that:
add_event_to_ctx() list_update_cgroup_event() cpuctx = __get_cpu_context(ctx)
uses this_cpu_ptr() and we're now calling it from the 'wrong' CPU.
But I'm thinking the below should also work just fine, hmm?
---
diff --git a/kernel/events/core.c b/kernel/events/core.c index 2173c23c25b4..2c6134604811 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -951,9 +951,9 @@ list_update_cgroup_event(struct perf_event *event, /* * Because cgroup events are always per-cpu events, - * this will always be called from the right CPU. + * @ctx == &cpuctx->cpu. */ - cpuctx = __get_cpu_context(ctx); + cpuctx = container_of(ctx, struct perf_cpu_context, ctx); /* * Since setting cpuctx->cgrp is conditional on the current @cgrp
| |