Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH] perf/core: Install cgroup event via IPI | Date | Tue, 21 Jan 2020 18:38:40 +0000 |
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> On Jan 20, 2020, at 12:50 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > 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.
Yes, this is because add_event_to_ctx() is called from wrong CPU.
> > But I'm thinking the below should also work just fine, hmm?
And yes, this also fixes it. Thanks!
Would you send official PATCH?
Song
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