linux-kernel - Re: x86_pmu_start WARN

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Message-ID: <20140220182300.GN9987@twins.programming.kicks-ass.net>
Date:	Thu, 20 Feb 2014 19:23:00 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: x86_pmu_start WARN_ON.

On Thu, Feb 20, 2014 at 01:03:16PM -0500, Vince Weaver wrote:
> attached, it's not very big.

This is I think the relevant bit:

   pec_1076_warn-2804  [000] d...   147.926153: x86_pmu_disable: x86_pmu_disable
   pec_1076_warn-2804  [000] d...   147.926153: x86_pmu_state: Events: {
   pec_1076_warn-2804  [000] d...   147.926156: x86_pmu_state:   0: state: .R config: ffffffffffffffff (          (null))
   pec_1076_warn-2804  [000] d...   147.926158: x86_pmu_state:   33: state: AR config: 0 (ffff88011ac99800)
   pec_1076_warn-2804  [000] d...   147.926159: x86_pmu_state: }
   pec_1076_warn-2804  [000] d...   147.926160: x86_pmu_state: n_events: 1, n_added: 0, n_txn: 1
   pec_1076_warn-2804  [000] d...   147.926161: x86_pmu_state: Assignment: {
   pec_1076_warn-2804  [000] d...   147.926162: x86_pmu_state:   0->33 tag: 1 config: 0 (ffff88011ac99800)
   pec_1076_warn-2804  [000] d...   147.926163: x86_pmu_state: }
   pec_1076_warn-2804  [000] d...   147.926166: collect_events: Adding event: 1 (ffff880119ec8800)
   pec_1076_warn-2804  [000] d...   147.926170: collect_events: Adding event: 0 (ffff8800c9e01800)
   pec_1076_warn-2804  [000] d...   147.926172: collect_events: Adding event: 4 (ffff8800cbab2c00)
   pec_1076_warn-2804  [000] d...   147.926177: x86_pmu_enable: x86_pmu_enable
   pec_1076_warn-2804  [000] d...   147.926177: x86_pmu_state: Events: {
   pec_1076_warn-2804  [000] d...   147.926179: x86_pmu_state:   0: state: .R config: ffffffffffffffff (          (null))
   pec_1076_warn-2804  [000] d...   147.926181: x86_pmu_state:   33: state: AR config: 0 (ffff88011ac99800)
   pec_1076_warn-2804  [000] d...   147.926182: x86_pmu_state: }
   pec_1076_warn-2804  [000] d...   147.926184: x86_pmu_state: n_events: 2, n_added: 2, n_txn: 2
   pec_1076_warn-2804  [000] d...   147.926184: x86_pmu_state: Assignment: {
   pec_1076_warn-2804  [000] d...   147.926186: x86_pmu_state:   0->33 tag: 1 config: 0 (ffff88011ac99800)
   pec_1076_warn-2804  [000] d...   147.926188: x86_pmu_state:   1->0 tag: 1 config: 1 (ffff880119ec8800)
   pec_1076_warn-2804  [000] d...   147.926188: x86_pmu_state: }
   pec_1076_warn-2804  [000] d...   147.926190: x86_pmu_enable: S0: hwc->idx: 33, hwc->last_cpu: 0, hwc->last_tag: 1 hwc->state: 0
   pec_1076_warn-2804  [000] d...   147.926191: x86_pmu_enable: starting: 0

so it does indeed look like n_added got scrambled; we started out with 1
event on disable; we've got 2 events on enable, but n_added is also 2,
which would suggest we had 0 on disable.

That makes us want to (re)start the NMI counter alright.

I've got to go run errands for a bit; hopefully I can find a bit of time
later tonight to look this over.
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