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Message-ID: <87fupul0bp.fsf@ashishki-desk.ger.corp.intel.com>
Date: Wed, 24 Aug 2016 17:15:54 +0300
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To: vince@...ter.net, Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
eranian@...gle.com, Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH 1/3] perf/x86/intel/bts: Fix confused ordering of PMU callbacks
Alexander Shishkin <alexander.shishkin@...ux.intel.com> writes:
> Alexander Shishkin <alexander.shishkin@...ux.intel.com> writes:
>
>> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
>
> Ok, this one is broken, please disregard.
Vince, can you try the following (with the other two in this series)?
---
>From 68713194b3df8e565c4d319a80e9e7338fa1ec13 Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Date: Tue, 23 Aug 2016 10:50:57 +0300
Subject: [PATCH] perf/x86/intel/bts: Fix confused ordering of PMU callbacks
The intel_bts driver is using a cpu-local 'started' variable to order
callbacks and PMIs and make sure that AUX transactions don't get messed
up. However, the ordering rules in regard to this variable is a complete
mess, which recently resulted in perf_fuzzer-triggered warnings and
panics.
The general ordering rule that is patch is enforcing is that this
cpu-local variable be set only when the cpu-local AUX transaction is
active; consequently, this variable is to be checked before the AUX
related bits can be touched.
Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
---
arch/x86/events/intel/bts.c | 119 +++++++++++++++++++++++++++++++++++---------
1 file changed, 96 insertions(+), 23 deletions(-)
diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 0a6e393a2e..13ce76e895 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -31,7 +31,18 @@
struct bts_ctx {
struct perf_output_handle handle;
struct debug_store ds_back;
- int started;
+ local_t pmi_pending;
+ int state;
+};
+
+/* BTS context states: */
+enum {
+ /* no ongoing AUX transactions */
+ BTS_STATE_STOPPED = 0,
+ /* AUX transaction is on, BTS tracing is disabled */
+ BTS_STATE_INACTIVE,
+ /* AUX transaction is on, BTS tracing is running */
+ BTS_STATE_ACTIVE,
};
static DEFINE_PER_CPU(struct bts_ctx, bts_ctx);
@@ -191,6 +202,9 @@ static void bts_update(struct bts_ctx *bts)
if (ds->bts_index >= ds->bts_absolute_maximum)
local_inc(&buf->lost);
+ if (ds->bts_index >= ds->bts_interrupt_threshold)
+ local_inc(&bts->pmi_pending);
+
/*
* old and head are always in the same physical buffer, so we
* can subtract them to get the data size.
@@ -204,6 +218,16 @@ static void bts_update(struct bts_ctx *bts)
static int
bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle);
+/*
+ * Ordering PMU callbacks wrt themselves and the PMI is done by means
+ * of bts::state, which:
+ * - is set when bts::handle::event is valid, that is, between
+ * perf_aux_output_begin() and perf_aux_output_end();
+ * - is zero otherwise;
+ * - is ordered against bts::handle::event with a local barrier to
+ * enforce CPU ordering.
+ */
+
static void __bts_event_start(struct perf_event *event)
{
struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
@@ -221,10 +245,13 @@ static void __bts_event_start(struct perf_event *event)
/*
* local barrier to make sure that ds configuration made it
- * before we enable BTS
+ * before we enable BTS and bts::state goes ACTIVE
*/
wmb();
+ /* INACTIVE/STOPPED -> ACTIVE */
+ WRITE_ONCE(bts->state, BTS_STATE_ACTIVE);
+
intel_pmu_enable_bts(config);
}
@@ -251,9 +278,6 @@ static void bts_event_start(struct perf_event *event, int flags)
__bts_event_start(event);
- /* PMI handler: this counter is running and likely generating PMIs */
- ACCESS_ONCE(bts->started) = 1;
-
return;
fail_end_stop:
@@ -265,28 +289,36 @@ fail_stop:
static void __bts_event_stop(struct perf_event *event)
{
+ struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+
+ /* ACTIVE -> INACTIVE */
+ WRITE_ONCE(bts->state, BTS_STATE_INACTIVE);
+
/*
* No extra synchronization is mandated by the documentation to have
* BTS data stores globally visible.
*/
intel_pmu_disable_bts();
-
- if (event->hw.state & PERF_HES_STOPPED)
- return;
-
- ACCESS_ONCE(event->hw.state) |= PERF_HES_STOPPED;
}
static void bts_event_stop(struct perf_event *event, int flags)
{
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
- struct bts_buffer *buf = perf_get_aux(&bts->handle);
+ struct bts_buffer *buf;
+
+ if (READ_ONCE(bts->state) == BTS_STATE_ACTIVE)
+ __bts_event_stop(event);
+
+ /*
+ * order buf (handle::event load) against bts::state store;
+ * matches wmb() in intel_bts_interrupt()
+ */
+ mb();
- /* PMI handler: don't restart this counter */
- ACCESS_ONCE(bts->started) = 0;
+ buf = perf_get_aux(&bts->handle);
- __bts_event_stop(event);
+ event->hw.state |= PERF_HES_STOPPED;
if (flags & PERF_EF_UPDATE) {
bts_update(bts);
@@ -298,6 +330,11 @@ static void bts_event_stop(struct perf_event *event, int flags)
buf->nr_pages << PAGE_SHIFT);
perf_aux_output_end(&bts->handle, local_xchg(&buf->data_size, 0),
!!local_xchg(&buf->lost, 0));
+ /*
+ * no need to enforce ordering here as the PMI won't come after
+ * __bts_event_stop()+mb() above
+ */
+ WRITE_ONCE(bts->state, BTS_STATE_STOPPED);
}
cpuc->ds->bts_index = bts->ds_back.bts_buffer_base;
@@ -311,7 +348,13 @@ void intel_bts_enable_local(void)
{
struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
- if (bts->handle.event && bts->started)
+ if (READ_ONCE(bts->state) == BTS_STATE_ACTIVE)
+ return;
+
+ /* matches wmb() ordering bts::state store against handle::event */
+ rmb();
+
+ if (bts->handle.event)
__bts_event_start(bts->handle.event);
}
@@ -319,6 +362,12 @@ void intel_bts_disable_local(void)
{
struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+ if (READ_ONCE(bts->state) == BTS_STATE_INACTIVE)
+ return;
+
+ /* matches wmb() ordering bts::state store against handle::event */
+ rmb();
+
if (bts->handle.event)
__bts_event_stop(bts->handle.event);
}
@@ -407,10 +456,25 @@ int intel_bts_interrupt(void)
struct perf_event *event = bts->handle.event;
struct bts_buffer *buf;
s64 old_head;
- int err;
+ int err = -ENOSPC, handled = 0;
- if (!event || !bts->started)
- return 0;
+ if (local_read(&bts->pmi_pending)) {
+ handled = 1;
+ local_set(&bts->pmi_pending, 0);
+ }
+
+ /*
+ * this is wrapped in intel_bts_enable_local/intel_bts_disable_local,
+ * so we can only be INACTIVE or STOPPED
+ */
+ if (READ_ONCE(bts->state) == BTS_STATE_STOPPED)
+ return handled;
+
+ /* matches wmb() ordering bts::state store against handle::event */
+ rmb();
+
+ if (!event)
+ return handled;
buf = perf_get_aux(&bts->handle);
/*
@@ -432,12 +496,21 @@ int intel_bts_interrupt(void)
!!local_xchg(&buf->lost, 0));
buf = perf_aux_output_begin(&bts->handle, event);
- if (!buf)
- return 1;
+ if (buf)
+ err = bts_buffer_reset(buf, &bts->handle);
+
+ if (err) {
+ WRITE_ONCE(bts->state, BTS_STATE_STOPPED);
- err = bts_buffer_reset(buf, &bts->handle);
- if (err)
- perf_aux_output_end(&bts->handle, 0, false);
+ if (buf) {
+ /*
+ * BTS_STATE_STOPPED should be visible before
+ * cleared handle::event
+ */
+ wmb();
+ perf_aux_output_end(&bts->handle, 0, false);
+ }
+ }
return 1;
}
--
2.8.1
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