[PATCHv2] drivers/perf: arm-ccn: don't log to dmesg in event_init

[PATCHv2] drivers/perf: arm-ccn: don't log to dmesg in event_init

[Mark Rutland]

The ARM CCN PMU driver uses dev_warn() to complain about parameters in
the user-provided perf_event_attr. This means that under normal
operation (e.g. a single invocation of the perf tool), a number of
messages warnings may be logged to dmesg.

Tools may issue multiple syscalls to probe for feature support, and
multiple applications (from multiple users) can attempt to open events
simultaneously, so this is not very helpful, even if a user happens to
have access to dmesg. Worse, this can push important information out of
the dmesg ring buffer, and can significantly slow down syscall fuzzers,
vastly increasing the time it takes to find critical bugs.

Demote the dev_warn() instances to dev_dbg(), as is the case for all
other PMU drivers under drivers/perf/. Users who wish to debug PMU event
initialisation can enable dynamic debug to receive these messages.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
---
 drivers/perf/arm-ccn.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

Since v1 [1]:
* tidy up commit message.

Mark

[1] https://lkml.kernel.org/r/20180504104117.8086-1-mark.rutland at arm.com

diff --git a/drivers/perf/arm-ccn.c b/drivers/perf/arm-ccn.c
index 65b7e4042ece..07771e28f572 100644
--- a/drivers/perf/arm-ccn.c
+++ b/drivers/perf/arm-ccn.c
@@ -736,7 +736,7 @@ static int arm_ccn_pmu_event_init(struct perf_event *event)
 	ccn = pmu_to_arm_ccn(event->pmu);
 
 	if (hw->sample_period) {
-		dev_warn(ccn->dev, "Sampling not supported!\n");
+		dev_dbg(ccn->dev, "Sampling not supported!\n");
 		return -EOPNOTSUPP;
 	}
 
@@ -744,12 +744,12 @@ static int arm_ccn_pmu_event_init(struct perf_event *event)
 			event->attr.exclude_kernel || event->attr.exclude_hv ||
 			event->attr.exclude_idle || event->attr.exclude_host ||
 			event->attr.exclude_guest) {
-		dev_warn(ccn->dev, "Can't exclude execution levels!\n");
+		dev_dbg(ccn->dev, "Can't exclude execution levels!\n");
 		return -EINVAL;
 	}
 
 	if (event->cpu < 0) {
-		dev_warn(ccn->dev, "Can't provide per-task data!\n");
+		dev_dbg(ccn->dev, "Can't provide per-task data!\n");
 		return -EOPNOTSUPP;
 	}
 	/*
@@ -771,13 +771,13 @@ static int arm_ccn_pmu_event_init(struct perf_event *event)
 	switch (type) {
 	case CCN_TYPE_MN:
 		if (node_xp != ccn->mn_id) {
-			dev_warn(ccn->dev, "Invalid MN ID %d!\n", node_xp);
+			dev_dbg(ccn->dev, "Invalid MN ID %d!\n", node_xp);
 			return -EINVAL;
 		}
 		break;
 	case CCN_TYPE_XP:
 		if (node_xp >= ccn->num_xps) {
-			dev_warn(ccn->dev, "Invalid XP ID %d!\n", node_xp);
+			dev_dbg(ccn->dev, "Invalid XP ID %d!\n", node_xp);
 			return -EINVAL;
 		}
 		break;
@@ -785,11 +785,11 @@ static int arm_ccn_pmu_event_init(struct perf_event *event)
 		break;
 	default:
 		if (node_xp >= ccn->num_nodes) {
-			dev_warn(ccn->dev, "Invalid node ID %d!\n", node_xp);
+			dev_dbg(ccn->dev, "Invalid node ID %d!\n", node_xp);
 			return -EINVAL;
 		}
 		if (!arm_ccn_pmu_type_eq(type, ccn->node[node_xp].type)) {
-			dev_warn(ccn->dev, "Invalid type 0x%x for node %d!\n",
+			dev_dbg(ccn->dev, "Invalid type 0x%x for node %d!\n",
 					type, node_xp);
 			return -EINVAL;
 		}
@@ -808,19 +808,19 @@ static int arm_ccn_pmu_event_init(struct perf_event *event)
 		if (event_id != e->event)
 			continue;
 		if (e->num_ports && port >= e->num_ports) {
-			dev_warn(ccn->dev, "Invalid port %d for node/XP %d!\n",
+			dev_dbg(ccn->dev, "Invalid port %d for node/XP %d!\n",
 					port, node_xp);
 			return -EINVAL;
 		}
 		if (e->num_vcs && vc >= e->num_vcs) {
-			dev_warn(ccn->dev, "Invalid vc %d for node/XP %d!\n",
+			dev_dbg(ccn->dev, "Invalid vc %d for node/XP %d!\n",
 					vc, node_xp);
 			return -EINVAL;
 		}
 		valid = 1;
 	}
 	if (!valid) {
-		dev_warn(ccn->dev, "Invalid event 0x%x for node/XP %d!\n",
+		dev_dbg(ccn->dev, "Invalid event 0x%x for node/XP %d!\n",
 				event_id, node_xp);
 		return -EINVAL;
 	}
-- 
2.11.0

[PATCHv2] drivers/perf: arm-ccn: don't log to dmesg in event_init

[Kim Phillips]

[adding LKML, linux-perf-users.  Please do so from now on]

On Mon, 21 May 2018 18:19:49 +0100
Mark Rutland <mark.rutland@arm.com> wrote:

> The ARM CCN PMU driver uses dev_warn() to complain about parameters in
> the user-provided perf_event_attr. This means that under normal
> operation (e.g. a single invocation of the perf tool), a number of
> messages warnings may be logged to dmesg.
> 
> Tools may issue multiple syscalls to probe for feature support, and
> multiple applications (from multiple users) can attempt to open events
> simultaneously, so this is not very helpful, even if a user happens to
> have access to dmesg. Worse, this can push important information out of
> the dmesg ring buffer, and can significantly slow down syscall fuzzers,
> vastly increasing the time it takes to find critical bugs.
> 
> Demote the dev_warn() instances to dev_dbg(), as is the case for all
> other PMU drivers under drivers/perf/. Users who wish to debug PMU event
> initialisation can enable dynamic debug to receive these messages.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Pawel Moll <pawel.moll@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> ---

Care to address my comments to the rationale?:

https://marc.info/?l=linux-arm-kernel&m=152582291919277&w=2

Thanks,

Kim