[PATCH] coresight: etm_perf: Rework alloc/free methods to avoid lockep warning
From: Mathieu Poirier
Date: Wed Jul 18 2018 - 15:43:55 EST
When enabling the lockdep mechanic and working with CPU-wide scenarios we
get the following console output:
[ 54.632093] ======================================================
[ 54.638207] WARNING: possible circular locking dependency detected
[ 54.644322] 4.18.0-rc3-00042-g2d39e6356bb7-dirty #309 Not tainted
[ 54.650350] ------------------------------------------------------
[ 54.656464] perf/2862 is trying to acquire lock:
[ 54.661031] 000000007e21d170 (&event->mmap_mutex){+.+.}, at: perf_event_set_output+0x98/0x138
[ 54.669486]
[ 54.669486] but task is already holding lock:
[ 54.675256] 000000001080eb1b (&cpuctx_mutex){+.+.}, at: perf_event_ctx_lock_nested+0xf8/0x1f0
[ 54.683704]
[ 54.683704] which lock already depends on the new lock.
[ 54.683704]
[ 54.691797]
[ 54.691797] the existing dependency chain (in reverse order) is:
[ 54.699201]
[ 54.699201] -> #3 (&cpuctx_mutex){+.+.}:
[ 54.704556] __mutex_lock+0x70/0x808
[ 54.708608] mutex_lock_nested+0x1c/0x28
[ 54.713005] perf_event_init_cpu+0x8c/0xd8
[ 54.717574] perf_event_init+0x194/0x1d4
[ 54.721971] start_kernel+0x2b8/0x42c
[ 54.726107]
[ 54.726107] -> #2 (pmus_lock){+.+.}:
[ 54.731114] __mutex_lock+0x70/0x808
[ 54.735165] mutex_lock_nested+0x1c/0x28
[ 54.739560] perf_event_init_cpu+0x30/0xd8
[ 54.744129] cpuhp_invoke_callback+0x84/0x248
[ 54.748954] _cpu_up+0xe8/0x1c8
[ 54.752576] do_cpu_up+0xa8/0xc8
[ 54.756283] cpu_up+0x10/0x18
[ 54.759731] smp_init+0xa0/0x114
[ 54.763438] kernel_init_freeable+0x120/0x288
[ 54.768264] kernel_init+0x10/0x108
[ 54.772230] ret_from_fork+0x10/0x18
[ 54.776279]
[ 54.776279] -> #1 (cpu_hotplug_lock.rw_sem){++++}:
[ 54.782492] cpus_read_lock+0x34/0xb0
[ 54.786631] etm_setup_aux+0x5c/0x308
[ 54.790769] rb_alloc_aux+0x1ec/0x300
[ 54.794906] perf_mmap+0x284/0x610
[ 54.798787] mmap_region+0x388/0x570
[ 54.802838] do_mmap+0x344/0x4f8
[ 54.806544] vm_mmap_pgoff+0xe4/0x110
[ 54.810682] ksys_mmap_pgoff+0xa8/0x240
[ 54.814992] sys_mmap+0x18/0x28
[ 54.818613] el0_svc_naked+0x30/0x34
[ 54.822661]
[ 54.822661] -> #0 (&event->mmap_mutex){+.+.}:
[ 54.828445] lock_acquire+0x48/0x68
[ 54.832409] __mutex_lock+0x70/0x808
[ 54.836459] mutex_lock_nested+0x1c/0x28
[ 54.840855] perf_event_set_output+0x98/0x138
[ 54.845680] _perf_ioctl+0x2a0/0x6a0
[ 54.849731] perf_ioctl+0x3c/0x68
[ 54.853526] do_vfs_ioctl+0xb8/0xa20
[ 54.857577] ksys_ioctl+0x80/0xb8
[ 54.861370] sys_ioctl+0xc/0x18
[ 54.864990] el0_svc_naked+0x30/0x34
[ 54.869039]
[ 54.869039] other info that might help us debug this:
[ 54.869039]
[ 54.876960] Chain exists of:
[ 54.876960] &event->mmap_mutex --> pmus_lock --> &cpuctx_mutex
[ 54.876960]
[ 54.887217] Possible unsafe locking scenario:
[ 54.887217]
[ 54.893073] CPU0 CPU1
[ 54.897552] ---- ----
[ 54.902030] lock(&cpuctx_mutex);
[ 54.905396] lock(pmus_lock);
[ 54.910911] lock(&cpuctx_mutex);
[ 54.916770] lock(&event->mmap_mutex);
[ 54.920566]
[ 54.920566] *** DEADLOCK ***
[ 54.920566]
[ 54.926424] 1 lock held by perf/2862:
[ 54.930042] #0: 000000001080eb1b (&cpuctx_mutex){+.+.}, at: perf_event_ctx_lock_nested+0xf8/0x1f0
This is fixed by working with the cpu_present_mask, avoinding at the same
the need to use get/put_online_cpus() that triggers lockdep.
Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
---
drivers/hwtracing/coresight/coresight-etm-perf.c | 39 +++++++++++++-----------
1 file changed, 21 insertions(+), 18 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 677695635211..16b9c87d9d00 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -108,26 +108,32 @@ static int etm_event_init(struct perf_event *event)
static void free_event_data(struct work_struct *work)
{
int cpu;
+ void *snk_config;
cpumask_t *mask;
struct etm_event_data *event_data;
struct coresight_device *sink;
event_data = container_of(work, struct etm_event_data, work);
mask = &event_data->mask;
- /*
- * First deal with the sink configuration. See comment in
- * etm_setup_aux() about why we take the first available path.
- */
- if (event_data->snk_config) {
- cpu = cpumask_first(mask);
- sink = coresight_get_sink(event_data->path[cpu]);
- if (sink_ops(sink)->free_buffer)
- sink_ops(sink)->free_buffer(event_data->snk_config);
- }
+ snk_config = event_data->snk_config;
for_each_cpu(cpu, mask) {
- if (!(IS_ERR_OR_NULL(event_data->path[cpu])))
- coresight_release_path(event_data->path[cpu]);
+ if (IS_ERR_OR_NULL(event_data->path[cpu]))
+ continue;
+
+ /*
+ * Free sink configuration - there can only be one sink
+ * per event.
+ */
+ if (snk_config) {
+ sink = coresight_get_sink(event_data->path[cpu]);
+ if (sink_ops(sink)->free_buffer) {
+ sink_ops(sink)->free_buffer(snk_config);
+ snk_config = NULL;
+ }
+ }
+
+ coresight_release_path(event_data->path[cpu]);
}
kfree(event_data->path);
@@ -145,16 +151,13 @@ static void *alloc_event_data(int cpu)
if (!event_data)
return NULL;
- /* Make sure nothing disappears under us */
- get_online_cpus();
- size = num_online_cpus();
-
mask = &event_data->mask;
+ size = num_present_cpus();
+
if (cpu != -1)
cpumask_set_cpu(cpu, mask);
else
- cpumask_copy(mask, cpu_online_mask);
- put_online_cpus();
+ cpumask_copy(mask, cpu_present_mask);
/*
* Each CPU has a single path between source and destination. As such
--
2.7.4