[PATCH v5 03/11] PM / QoS: Fix constraints alloc vs reclaim locking

Rob Clark
2023-08-22T18:02:41Z

In the process of adding lockdep annotation for drm GPU scheduler's
job_run() to detect potential deadlock against shrinker/reclaim, I hit
this lockdep splat:

======================================================
WARNING: possible circular locking dependency detected
6.2.0-rc8-debug+ #558 Tainted: G W
------------------------------------------------------
ring0/125 is trying to acquire lock:
ffffffd6d6ce0f28 (dev_pm_qos_mtx){+.+.}-{3:3}, at: dev_pm_qos_update_request+0x38/0x68

but task is already holding lock:
ffffff8087239208 (&gpu->active_lock){+.+.}-{3:3}, at: msm_gpu_submit+0xec/0x178

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #4 (&gpu->active_lock){+.+.}-{3:3}:
__mutex_lock+0xcc/0x3c8
mutex_lock_nested+0x30/0x44
msm_gpu_submit+0xec/0x178
msm_job_run+0x78/0x150
drm_sched_main+0x290/0x370
kthread+0xf0/0x100
ret_from_fork+0x10/0x20

-> #3 (dma_fence_map){++++}-{0:0}:
__dma_fence_might_wait+0x74/0xc0
dma_resv_lockdep+0x1f4/0x2f4
do_one_initcall+0x104/0x2bc
kernel_init_freeable+0x344/0x34c
kernel_init+0x30/0x134
ret_from_fork+0x10/0x20

-> #2 (mmu_notifier_invalidate_range_start){+.+.}-{0:0}:
fs_reclaim_acquire+0x80/0xa8
slab_pre_alloc_hook.constprop.0+0x40/0x25c
__kmem_cache_alloc_node+0x60/0x1cc
__kmalloc+0xd8/0x100
topology_parse_cpu_capacity+0x8c/0x178
get_cpu_for_node+0x88/0xc4
parse_cluster+0x1b0/0x28c
parse_cluster+0x8c/0x28c
init_cpu_topology+0x168/0x188
smp_prepare_cpus+0x24/0xf8
kernel_init_freeable+0x18c/0x34c
kernel_init+0x30/0x134
ret_from_fork+0x10/0x20

-> #1 (fs_reclaim){+.+.}-{0:0}:
__fs_reclaim_acquire+0x3c/0x48
fs_reclaim_acquire+0x54/0xa8
slab_pre_alloc_hook.constprop.0+0x40/0x25c
__kmem_cache_alloc_node+0x60/0x1cc
kmalloc_trace+0x50/0xa8
dev_pm_qos_constraints_allocate+0x38/0x100
__dev_pm_qos_add_request+0xb0/0x1e8
dev_pm_qos_add_request+0x58/0x80
dev_pm_qos_expose_latency_limit+0x60/0x13c
register_cpu+0x12c/0x130
topology_init+0xac/0xbc
do_one_initcall+0x104/0x2bc
kernel_init_freeable+0x344/0x34c
kernel_init+0x30/0x134
ret_from_fork+0x10/0x20

-> #0 (dev_pm_qos_mtx){+.+.}-{3:3}:
__lock_acquire+0xe00/0x1060
lock_acquire+0x1e0/0x2f8
__mutex_lock+0xcc/0x3c8
mutex_lock_nested+0x30/0x44
dev_pm_qos_update_request+0x38/0x68
msm_devfreq_boost+0x40/0x70
msm_devfreq_active+0xc0/0xf0
msm_gpu_submit+0x10c/0x178
msm_job_run+0x78/0x150
drm_sched_main+0x290/0x370
kthread+0xf0/0x100
ret_from_fork+0x10/0x20

other info that might help us debug this:

Chain exists of:
dev_pm_qos_mtx --> dma_fence_map --> &gpu->active_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&gpu->active_lock);
lock(dma_fence_map);
lock(&gpu->active_lock);
lock(dev_pm_qos_mtx);

*** DEADLOCK ***

3 locks held by ring0/123:
#0: ffffff8087251170 (&gpu->lock){+.+.}-{3:3}, at: msm_job_run+0x64/0x150
#1: ffffffd00b0e57e8 (dma_fence_map){++++}-{0:0}, at: msm_job_run+0x68/0x150
#2: ffffff8087251208 (&gpu->active_lock){+.+.}-{3:3}, at: msm_gpu_submit+0xec/0x178

stack backtrace:
CPU: 6 PID: 123 Comm: ring0 Not tainted 6.2.0-rc8-debug+ #559
Hardware name: Google Lazor (rev1 - 2) with LTE (DT)
Call trace:
dump_backtrace.part.0+0xb4/0xf8
show_stack+0x20/0x38
dump_stack_lvl+0x9c/0xd0
dump_stack+0x18/0x34
print_circular_bug+0x1b4/0x1f0
check_noncircular+0x78/0xac
__lock_acquire+0xe00/0x1060
lock_acquire+0x1e0/0x2f8
__mutex_lock+0xcc/0x3c8
mutex_lock_nested+0x30/0x44
dev_pm_qos_update_request+0x38/0x68
msm_devfreq_boost+0x40/0x70
msm_devfreq_active+0xc0/0xf0
msm_gpu_submit+0x10c/0x178
msm_job_run+0x78/0x150
drm_sched_main+0x290/0x370
kthread+0xf0/0x100
ret_from_fork+0x10/0x20

The issue is that dev_pm_qos_mtx is held in the runpm suspend/resume (or
freq change) path, but it is also held across allocations that could
recurse into shrinker.

Solve this by changing dev_pm_qos_constraints_allocate() into a function
that can be called unconditionally before the device qos object is
needed and before aquiring dev_pm_qos_mtx. This way the allocations can
be done without holding the mutex. In the case that we raced with
another thread to allocate the qos object, detect this *after* acquiring
the dev_pm_qos_mtx and simply free the redundant allocations.

Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
---
drivers/base/power/qos.c | 76 +++++++++++++++++++++++++++++-----------
1 file changed, 56 insertions(+), 20 deletions(-)

diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
index 8e93167f1783..7e95760d16dc 100644
--- a/drivers/base/power/qos.c
+++ b/drivers/base/power/qos.c
@@ -185,27 +185,33 @@ static int apply_constraint(struct dev_pm_qos_request *req,
}

/*
- * dev_pm_qos_constraints_allocate
+ * dev_pm_qos_constraints_allocate: Allocate and initializes qos constraints
* @dev: device to allocate data for
*
- * Called at the first call to add_request, for constraint data allocation
- * Must be called with the dev_pm_qos_mtx mutex held
+ * Called to allocate constraints before dev_pm_qos_mtx mutex is held. Should
+ * be matched with a call to dev_pm_qos_constraints_set() once dev_pm_qos_mtx
+ * is held.
*/
-static int dev_pm_qos_constraints_allocate(struct device *dev)
+static struct dev_pm_qos *dev_pm_qos_constraints_allocate(struct device *dev)
{
struct dev_pm_qos *qos;
struct pm_qos_constraints *c;
struct blocking_notifier_head *n;

- qos = kzalloc(sizeof(*qos), GFP_KERNEL);
+ /*
+ * If constraints are already allocated, we can skip speculatively
+ * allocating a new one, as we don't have to work about qos transitioning
+ * from non-null to null. The constraints are only freed on device
+ * removal.
+ */
+ if (dev->power.qos)
+ return NULL;
+
+ qos = kzalloc(sizeof(*qos) + 3 * sizeof(*n), GFP_KERNEL);
if (!qos)
- return -ENOMEM;
+ return NULL;

- n = kzalloc(3 * sizeof(*n), GFP_KERNEL);
- if (!n) {
- kfree(qos);
- return -ENOMEM;
- }
+ n = (struct blocking_notifier_head *)(qos + 1);

c = &qos->resume_latency;
plist_head_init(&c->list);
@@ -227,11 +233,29 @@ static int dev_pm_qos_constraints_allocate(struct device *dev)

INIT_LIST_HEAD(&qos->flags.list);

+ return qos;
+}
+
+/*
+ * dev_pm_qos_constraints_set: Ensure dev->power.qos is set
+ *
+ * If dev->power.qos is already set, free the newly allocated qos constraints.
+ * Otherwise set dev->power.qos. Must be called with dev_pm_qos_mtx held.
+ *
+ * This split unsynchronized allocation and synchronized set moves allocation
+ * out from under dev_pm_qos_mtx, so that lockdep does does not get angry about
+ * drivers which use dev_pm_qos in paths related to shrinker/reclaim.
+ */
+static void dev_pm_qos_constraints_set(struct device *dev, struct dev_pm_qos *qos)
+{
+ if (dev->power.qos) {
+ kfree(qos);
+ return;
+ }
+
spin_lock_irq(&dev->power.lock);
dev->power.qos = qos;
spin_unlock_irq(&dev->power.lock);
-
- return 0;
}

static void __dev_pm_qos_hide_latency_limit(struct device *dev);
@@ -309,7 +333,6 @@ void dev_pm_qos_constraints_destroy(struct device *dev)
dev->power.qos = ERR_PTR(-ENODEV);
spin_unlock_irq(&dev->power.lock);

- kfree(qos->resume_latency.notifiers);
kfree(qos);

out:
@@ -341,7 +364,7 @@ static int __dev_pm_qos_add_request(struct device *dev,
if (IS_ERR(dev->power.qos))
ret = -ENODEV;
else if (!dev->power.qos)
- ret = dev_pm_qos_constraints_allocate(dev);
+ ret = -ENOMEM;

trace_dev_pm_qos_add_request(dev_name(dev), type, value);
if (ret)
@@ -388,9 +411,11 @@ static int __dev_pm_qos_add_request(struct device *dev,
int dev_pm_qos_add_request(struct device *dev, struct dev_pm_qos_request *req,
enum dev_pm_qos_req_type type, s32 value)
{
+ struct dev_pm_qos *qos = dev_pm_qos_constraints_allocate(dev);
int ret;

mutex_lock(&dev_pm_qos_mtx);
+ dev_pm_qos_constraints_set(dev, qos);
ret = __dev_pm_qos_add_request(dev, req, type, value);
mutex_unlock(&dev_pm_qos_mtx);
return ret;
@@ -535,14 +560,15 @@ EXPORT_SYMBOL_GPL(dev_pm_qos_remove_request);
int dev_pm_qos_add_notifier(struct device *dev, struct notifier_block *notifier,
enum dev_pm_qos_req_type type)
{
+ struct dev_pm_qos *qos = dev_pm_qos_constraints_allocate(dev);
int ret = 0;

mutex_lock(&dev_pm_qos_mtx);

+ dev_pm_qos_constraints_set(dev, qos);
+
if (IS_ERR(dev->power.qos))
ret = -ENODEV;
- else if (!dev->power.qos)
- ret = dev_pm_qos_constraints_allocate(dev);

if (ret)
goto unlock;
@@ -903,12 +929,22 @@ s32 dev_pm_qos_get_user_latency_tolerance(struct device *dev)
*/
int dev_pm_qos_update_user_latency_tolerance(struct device *dev, s32 val)
{
- int ret;
+ struct dev_pm_qos *qos = dev_pm_qos_constraints_allocate(dev);
+ int ret = 0;

mutex_lock(&dev_pm_qos_mtx);

- if (IS_ERR_OR_NULL(dev->power.qos)
- || !dev->power.qos->latency_tolerance_req) {
+ dev_pm_qos_constraints_set(dev, qos);
+
+ if (IS_ERR(dev->power.qos))
+ ret = -ENODEV;
+ else if (!dev->power.qos)
+ ret = -ENOMEM;
+
+ if (ret)
+ goto out;
+
+ if (!dev->power.qos->latency_tolerance_req) {
struct dev_pm_qos_request *req;

if (val < 0) {
--
2.41.0