[PATCH 08/13] PM / QoS: Fix constraints alloc vs reclaim locking

[Rob Clark <robdclark@gmail.com>]

From: Rob Clark <robdclark@chromium.org>

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.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/base/power/qos.c | 60 +++++++++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 19 deletions(-)

diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
index 8e93167f1783..f3e0c6b65635 100644
--- a/drivers/base/power/qos.c
+++ b/drivers/base/power/qos.c
@@ -185,18 +185,24 @@ static int apply_constraint(struct dev_pm_qos_request *req,
 }
 
 /*
- * dev_pm_qos_constraints_allocate
+ * dev_pm_qos_constraints_ensure_allocated
  * @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 ensure that devices qos is allocated, before acquiring
+ * dev_pm_qos_mtx.
  */
-static int dev_pm_qos_constraints_allocate(struct device *dev)
+static int dev_pm_qos_constraints_ensure_allocated(struct device *dev)
 {
 	struct dev_pm_qos *qos;
 	struct pm_qos_constraints *c;
 	struct blocking_notifier_head *n;
 
+	if (!dev)
+		return -ENODEV;
+
+	if (!IS_ERR_OR_NULL(dev->power.qos))
+		return 0;
+
 	qos = kzalloc(sizeof(*qos), GFP_KERNEL);
 	if (!qos)
 		return -ENOMEM;
@@ -227,10 +233,26 @@ static int dev_pm_qos_constraints_allocate(struct device *dev)
 
 	INIT_LIST_HEAD(&qos->flags.list);
 
+	mutex_lock(&dev_pm_qos_mtx);
+
+	if (!IS_ERR_OR_NULL(dev->power.qos)) {
+		/*
+		 * We have raced with another task to create the qos.
+		 * No biggie, just free the resources we've allocated
+		 * outside of dev_pm_qos_mtx and move on with life.
+		 */
+		kfree(n);
+		kfree(qos);
+		goto unlock;
+	}
+
 	spin_lock_irq(&dev->power.lock);
 	dev->power.qos = qos;
 	spin_unlock_irq(&dev->power.lock);
 
+unlock:
+	mutex_unlock(&dev_pm_qos_mtx);
+
 	return 0;
 }
 
@@ -331,17 +353,15 @@ static int __dev_pm_qos_add_request(struct device *dev,
 {
 	int ret = 0;
 
-	if (!dev || !req || dev_pm_qos_invalid_req_type(dev, type))
+	if (!req || dev_pm_qos_invalid_req_type(dev, type))
 		return -EINVAL;
 
 	if (WARN(dev_pm_qos_request_active(req),
 		 "%s() called for already added request\n", __func__))
 		return -EINVAL;
 
-	if (IS_ERR(dev->power.qos))
+	if (IS_ERR_OR_NULL(dev->power.qos))
 		ret = -ENODEV;
-	else if (!dev->power.qos)
-		ret = dev_pm_qos_constraints_allocate(dev);
 
 	trace_dev_pm_qos_add_request(dev_name(dev), type, value);
 	if (ret)
@@ -390,6 +410,10 @@ int dev_pm_qos_add_request(struct device *dev, struct dev_pm_qos_request *req,
 {
 	int ret;
 
+	ret = dev_pm_qos_constraints_ensure_allocated(dev);
+	if (ret)
+		return ret;
+
 	mutex_lock(&dev_pm_qos_mtx);
 	ret = __dev_pm_qos_add_request(dev, req, type, value);
 	mutex_unlock(&dev_pm_qos_mtx);
@@ -537,15 +561,11 @@ int dev_pm_qos_add_notifier(struct device *dev, struct notifier_block *notifier,
 {
 	int ret = 0;
 
-	mutex_lock(&dev_pm_qos_mtx);
-
-	if (IS_ERR(dev->power.qos))
-		ret = -ENODEV;
-	else if (!dev->power.qos)
-		ret = dev_pm_qos_constraints_allocate(dev);
-
+	ret = dev_pm_qos_constraints_ensure_allocated(dev);
 	if (ret)
-		goto unlock;
+		return ret;
+
+	mutex_lock(&dev_pm_qos_mtx);
 
 	switch (type) {
 	case DEV_PM_QOS_RESUME_LATENCY:
@@ -565,7 +585,6 @@ int dev_pm_qos_add_notifier(struct device *dev, struct notifier_block *notifier,
 		ret = -EINVAL;
 	}
 
-unlock:
 	mutex_unlock(&dev_pm_qos_mtx);
 	return ret;
 }
@@ -905,10 +924,13 @@ int dev_pm_qos_update_user_latency_tolerance(struct device *dev, s32 val)
 {
 	int ret;
 
+	ret = dev_pm_qos_constraints_ensure_allocated(dev);
+	if (ret)
+		return ret;
+
 	mutex_lock(&dev_pm_qos_mtx);
 
-	if (IS_ERR_OR_NULL(dev->power.qos)
-	    || !dev->power.qos->latency_tolerance_req) {
+	if (!dev->power.qos->latency_tolerance_req) {
 		struct dev_pm_qos_request *req;
 
 		if (val < 0) {
-- 
2.39.2