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

Rob Clark
2023-08-23T21:03:10Z

On Tue, Aug 22, 2023 at 11:48 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Tue, Aug 22, 2023 at 8:02 PM Rob Clark <robdclark@gmail.com> wrote:
> >
> > 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
>
> acquiring
>
> > 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>
>
> Please feel free to add
>
> Acked-by: Rafael J. Wysocki <rafael@kernel.org>
>
> to this patch and the next 2 PM QoS ones in this series.

btw, Georgi picked up the interconnect patches. I think it is fine if
you want to pick up the PM patches, as there are no dependencies
between these and other patches in the series. But lmk if you want to
handle it in a different way

BR,
-R

> Thanks!
>
> > ---
> > 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
> >