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

Rob Clark
2023-08-22T19:42:07Z

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.
>

thanks

> 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
> >