On Fri, Aug 4, 2023 at 10:38 PM Rob Clark <robdclark@xxxxxxxxx> wrote:
>
> On Fri, Aug 4, 2023 at 12:11 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> >
> > On Fri, Aug 4, 2023 at 8:38 PM Rob Clark <robdclark@xxxxxxxxx> wrote:
> > >
> > > On Fri, Aug 4, 2023 at 10:07 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > > >
> > > > On Fri, Aug 4, 2023 at 12:02 AM Rob Clark <robdclark@xxxxxxxxx> wrote:
> > > > >
> > > > > From: Rob Clark <robdclark@xxxxxxxxxxxx>
> > > > >
> > > > > 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@xxxxxxxxxxxx>
> > > > > ---
> > > > > 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;
> > > > > +
> > > >
> > > > It is a bit unfortunate that the mutex is dropped and then immediately
> > > > re-acquired again. I don't think that this is strictly necessary.
> > >
> > > We could have dev_pm_qos_constraints_ensure_allocated() return with
> > > the lock held in the success case if we had to.. but that seems a bit
> > > funny looking. And the dev_pm_qos_update_user_latency_tolerance()
> > > path would need to shuffle slightly to move the kzalloc out of the
> > > lock.
> >
> > Well, what about something like this (modulo whitespace damage by
> > GMail), attached for completeness:
> >
>
> There is one other path to handle, and some small details,
Yes, this was just an illustration of the approach.
> but I think the approach could work.. let's see..
OK
