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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 4 Aug 2023 22:45:55 +0200
Message-ID: <CAJZ5v0h=cuL7rfEpYeSOySCqA0wrA7XsneZTLCMQxUXjWBgKjg@mail.gmail.com>
Subject: Re: [PATCH v3 3/9] PM / QoS: Fix constraints alloc vs reclaim locking
To:     Rob Clark <robdclark@gmail.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        dri-devel@lists.freedesktop.org, linux-arm-msm@vger.kernel.org,
        freedreno@lists.freedesktop.org,
        Rob Clark <robdclark@chromium.org>,
        Pavel Machek <pavel@ucw.cz>, Len Brown <len.brown@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "open list:HIBERNATION (aka Software Suspend, aka swsusp)" 
        <linux-pm@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Fri, Aug 4, 2023 at 10:38 PM Rob Clark <robdclark@gmail.com> wrote:
>
> On Fri, Aug 4, 2023 at 12:11 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Fri, Aug 4, 2023 at 8:38 PM Rob Clark <robdclark@gmail.com> wrote:
> > >
> > > On Fri, Aug 4, 2023 at 10:07 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > > >
> > > > On Fri, Aug 4, 2023 at 12:02 AM 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
> > > > > 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;
> > > > > +
> > > >
> > > > 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