Re: [PATCH 2/2] PM: domain: use per-genpd lockdep class

[Ulf Hansson <ulf.hansson@linaro.org>]

On Fri, 11 Jun 2021 at 12:15, Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> In case of nested genpds it is easy to get the following warning from
> lockdep, because all genpd's mutexes share same locking class. Use the
> per-genpd locking class to stop lockdep from warning about possible
> deadlocks. It is not possible to directly use genpd nested locking, as
> it is not the genpd code calling genpd. There are interim calls to
> regulator core.
>
> [    3.030219] ============================================
> [    3.030220] WARNING: possible recursive locking detected
> [    3.030221] 5.13.0-rc3-00054-gf8f0a2f2b643-dirty #2480 Not tainted
> [    3.030222] --------------------------------------------
> [    3.030223] kworker/u16:0/7 is trying to acquire lock:
> [    3.030224] ffffde0eabd29aa0 (&genpd->mlock){+.+.}-{3:3}, at: genpd_lock_mtx+0x18/0x2c
> [    3.030236]
> [    3.030236] but task is already holding lock:
> [    3.030236] ffffde0eabcfd6d0 (&genpd->mlock){+.+.}-{3:3}, at: genpd_lock_mtx+0x18/0x2c
> [    3.030240]
> [    3.030240] other info that might help us debug this:
> [    3.030240]  Possible unsafe locking scenario:
> [    3.030240]
> [    3.030241]        CPU0
> [    3.030241]        ----
> [    3.030242]   lock(&genpd->mlock);
> [    3.030243]   lock(&genpd->mlock);
> [    3.030244]
> [    3.030244]  *** DEADLOCK ***
> [    3.030244]
> [    3.030244]  May be due to missing lock nesting notation
> [    3.030244]
> [    3.030245] 6 locks held by kworker/u16:0/7:
> [    3.030246]  #0: ffff6cca00010938 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x1f0/0x730
> [    3.030252]  #1: ffff8000100c3db0 (deferred_probe_work){+.+.}-{0:0}, at: process_one_work+0x1f0/0x730
> [    3.030255]  #2: ffff6cca00ce3188 (&dev->mutex){....}-{3:3}, at: __device_attach+0x3c/0x184
> [    3.030260]  #3: ffffde0eabcfd6d0 (&genpd->mlock){+.+.}-{3:3}, at: genpd_lock_mtx+0x18/0x2c
> [    3.030264]  #4: ffff8000100c3968 (regulator_ww_class_acquire){+.+.}-{0:0}, at: regulator_lock_dependent+0x6c/0x1b0
> [    3.030270]  #5: ffff6cca00a59158 (regulator_ww_class_mutex){+.+.}-{3:3}, at: regulator_lock_recursive+0x94/0x1d0
> [    3.030273]
> [    3.030273] stack backtrace:
> [    3.030275] CPU: 6 PID: 7 Comm: kworker/u16:0 Not tainted 5.13.0-rc3-00054-gf8f0a2f2b643-dirty #2480
> [    3.030276] Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
> [    3.030278] Workqueue: events_unbound deferred_probe_work_func
> [    3.030280] Call trace:
> [    3.030281]  dump_backtrace+0x0/0x1a0
> [    3.030284]  show_stack+0x18/0x24
> [    3.030286]  dump_stack+0x108/0x188
> [    3.030289]  __lock_acquire+0xa20/0x1e0c
> [    3.030292]  lock_acquire.part.0+0xc8/0x320
> [    3.030294]  lock_acquire+0x68/0x84
> [    3.030296]  __mutex_lock+0xa0/0x4f0
> [    3.030299]  mutex_lock_nested+0x40/0x50
> [    3.030301]  genpd_lock_mtx+0x18/0x2c
> [    3.030303]  dev_pm_genpd_set_performance_state+0x94/0x1a0
> [    3.030305]  reg_domain_enable+0x28/0x4c
> [    3.030308]  _regulator_do_enable+0x420/0x6b0
> [    3.030310]  _regulator_enable+0x178/0x1f0
> [    3.030312]  regulator_enable+0x3c/0x80

At a closer look, I am pretty sure that it's the wrong code design
that triggers this problem, rather than that we have a real problem in
genpd. To put it simply, the code in genpd isn't designed to work like
this. We will end up in circular looking paths, leading to deadlocks,
sooner or later if we allow the above code path.

To fix it, the regulator here needs to be converted to a proper PM
domain. This PM domain should be assigned as the parent to the one
that is requested to be powered on.

> [    3.030314]  gdsc_toggle_logic+0x30/0x124
> [    3.030317]  gdsc_enable+0x60/0x290
> [    3.030318]  _genpd_power_on+0xc0/0x134
> [    3.030320]  genpd_power_on.part.0+0xa4/0x1f0
> [    3.030322]  __genpd_dev_pm_attach+0xf4/0x1b0
> [    3.030324]  genpd_dev_pm_attach+0x60/0x70
> [    3.030326]  dev_pm_domain_attach+0x54/0x5c
> [    3.030329]  platform_probe+0x50/0xe0
> [    3.030330]  really_probe+0xe4/0x510
> [    3.030332]  driver_probe_device+0x64/0xcc
> [    3.030333]  __device_attach_driver+0xb8/0x114
> [    3.030334]  bus_for_each_drv+0x78/0xd0
> [    3.030337]  __device_attach+0xdc/0x184
> [    3.030338]  device_initial_probe+0x14/0x20
> [    3.030339]  bus_probe_device+0x9c/0xa4
> [    3.030340]  deferred_probe_work_func+0x88/0xc4
> [    3.030342]  process_one_work+0x298/0x730
> [    3.030343]  worker_thread+0x74/0x470
> [    3.030344]  kthread+0x168/0x170
> [    3.030346]  ret_from_fork+0x10/0x34
>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

Kind regards
Uffe

> ---
>  drivers/base/power/domain.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index 74219d032910..bdf439b48763 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -1899,20 +1899,33 @@ static int genpd_set_default_power_state(struct generic_pm_domain *genpd)
>         return 0;
>  }
>
> -static void genpd_lock_init(struct generic_pm_domain *genpd)
> +static int genpd_lock_init(struct generic_pm_domain *genpd)
>  {
>         if (genpd->flags & GENPD_FLAG_IRQ_SAFE) {
>                 spin_lock_init(&genpd->slock);
>                 genpd->lock_ops = &genpd_spin_ops;
>         } else {
> -               mutex_init(&genpd->mlock);
> +               /* Some genpds are static, some are dynamically allocated. To
> +                * make lockdep happy always allocate the key dynamically and
> +                * register it. */
> +               genpd->mlock_key = kzalloc(sizeof(genpd->mlock_key), GFP_KERNEL);
> +               if (!genpd->mlock_key)
> +                       return -ENOMEM;
> +
> +               lockdep_register_key(genpd->mlock_key);
> +
> +               __mutex_init(&genpd->mlock, genpd->name, genpd->mlock_key);
>                 genpd->lock_ops = &genpd_mtx_ops;
>         }
> +
> +       return 0;
>  }
>
>  static void genpd_lock_destroy(struct generic_pm_domain *genpd) {
> -       if (!(genpd->flags & GENPD_FLAG_IRQ_SAFE))
> +       if (!(genpd->flags & GENPD_FLAG_IRQ_SAFE)) {
>                 mutex_destroy(&genpd->mlock);
> +               kfree(genpd->mlock_key);
> +       }
>  }
>
>  /**
> @@ -1935,7 +1948,10 @@ int pm_genpd_init(struct generic_pm_domain *genpd,
>         INIT_LIST_HEAD(&genpd->child_links);
>         INIT_LIST_HEAD(&genpd->dev_list);
>         RAW_INIT_NOTIFIER_HEAD(&genpd->power_notifiers);
> -       genpd_lock_init(genpd);
> +       ret = genpd_lock_init(genpd);
> +       if (ret)
> +               return ret;
> +
>         genpd->gov = gov;
>         INIT_WORK(&genpd->power_off_work, genpd_power_off_work_fn);
>         atomic_set(&genpd->sd_count, 0);
> @@ -2040,7 +2056,6 @@ static int genpd_remove(struct generic_pm_domain *genpd)
>                 free_cpumask_var(genpd->cpus);
>         if (genpd->free_states)
>                 genpd->free_states(genpd->states, genpd->state_count);
> -       genpd_lock_destroy(genpd);
>
>         pr_debug("%s: removed %s\n", __func__, genpd->name);
>
> --
> 2.30.2
>