linux-kernel - Re: [PATCH] PM / wakeup: Register wakeup class kobj after device is added

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Message-ID: <CANA+-vB2_pYhYq5cmpyhiwJR3TuO+-2iBPehSXSjun-HN2wb5A@mail.gmail.com>
Date:   Fri, 16 Aug 2019 14:27:35 -0700
From:   Tri Vo <trong@...roid.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>, Qian Cai <cai@....pw>
Subject: Re: [PATCH] PM / wakeup: Register wakeup class kobj after device is added

On Fri, Aug 16, 2019 at 7:56 AM Stephen Boyd <swboyd@...omium.org> wrote:
>
> The device_set_wakeup_enable() function can be called on a device that
> hasn't been registered with device_add() yet. This allows the device to
> be in a state where wakeup is enabled for it but the device isn't
> published to userspace in sysfs yet.
>
> After commit 986845e747af ("PM / wakeup: Show wakeup sources stats in
> sysfs"), calling device_set_wakeup_enable() will fail for a device that
> hasn't been registered with the driver core via device_add(). This is
> because we try to create sysfs entries for the device and associate a
> wakeup class kobject with it before the device has been registered.
> Let's follow a similar approach that device_set_wakeup_capable() takes
> here and register the wakeup class either from
> device_set_wakeup_enable() when the device is already registered, or
> from dpm_sysfs_add() when the device is being registered with the driver
> core via device_add().
>
> Fixes: 986845e747af ("PM / wakeup: Show wakeup sources stats in sysfs")
> Reported-by: Qian Cai <cai@....pw>
> Cc: Qian Cai <cai@....pw>
> Cc: Tri Vo <trong@...roid.com>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
>  drivers/base/power/sysfs.c  | 10 +++++++++-
>  drivers/base/power/wakeup.c | 10 ++++++----
>  2 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
> index 1b9c281cbe41..27ee00f50bd7 100644
> --- a/drivers/base/power/sysfs.c
> +++ b/drivers/base/power/sysfs.c
> @@ -5,6 +5,7 @@
>  #include <linux/export.h>
>  #include <linux/pm_qos.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/pm_wakeup.h>
>  #include <linux/atomic.h>
>  #include <linux/jiffies.h>
>  #include "power.h"
> @@ -661,14 +662,21 @@ int dpm_sysfs_add(struct device *dev)
>                 if (rc)
>                         goto err_runtime;
>         }
> +       if (dev->power.wakeup) {

This conditional checks for the situation when wakeup source
registration have been previously attempted, but failed at
wakeup_source_sysfs_add(). My concern is that it's not easy to
understand what this check does without knowing exactly what
device_wakeup_enable() does to dev->power.wakeup before we reach this
point.

> +               rc = wakeup_source_sysfs_add(dev, dev->power.wakeup);
> +               if (rc)
> +                       goto err_wakeup;
> +       }
>         if (dev->power.set_latency_tolerance) {
>                 rc = sysfs_merge_group(&dev->kobj,
>                                        &pm_qos_latency_tolerance_attr_group);
>                 if (rc)
> -                       goto err_wakeup;
> +                       goto err_wakeup_source;
>         }
>         return 0;
>
> + err_wakeup_source:
> +       wakeup_source_sysfs_remove(dev->power.wakeup);
>   err_wakeup:
>         sysfs_unmerge_group(&dev->kobj, &pm_wakeup_attr_group);
>   err_runtime:
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index f7925820b5ca..5817b51d2b15 100644
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -220,10 +220,12 @@ struct wakeup_source *wakeup_source_register(struct device *dev,
>
>         ws = wakeup_source_create(name);
>         if (ws) {
> -               ret = wakeup_source_sysfs_add(dev, ws);
> -               if (ret) {
> -                       wakeup_source_free(ws);
> -                       return NULL;
> +               if (!dev || device_is_registered(dev)) {

Is there a possible race condition here? If dev->power.wakeup check in
dpm_sysfs_add() is done at the same time as device_is_registered(dev)
check here, then wakeup_source_sysfs_add() won't ever be called?

> +                       ret = wakeup_source_sysfs_add(dev, ws);
> +                       if (ret) {
> +                               wakeup_source_free(ws);
> +                               return NULL;
> +                       }
>                 }
>                 wakeup_source_add(ws);
>         }
> --
> Sent by a computer through tubes
>