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

Tri Vo
2019-08-16T21:27:48Z

On Fri, Aug 16, 2019 at 7:56 AM Stephen Boyd <swboyd@chromium.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@lca.pw>
> Cc: Qian Cai <cai@lca.pw>
> Cc: Tri Vo <trong@android.com>
> Signed-off-by: Stephen Boyd <swboyd@chromium.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
>