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SubjectRe: [PATCH] PM: Prevent waiting forever on asynchronous resume after abort
On Wed, 1 Sep 2010, Colin Cross wrote:

> Only wait on a parent device during resume if the parent device is
> suspended.
>
> Consider three drivers, A, B, and C. The parent of A is C, and C
> has async_suspend set. On boot, C->power.completion is initialized
> to 0.
>
> During the first suspend:
> suspend_devices_and_enter(...)
> dpm_resume(...)
> device_suspend(A)
> device_suspend(B) returns error, aborts suspend
> dpm_resume_end(...)
> dpm_resume(...)
> device_resume(A)
> dpm_wait(A->parent == C)
> wait_for_completion(C->power.completion)
>
> The wait_for_completion will never complete, because
> complete_all(C->power.completion) will only be called from
> device_suspend(C) or device_resume(C), neither of which is called
> if suspend is aborted before C.

This would work okay if C->power.completion had been initialized to the
completed state during boot, right?

> After a successful suspend->resume cycle, where B doesn't abort
> suspend, C->power.completion is left in the completed state by the
> call to device_resume(C), and the same call path will work if B
> aborts suspend.
>
> Signed-off-by: Colin Cross <ccross@android.com>
> ---
> drivers/base/power/main.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index cb784a0..e159910 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -526,7 +526,8 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
> TRACE_DEVICE(dev);
> TRACE_RESUME(0);
>
> - dpm_wait(dev->parent, async);
> + if (dev->parent && dev->parent->power.status >= DPM_OFF)
> + dpm_wait(dev->parent, async);
> device_lock(dev);
>
> dev->power.status = DPM_RESUMING;

I think it would be better to change device_pm_init() and add a
complete_all().

Alan Stern



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