linux-kernel - Re: [PATCH] PM / runtime: Drop usage count for suppliers at device link removal

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Date:   Sun, 27 May 2018 12:18:05 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Todor Tomov <todor.tomov@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Jon Hunter <jonathanh@...dia.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] PM / runtime: Drop usage count for suppliers at device
 link removal

On Thu, May 24, 2018 at 10:33 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> In the case consumer device is runtime resumed, while the link to the
> supplier is removed, the earlier call to pm_runtime_get_sync() made from
> rpm_get_suppliers() does not get properly balanced with a corresponding
> call to pm_runtime_put(). This leads to that suppliers remains to be
> runtime resumed forever, while they don't need to.
>
> Let's fix the behaviour by calling rpm_put_suppliers() when dropping a
> device link. Not that, since rpm_put_suppliers() checks the
> link->rpm_active flag, we can correctly avoid to call pm_runtime_put() in
> cases when we shouldn't.
>
> Reported-by: Todor Tomov <todor.tomov@...aro.org>
> Fixes: 21d5c57b3726 ("PM / runtime: Use device links")
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> ---
>
> Rafael, I am not sure if this is safe from locking point of view. The device
> link write lock has been taken when pm_runtime_drop_link() is called, hence I
> assume calling rpm_put_suppliers() should be fine!? If not, can you please
> advise how to change?

Holding the lock should be sufficient for the list to be stable, so
AFAICS it is OK.

Thanks,
Rafael