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Message-ID: <Yr6xYX1vyIS3pQiX@kroah.com>
Date: Fri, 1 Jul 2022 10:33:37 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Ulf Hansson <ulf.hansson@...aro.org>,
Peter Wang <peter.wang@...iatek.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Saravana Kannan <saravanak@...gle.com>
Subject: Re: [PATCH] PM: runtime: Fix supplier device management during
consumer probe
On Thu, Jun 30, 2022 at 09:16:41PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Because pm_runtime_get_suppliers() bumps up the rpm_active counter
> of each device link to a supplier of the given device in addition
> to bumping up the supplier's PM-runtime usage counter, a runtime
> suspend of the consumer device may case the latter to go down to 0
> when pm_runtime_put_suppliers() is running on a remote CPU. If that
> happens after pm_runtime_put_suppliers() has released power.lock for
> the consumer device, and a runtime resume of that device takes place
> immediately after it, before pm_runtime_put() is called for the
> supplier, that pm_runtime_put() call may cause the supplier to be
> suspended even though the consumer is active.
>
> To prevent that from happening, modify pm_runtime_get_suppliers() to
> call pm_runtime_get_sync() for the given device's suppliers without
> touching the rpm_active counters of the involved device links
> Accordingly, modify pm_runtime_put_suppliers() to call pm_runtime_put()
> for the given device's suppliers without looking at the rpm_active
> counters of the device links at hand. [This is analogous to what
> happened before commit 4c06c4e6cf63 ("driver core: Fix possible
> supplier PM-usage counter imbalance").]
>
> Since pm_runtime_get_suppliers() sets supplier_preactivated for each
> device link where the supplier's PM-runtime usage counter has been
> incremented and pm_runtime_put_suppliers() calls pm_runtime_put() for
> the suppliers whose device links have supplier_preactivated set, the
> PM-runtime usage counter is balanced for each supplier and this is
> independent of the runtime suspend and resume of the consumer device.
>
> However, in case a device link with DL_FLAG_PM_RUNTIME set is dropped
> during the consumer device probe, so pm_runtime_get_suppliers() bumps
> up the supplier's PM-runtime usage counter, but it cannot be dropped by
> pm_runtime_put_suppliers(), make device_link_release_fn() take care of
> that.
>
> Fixes: 4c06c4e6cf63 ("driver core: Fix possible supplier PM-usage counter imbalance")
> Reported-by: Peter Wang <peter.wang@...iatek.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> drivers/base/core.c | 10 ++++++++++
> drivers/base/power/runtime.c | 14 +-------------
> 2 files changed, 11 insertions(+), 13 deletions(-)
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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