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Subject[PATCH 1/2] PM-runtime: Fix __pm_runtime_set_status() race with runtime resume
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Commit 4080ab083000 ("PM-runtime: Take suppliers into account in
__pm_runtime_set_status()") introduced a race condition that may
trigger if __pm_runtime_set_status() is used incorrectly (that is,
if it is called when PM-runtime is enabled for the target device
and working).

In that case, if the original PM-runtime status of the device is
RPM_SUSPENDED, a runtime resume of the device may occur after
__pm_runtime_set_status() has dropped its power.lock spinlock
and before deactivating its suppliers, so the suppliers may be
deactivated while the device is PM-runtime-active which may lead
to functional issues.

To avoid that, modify __pm_runtime_set_status() to check whether
or not PM-runtime is enabled for the device before activating its
suppliers (if the new status is RPM_ACTIVE) and either return an
error if that's the case or increment the device's disable_depth
counter to prevent PM-runtime from being enabled for it while
the remaining part of the function is running (disable_depth is
then decremented on the way out).

Fixes: 4080ab083000 ("PM-runtime: Take suppliers into account in __pm_runtime_set_status()")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/base/power/runtime.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/base/power/runtime.c
===================================================================
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -1129,6 +1129,22 @@ int __pm_runtime_set_status(struct devic
if (status != RPM_ACTIVE && status != RPM_SUSPENDED)
return -EINVAL;

+ spin_lock_irq(&dev->power.lock);
+
+ /*
+ * Prevent PM-runtime from being enabled for the device or return an
+ * error if it is enabled already and working.
+ */
+ if (dev->power.runtime_error || dev->power.disable_depth)
+ dev->power.disable_depth++;
+ else
+ error = -EAGAIN;
+
+ spin_unlock_irq(&dev->power.lock);
+
+ if (error)
+ return error;
+
/*
* If the new status is RPM_ACTIVE, the suppliers can be activated
* upfront regardless of the current status, because next time
@@ -1147,12 +1163,6 @@ int __pm_runtime_set_status(struct devic

spin_lock_irq(&dev->power.lock);

- if (!dev->power.runtime_error && !dev->power.disable_depth) {
- status = dev->power.runtime_status;
- error = -EAGAIN;
- goto out;
- }
-
if (dev->power.runtime_status == status || !parent)
goto out_set;

@@ -1205,6 +1215,8 @@ int __pm_runtime_set_status(struct devic
device_links_read_unlock(idx);
}

+ pm_runtime_enable(dev);
+
return error;
}
EXPORT_SYMBOL_GPL(__pm_runtime_set_status);
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