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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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