From fa885b06ec7ee07c2498ad0ce4e0717c3b7dd487 Mon Sep 17 00:00:00 2001 From: Raag Jadav Date: Tue, 27 Feb 2024 11:56:48 +0530 Subject: PCI/PM: Allow runtime PM with no PM callbacks at all Commit c5eb1190074c ("PCI / PM: Allow runtime PM without callback functions") eliminated the need for PM callbacks in pci_pm_runtime_suspend() and pci_pm_runtime_resume(), but didn't do the same for pci_pm_runtime_idle(). Therefore, runtime suspend worked as long as the driver implemented at least one PM callback. But if the driver doesn't implement any PM callbacks at all (driver->pm is NULL), pci_pm_runtime_idle() returned -ENOSYS, which prevented runtime suspend. Modify pci_pm_runtime_idle() to allow PCI device power state transitions without runtime PM callbacks and complete the original intention of commit c5eb1190074c ("PCI / PM: Allow runtime PM without callback functions"). Link: https://lore.kernel.org/r/20240227062648.16579-1-raag.jadav@intel.com Signed-off-by: Raag Jadav [bhelgaas: commit log] Signed-off-by: Bjorn Helgaas Tested-by: Jarkko Nikula Reviewed-by: Andy Shevchenko Reviewed-by: Stanislaw Gruszka Acked-by: Rafael J. Wysocki --- drivers/pci/pci-driver.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'drivers/pci') diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c index 51ec9e7e784f..bb7f6775b350 100644 --- a/drivers/pci/pci-driver.c +++ b/drivers/pci/pci-driver.c @@ -1382,10 +1382,7 @@ static int pci_pm_runtime_idle(struct device *dev) if (!pci_dev->driver) return 0; - if (!pm) - return -ENOSYS; - - if (pm->runtime_idle) + if (pm && pm->runtime_idle) return pm->runtime_idle(dev); return 0; -- cgit v1.2.3 From 9d5286d4e7f68beab450deddbb6a32edd5ecf4bf Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Tue, 5 Mar 2024 11:45:38 +0100 Subject: PCI/PM: Drain runtime-idle callbacks before driver removal A race condition between the .runtime_idle() callback and the .remove() callback in the rtsx_pcr PCI driver leads to a kernel crash due to an unhandled page fault [1]. The problem is that rtsx_pci_runtime_idle() is not expected to be running after pm_runtime_get_sync() has been called, but the latter doesn't really guarantee that. It only guarantees that the suspend and resume callbacks will not be running when it returns. However, if a .runtime_idle() callback is already running when pm_runtime_get_sync() is called, the latter will notice that the runtime PM status of the device is RPM_ACTIVE and it will return right away without waiting for the former to complete. In fact, it cannot wait for .runtime_idle() to complete because it may be called from that callback (it arguably does not make much sense to do that, but it is not strictly prohibited). Thus in general, whoever is providing a .runtime_idle() callback needs to protect it from running in parallel with whatever code runs after pm_runtime_get_sync(). [Note that .runtime_idle() will not start after pm_runtime_get_sync() has returned, but it may continue running then if it has started earlier.] One way to address that race condition is to call pm_runtime_barrier() after pm_runtime_get_sync() (not before it, because a nonzero value of the runtime PM usage counter is necessary to prevent runtime PM callbacks from being invoked) to wait for the .runtime_idle() callback to complete should it be running at that point. A suitable place for doing that is in pci_device_remove() which calls pm_runtime_get_sync() before removing the driver, so it may as well call pm_runtime_barrier() subsequently, which will prevent the race in question from occurring, not just in the rtsx_pcr driver, but in any PCI drivers providing .runtime_idle() callbacks. Link: https://lore.kernel.org/lkml/20240229062201.49500-1-kai.heng.feng@canonical.com/ # [1] Link: https://lore.kernel.org/r/5761426.DvuYhMxLoT@kreacher Reported-by: Kai-Heng Feng Signed-off-by: Rafael J. Wysocki Signed-off-by: Bjorn Helgaas Tested-by: Ricky Wu Acked-by: Kai-Heng Feng Cc: --- drivers/pci/pci-driver.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'drivers/pci') diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c index bb7f6775b350..652506c54a54 100644 --- a/drivers/pci/pci-driver.c +++ b/drivers/pci/pci-driver.c @@ -473,6 +473,13 @@ static void pci_device_remove(struct device *dev) if (drv->remove) { pm_runtime_get_sync(dev); + /* + * If the driver provides a .runtime_idle() callback and it has + * started to run already, it may continue to run in parallel + * with the code below, so wait until all of the runtime PM + * activity has completed. + */ + pm_runtime_barrier(dev); drv->remove(pci_dev); pm_runtime_put_noidle(dev); } -- cgit v1.2.3