xe, and shared helpers it uses such as drm_gpuvm, already take bare drm_device references (drm_dev_get()) from several contexts, for example GuC submission fence workers, EU stall, OA and PMU sampling code, and drm_gpuvm's own vm object lifetime, without pairing them with a module reference. Since xe_exit() is only invoked after the module's own refcount has dropped to zero, none of these references currently prevent `rmmod xe` from proceeding while they, or the underlying xe_device release path they can trigger, are still outstanding, i.e. driver code belonging to a module whose text is being freed could still end up executing.
Close this gap by keeping a device-count and waiting for it to reach zero at module unload, then waiting for any release callback that has started executing to finish, using the drm_dev_release_barrier() infrastructure introduced in the previous commit. The wait for the device-count to reach zero at module unload is unbounded and non-interruptible. Rather than blocking silently forever if a reference is ever leaked, use wait_var_event_timeout() with a 20s timeout, well above the typical maximum dma_fence signalling time, and warn once if devices still remain by then, before falling back to an unbounded wait_var_event() so a stuck rmmod is at least observable instead of an indefinite, silent hang. Note that if a reference genuinely leaks, this still ends up as an indefinite uninterruptible sleep, which may eventually trip the kernel's hung-task watchdog. The alternative would be for these bare drm_device references to also take a module reference, which would instead make the module unable to be unloaded unless all its devices are manually unbound first. The wait-based approach is chosen here since it keeps rmmod usable in the common case. drm_dev_release_barrier() uses a single, global SRCU domain shared by all drivers, so xe's wait for its own release callbacks may occasionally end up blocking on an unrelated driver's release path too, a trade-off accepted in favor of not requiring each driver to set up and tear down its own SRCU domain. xe_device_exit() is added as a new module exit hook. Its entry in the init_funcs[] table is placed between xe_destroy_wq_module_init and xe_register_pci_driver, so that (exit functions run in reverse array order) it executes after xe_unregister_pci_driver() has forced all devices to unbind, but before xe_destroy_wq_module_exit() tears down the module-lifetime xe_destroy_wq. This preserves xe_destroy_wq's existing teardown ordering relative to xe_sched_job_module_exit() and xe_hw_fence_module_exit(), which destroy kmem_caches that work drained from xe_destroy_wq relies on, while ensuring xe_destroy_wq itself is only torn down once xe_device_exit() has confirmed no more work can be queued onto it. v2: - Updated commit message to describe the actual implementation (a single 20s wait_var_event_timeout() followed by one pr_warn() and an unbounded wait_var_event(), rather than a loop retrying with a diagnostic every 10s) and its uninterruptible-sleep tradeoff (sashiko) v3: - drm_dev_release_barrier() no longer takes a &drm_driver argument since it now uses a single, global SRCU domain; drop the &drm_driver.release_srcu registration on both xe drm_driver instances accordingly (Christian König) Signed-off-by: Thomas Hellström <[email protected]> Assisted-by: LLM Reviewed-by: Matthew Brost <[email protected]> --- drivers/gpu/drm/xe/xe_device.c | 32 ++++++++++++++++++++++++++++++++ drivers/gpu/drm/xe/xe_device.h | 2 ++ drivers/gpu/drm/xe/xe_module.c | 18 +++++++++++++++++- 3 files changed, 51 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c index 205cb4e7f9e8..c54d734bd890 100644 --- a/drivers/gpu/drm/xe/xe_device.c +++ b/drivers/gpu/drm/xe/xe_device.c @@ -372,6 +372,9 @@ bool xe_device_is_admin_only(const struct xe_device *xe) } #endif +/* Number of allocated struct xe_device */ +static atomic_t xe_device_count; + static void xe_device_destroy(struct drm_device *dev, void *dummy) { struct xe_device *xe = to_xe_device(dev); @@ -391,6 +394,9 @@ static void xe_device_destroy(struct drm_device *dev, void *dummy) destroy_workqueue(xe->destroy_wq); ttm_device_fini(&xe->ttm); + + if (atomic_dec_and_test(&xe_device_count)) + wake_up_var(&xe_device_count); } /** @@ -461,6 +467,7 @@ int xe_device_init_early(struct xe_device *xe) return err; xe_bo_dev_init(&xe->bo_device); + atomic_inc(&xe_device_count); err = drmm_add_action_or_reset(&xe->drm, xe_device_destroy, NULL); if (err) return err; @@ -1501,3 +1508,28 @@ struct xe_vm *xe_device_asid_to_vm(struct xe_device *xe, u32 asid) return vm; } + +/** + * xe_device_exit() - Device subsystem exit function. + * + * Exit function to be called at module unload time. + */ +void xe_device_exit(void) +{ + /* + * Wait for all devices to be freed. 20s is well above the typical + * maximum dma_fence signalling time, so warn and keep waiting if + * we're still not done by then, since it may indicate a leaked + * xe_device reference is stalling module unload. + */ + if (!wait_var_event_timeout(&xe_device_count, + !atomic_read(&xe_device_count), + HZ * 20)) { + pr_warn("%s: Waiting for %d xe device(s) to be freed before unloading.\n", + DRIVER_NAME, atomic_read(&xe_device_count)); + wait_var_event(&xe_device_count, !atomic_read(&xe_device_count)); + } + + /* Wait for any driver release callbacks to complete */ + drm_dev_release_barrier(); +} diff --git a/drivers/gpu/drm/xe/xe_device.h b/drivers/gpu/drm/xe/xe_device.h index 6d3d6d5eba29..83d6dafab53c 100644 --- a/drivers/gpu/drm/xe/xe_device.h +++ b/drivers/gpu/drm/xe/xe_device.h @@ -283,6 +283,8 @@ static inline bool xe_device_is_admin_only(const struct xe_device *xe) } #endif +void xe_device_exit(void); + /* * Occasionally it is seen that the G2H worker starts running after a delay of more than * a second even after being queued and activated by the Linux workqueue subsystem. This diff --git a/drivers/gpu/drm/xe/xe_module.c b/drivers/gpu/drm/xe/xe_module.c index 4bc28dfc1992..c61bd33546f2 100644 --- a/drivers/gpu/drm/xe/xe_module.c +++ b/drivers/gpu/drm/xe/xe_module.c @@ -12,7 +12,7 @@ #include <drm/drm_module.h> #include "xe_defaults.h" -#include "xe_device_types.h" +#include "xe_device.h" #include "xe_drv.h" #include "xe_configfs.h" #include "xe_hw_fence.h" @@ -162,6 +162,22 @@ static const struct init_funcs init_funcs[] = { .init = xe_destroy_wq_module_init, .exit = xe_destroy_wq_module_exit, }, + /* + * xe_destroy_wq_module_exit() must run after xe_device_exit() + * (below), since freeing a device can still queue work on + * xe_destroy_wq that must be drained before the module can safely + * unload. At the same time, xe_device_exit() must run after + * xe_unregister_pci_driver() (below), and xe_destroy_wq_module_exit() + * must run before xe_sched_job_module_exit() and + * xe_hw_fence_module_exit() (above), whose kmem_caches are still used + * by work drained from xe_destroy_wq. Exit functions run in reverse + * array order, so this entry must sit between the + * xe_destroy_wq_module_init entry above and the xe_register_pci_driver + * entry below. + */ + { + .exit = xe_device_exit, + }, { .init = xe_register_pci_driver, .exit = xe_unregister_pci_driver, -- 2.55.0
