[PATCH] PM: runtime: Fix check_flush_dependency warning from pm_runtime_remove

[Zhou Minqiang]

When a WQ_MEM_RECLAIM workqueue (e.g. iscsi_ctrl) triggers device removal
via device_del -> pm_runtime_remove, the unconditional flush_work inside
pm_runtime_remove can trigger a check_flush_dependency warning:

  CPU1: pm_wq worker                 CPU2: iscsi_ctrl wq
  --------                           --------

  pm_runtime_work(starget)           pm_runtime_remove(starget)
    spin_lock_irq(&starget->lock)      __pm_runtime_disable(starget, false)
    request_pending = false              spin_lock_irq(&starget->lock)
                                         (blocked, CPU1 holds the lock)

    rpm_suspend(starget, RPM_NOWAIT)
      status = RPM_SUSPENDING
      rpm_callback(cb, starget)
        spin_unlock_irq(&starget->lock)
                                         (acquires lock)
                                         disable_depth 0→1
                                         __pm_runtime_barrier():
                                           request_pending == false
                                             → skip cancel_work_sync
                                           status == RPM_SUSPENDING
                                             → enter wait_queue, sleep
                                           spin_unlock_irq(&starget->lock)
        cb(starget) → 0
        spin_lock_irq(&starget->lock)
      status = RPM_SUSPENDED
      wake_up_all(&wait_queue)
                                           (woken up, waiting for lock)
      spin_unlock(&starget->lock)          spin_lock_irq(&starget->lock)
                                             status == RPM_SUSPENDED
      spin_lock(&parent->lock)                → exit wait_queue
      rpm_idle(parent, RPM_ASYNC)        barrier returns
      spin_unlock(&parent->lock)       flush_work(&starget->work)
      spin_lock(&starget->lock)          __flush_work(from_cancel=false)
      spin_unlock_irq(&starget->lock)      check_flush_dependency()
                                            ← WARNING!

Replace flush_work with cancel_work_sync in pm_runtime_remove.
cancel_work_sync internally calls __flush_work with from_cancel=true,
which causes check_flush_dependency to return early before the warning.
This preserves the use-after-free fix from commit 29ab76827761
("PM: runtime: Fix a race condition related to device removal")
without the warning.

Fixes: 29ab76827761 ("PM: runtime: Fix a race condition related to device removal")
Signed-off-by: Zhou Minqiang <zhouminqiang2@xxxxxxxxxx>
---
 drivers/base/power/runtime.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 335288e8b5b3..31537b745c81 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -1895,7 +1895,7 @@ void pm_runtime_reinit(struct device *dev)
 void pm_runtime_remove(struct device *dev)
 {
 	__pm_runtime_disable(dev, false);
-	flush_work(&dev->power.work);
+	cancel_work_sync(&dev->power.work);
 	pm_runtime_reinit(dev);
 }
 
-- 
2.52.0