[RFC PATCH 2/4] wifi: iwlwifi: use device_schedule_reprobe()

[Daniel Golle]

iwl_trans_schedule_reprobe() open-codes a deferred re-probe: it takes
a module reference, allocates a work item, and the work function calls
device_reprobe() and then ends with put_device(); kfree();
module_put(THIS_MODULE); in module text. That final module_put() is
racy: once the reference count is decremented a concurrent rmmod can
free the module text before the work function's epilogue has finished
executing. The work also does not synchronize against shutdown or
unbind, so a stale re-probe could undo an administrative unbind or
detach a device whose ->shutdown() callback has already run.

Convert to the new device_schedule_reprobe() helper, whose work
function is builtin text and which skips the re-probe when the device
was removed, shutdown reached it, or it is no longer bound to the
driver that scheduled the re-probe. Both call sites keep their delays
(IWL_TRANS_TOP_FOLLOWER_WAIT for the TOP follower case, 0 for the
escalated firmware error case).

Behavioral changes:

- A pending re-probe no longer pins the module: rmmod with a re-probe
  pending now succeeds immediately and the re-probe becomes a no-op,
  instead of rmmod failing with EBUSY. The "Module is being unloaded -
  abort" path disappears together with the try_module_get().

- A re-probe scheduled before a system shutdown or before an
  administrative unbind no longer detaches and rebinds the device
  afterwards.

Signed-off-by: Daniel Golle <daniel@xxxxxxxxxxxxxx>
---
 .../net/wireless/intel/iwlwifi/iwl-trans.c    | 40 +------------------
 1 file changed, 2 insertions(+), 38 deletions(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-trans.c b/drivers/net/wireless/intel/iwlwifi/iwl-trans.c
index 73aae1125042..5ae734cb9027 100644
--- a/drivers/net/wireless/intel/iwlwifi/iwl-trans.c
+++ b/drivers/net/wireless/intel/iwlwifi/iwl-trans.c
@@ -78,47 +78,11 @@ void iwl_trans_free_restart_list(void)
 	}
 }
 
-struct iwl_trans_reprobe {
-	struct device *dev;
-	struct delayed_work work;
-};
-
-static void iwl_trans_reprobe_wk(struct work_struct *wk)
-{
-	struct iwl_trans_reprobe *reprobe;
-
-	reprobe = container_of(wk, typeof(*reprobe), work.work);
-
-	if (device_reprobe(reprobe->dev))
-		dev_err(reprobe->dev, "reprobe failed!\n");
-	put_device(reprobe->dev);
-	kfree(reprobe);
-	module_put(THIS_MODULE);
-}
-
 static void iwl_trans_schedule_reprobe(struct iwl_trans *trans,
 				       unsigned int delay_ms)
 {
-	struct iwl_trans_reprobe *reprobe;
-
-	/*
-	 * get a module reference to avoid doing this while unloading
-	 * anyway and to avoid scheduling a work with code that's
-	 * being removed.
-	 */
-	if (!try_module_get(THIS_MODULE)) {
-		IWL_ERR(trans, "Module is being unloaded - abort\n");
-		return;
-	}
-
-	reprobe = kzalloc_obj(*reprobe);
-	if (!reprobe) {
-		module_put(THIS_MODULE);
-		return;
-	}
-	reprobe->dev = get_device(trans->dev);
-	INIT_DELAYED_WORK(&reprobe->work, iwl_trans_reprobe_wk);
-	schedule_delayed_work(&reprobe->work, msecs_to_jiffies(delay_ms));
+	if (device_schedule_reprobe(trans->dev, delay_ms))
+		IWL_ERR(trans, "Could not schedule reprobe\n");
 }
 
 #define IWL_TRANS_RESET_OK_TIME	7 /* seconds */
-- 
2.55.0