memstick: Fix deadlock by moving removing flag earlier

The existing memstick core patch: commit 62c59a8 ("memstick: Skip
allocating card when removing host") sets host->removing in
memstick_remove_host(),but still exists a critical time window where
memstick_check can run after host->eject is set but before removing is set.

In the rtsx_usb_ms driver, the problematic sequence is:

rtsx_usb_ms_drv_remove:          memstick_check:
  host->eject = true
  cancel_work_sync(handle_req)     if(!host->removing)
  ...                              memstick_alloc_card()
                                     memstick_set_rw_addr()
                                       memstick_new_req()
                                         rtsx_usb_ms_request()
                                           if(!host->eject)
                                           skip schedule_work
                                       wait_for_completion()
  memstick_remove_host:                [blocks indefinitely]
    host->removing = true
    flush_workqueue()
    [block]

1. rtsx_usb_ms_drv_remove sets host->eject = true
2. cancel_work_sync(&host->handle_req) runs
3. memstick_check work may be executed here <-- danger window
4. memstick_remove_host sets removing = 1

During this window (step 3), memstick_check calls memstick_alloc_card,
which may indefinitely waiting for mrq_complete completion that will
never occur because rtsx_usb_ms_request sees eject=true and skips
scheduling work, memstick_set_rw_addr waits forever for completion.

This causes a deadlock when memstick_remove_host tries to flush_workqueue,
waiting for memstick_check to complete, while memstick_check is blocked
waiting for mrq_complete completion.

Fix this by setting removing=true at the start of rtsx_usb_ms_drv_remove,
before any work cancellation. This ensures memstick_check will see the
removing flag immediately and exit early, avoiding the deadlock.

Fixes: 62c59a8 ("memstick: Skip allocating card when removing host")
Signed-off-by: Jiayi Li <lijiayi@kylinos.cn>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250804013604.1311218-1-lijiayi@kylinos.cn
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: Jiayi Li

drivers/memstick/core/memstick.c

@@ -555,7 +555,6 @@ EXPORT_SYMBOL(memstick_add_host);
  */
 void memstick_remove_host(struct memstick_host *host)
 {
-	host->removing = 1;
 	flush_workqueue(workqueue);
 	mutex_lock(&host->lock);
 	if (host->card)

drivers/memstick/host/rtsx_usb_ms.c

@@ -812,6 +812,7 @@ static void rtsx_usb_ms_drv_remove(struct platform_device *pdev)
 	int err;
 
 	host->eject = true;
+	msh->removing = true;
 	cancel_work_sync(&host->handle_req);
 	cancel_delayed_work_sync(&host->poll_card);