On Fri, 1 May 2020 at 19:18, yanxiaoyong5@xxxxxxxxx <yanxiaoyong5@xxxxxxxxx> wrote: > > it is a race condition,the situation as follows: > a b > mmc_rescan > mmc_sd_detect > mmc_get_card > __mmc_reclaim_host > card is not present __mmc_reclaim_host > mmc_put_card wait a __mmc_release_host > __mmc_release_host > set b TASK_RUNNING > mmc_sd_remove mmc_sd_remove() calls mmc_remove_card(), which calls device_del() on the corresponding card->dev. That leads to ->remove() callback gets invoked for card->dev (see mmc_blk_remove()), which ideally should clean up everything mmc block device related. In other words, beyond this point there should be no thread/user that can call mmc_hw_reset() (which invokes mmc_sd_hw_reset(). > host->card =NULL > (b starts to run) > mmc_sd_hw_reset > finds host->cards is NULL,then oops So, from the above reasoning I need to ask, have you really seen the NULL pointer exception happening? (then we need to look more closely at mmc_blk_remove()) Or do you think there is a problem from a code-inspection point of view? Kind regards Uffe
