On 09/05/14 15:56, Douglas Gilbert wrote:
With scsi-mq I think many LLDs probably have a new race possibility between a surprise rmmod of the LLD and another thread presenting a new command at about the same time (or another thread's command completing around that time). Does anything above the LLD stop this happening? Looking at mpt3sas and hpsa module exit calls, they don't seem to guard against this possibility. The test is pretty easy: build the LLD as a module, load it and fire up a multi-thread, libaio fio test on one or more devices (SSDs would probably be good) on that LLD. While the test is running, do 'rmmod LLD'.
An LLD must call scsi_remove_host() directly or indirectly from the module cleanup path. scsi_remove_host() triggers a call to blk_cleanup_queue(). That last function sets the flag QUEUE_FLAG_DYING which prevents that new I/O is queued and waits until previously queued requests have finished before returning.
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