Re: [PATCH v2] target: core: remove from tmr_list at lun unlink

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On 4/16/21 4:38 PM, Mike Christie wrote:
> On 4/16/21 4:21 AM, Dmitry Bogdanov wrote:
>> Currently TMF commands are removed from de_device.dev_tmf_list at
>> the very end of se_cmd lifecycle. But se_lun unlinks from se_cmd
>> up on a command status (response) is queued in transport layer.
>> It means that LUN and backend device can be deleted meantime and at
>> the moment of repsonse completion a panic is occured:
>>
>> target_tmr_work()
>> 	cmd->se_tfo->queue_tm_rsp(cmd); // send abort_rsp to a wire
>> 	transport_lun_remove_cmd(cmd) // unlink se_cmd from se_lun
>> - // - // - // -
>> <<<--- lun remove
>> <<<--- core backend device remove
>> - // - // - // -
>> qlt_handle_abts_completion()
>>   tfo->free_mcmd()
>>     transport_generic_free_cmd()
>>       target_put_sess_cmd()
>>         core_tmr_release_req() {
>>           if (dev) { // backend device, can not be null
>>             spin_lock_irqsave(&dev->se_tmr_lock, flags); //<<<--- CRASH
>>
> 
> Sorry about this. I was thinking about this patch some more while
> reviewing this version.
> 
> Is there another race possible?
> 
> 1. We have a cmd running in lio.
> 2. The initiator times it out and sends tmf.
> 3. cmd completes.
> 4. target_submit_tmr has called transport_lookup_tmr_lun.
> 5. transport_lookup_tmr_lun has set se_dev and tmr_dev.
> 6. You now remove the lun and device.
> 7. Now you crash on the dev references.
> 
> I think we need to do a percpu_ref_tryget_live in transport_lookup_tmr_lun
> like is done in transport_lookup_cmd_lun. If successful set
> 
> se_cmd->lun_ref_active = true;
> 
> If we get the ref, we drop it in transport_lun_remove_cmd like with
> the non tmr case.
> 

Ignore this. I see we do a percpu_ref_tryget_live in there already.





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