Re: [PATCH v4] target: core: remove from tmr_list at lun unlink

[Mike Christie <michael.christie@oracle.com>]

On 10/18/21 8:57 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
> 
> Call Trace:
> NIP [c000000000e1683c] _raw_spin_lock_irqsave+0x2c/0xc0
> LR [c00800000e433338] core_tmr_release_req+0x40/0xa0 [target_core_mod]
> Call Trace:
> (unreliable)
> 0x0
> target_put_sess_cmd+0x2a0/0x370 [target_core_mod]
> transport_generic_free_cmd+0x6c/0x1b0 [target_core_mod]
> tcm_qla2xxx_complete_mcmd+0x28/0x50 [tcm_qla2xxx]
> process_one_work+0x2c4/0x5c0
> worker_thread+0x88/0x690
> 
> For FC protocol it is a race condition, but for iSCSI protocol it is
> easyly reproduced by manual sending iSCSI commands:
> - Send some SCSI sommand
> - Send Abort of that command over iSCSI
> - Remove LUN on target
> - Send next iSCSI command to acknowledge the Abort_Response
> - target panics
> 
> There is no sense to keep the command in tmr_list until response
> completion, so move the removal from tmr_list from the response
> completion to the response queueing when lun is unlinked.
> Move the removal from state list too as it is a subject to the same
> race condition.
> 
> Fixes: c66ac9db8d4a ("[SCSI] target: Add LIO target core v4.0.0-rc6")
> Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
> Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
> 
> ---
> v4:
>  remove superfluous transport_lookup_tmr_lun that could race with lun
> reset
> v3:
>  remove iscsi fix as not related to the issue
>  avoid double removal from tmr_list
> v2:
>  fix stuck in tmr list in error case
> 
> The issue exists from the very begining.
> I uploaded a scapy script that helps to reproduce the issue at
> https://gist.github.com/logost/cb93df41dd2432454324449b390403c4


Reviewed-by: Mike Christie <michael.christie@oracle.com>