Lun unlink from configFS for Loopback after TMR execution hangs forever

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Hi,

I am testing with Loopback and found, that after a
Loopback LUN has executed a TMR, I can no longer unlink
the LUN.

The rm command hangs in transport_clear_lun_ref() at
wait_for_completion(&lun->lun_shutdown_comp)

The reason is, that transport_lun_remove_cmd() is not
called at the end of target_tmr_work().

It seems, that in other fabrics this call happens implicitly
when the fabric driver calls transport_generic_free_cmd()
during its ->queue_tm_rsp().

Unfortunately the Loopback seems to not comply to the common
way of calling transport_generic_free_cmd() from ->queue_*(),
but calls it from its ->check_stop_free() only.

But the ->check_stop_free() is called by
transport_cmd_check_stop_to_fabric() after it has reset the
se_cmd->se_lun pointer.
Therefore the following transport_generic_free_cmd() skips the
transport_lun_remove_cmd().

So it seems, that Loopback driver is doing wrong.

OTOH, target_tmr_work() seems to be the only place, where
transport_cmd_check_stop_to_fabric() is called without
calling transport_lun_remove_cmd() before.

Now I'm wondering, how to fix the problem:
1) Just (re-)add a call to transport_lun_remove_cmd() before
   calling transport_cmd_check_stop_to_fabric() in
   target_tmr_work()
2) Change Loopback driver to comply with the usual way
   of using transport_generic_free_cmd()

I think I'd prefer 1 and already tested it, works fine for
Loopback. Currently I'm not able to test other fabrics, but
AFAICS the change should not harm other fabric drivers,
because transport_lun_remove_cmd() uses a bit to make safe,
that lun_ref is dropped only once.
Additionally, before commit 2c9fa49e100f "scsi: target/core:
 Make ABORT and LUN RESET handling synchronous" the code
contained the transport_lun_remove_cmd() call.

Regards,
Bodo



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