[PATCH 5.6 069/126] scsi: target: Put lun_ref at end of tmr processing

[Greg Kroah-Hartman]

From: Bodo Stroesser <bstroesser@xxxxxxxxxxxxxx>

commit f2e6b75f6ee82308ef7b00f29e71e5f1c6b3d52a upstream.

Testing with Loopback I 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 drivers call transport_generic_free_cmd() during their
->queue_tm_rsp().

Unfortunately Loopback seems to not comply to the common way
of calling transport_generic_free_cmd() from ->queue_*().
Instead it calls transport_generic_free_cmd() 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 this patch re-adds the transport_lun_remove_cmd() at the end of
target_tmr_work(), which was removed during commit 2c9fa49e100f ("scsi:
target/core: Make ABORT and LUN RESET handling synchronous").

For fabrics using transport_generic_free_cmd() in the usual way the double
call to transport_lun_remove_cmd() doesn't harm, as
transport_lun_remove_cmd() checks for this situation and does not release
lun_ref twice.

Link: https://lore.kernel.org/r/20200513153443.3554-1-bstroesser@xxxxxxxxxxxxxx
Fixes: 2c9fa49e100f ("scsi: target/core: Make ABORT and LUN RESET handling synchronous")
Cc: stable@xxxxxxxxxxxxxxx
Tested-by: Bryant G. Ly <bryangly@xxxxxxxxx>
Reviewed-by: Bart van Assche <bvanassche@xxxxxxx>
Signed-off-by: Bodo Stroesser <bstroesser@xxxxxxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/target/target_core_transport.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -3349,6 +3349,7 @@ static void target_tmr_work(struct work_
 
 	cmd->se_tfo->queue_tm_rsp(cmd);
 
+	transport_lun_remove_cmd(cmd);
 	transport_cmd_check_stop_to_fabric(cmd);
 	return;