spi: Fix unregistration of controller with fixed SPI bus number

Commit 9b61e30 (spi: Pick spi bus number from Linux idr or spi alias)
ceased to unregister SPI buses with fixed bus numbers. Moreover this is
visible only if CONFIG_SPI_DEBUG=y is set or when trying to re-register
the same SPI controller.

rmmod spi_pxa2xx_platform (with CONFIG_SPI_DEBUG=y):
[   26.788362] spi_master spi1: attempting to delete unregistered controller [spi1]

modprobe spi_pxa2xx_platform:
[   37.883137] sysfs: cannot create duplicate filename '/devices/pci0000:00/0000:00:19.0/pxa2xx-spi.12/spi_master/spi1'
[   37.894984] CPU: 1 PID: 1467 Comm: modprobe Not tainted 4.16.0-rc4+ #21
[   37.902384] Call Trace:
...
[   38.122680] kobject_add_internal failed for spi1 with -EEXIST, don't try to register things with the same name in the same directory.
[   38.136154] WARNING: CPU: 1 PID: 1467 at lib/kobject.c:238 kobject_add_internal+0x2a5/0x2f0
...
[   38.513817] pxa2xx-spi pxa2xx-spi.12: problem registering spi master
[   38.521036] pxa2xx-spi: probe of pxa2xx-spi.12 failed with error -17

Fix this by not returning immediately from spi_unregister_controller() if
idr_find() doesn't find controller with given ID/bus number. It finds
only those controllers that were registered with dynamic SPI bus
numbers. Only conditional cleanup between dynamic and fixed bus numbers
is to remove allocated IDR.

Fixes: 9b61e30 (spi: Pick spi bus number from Linux idr or spi alias)
Cc: stable@vger.kernel.org
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: jhnikula

drivers/spi/spi.c

@@ -2254,12 +2254,6 @@ void spi_unregister_controller(struct spi_controller *ctlr)
 	mutex_lock(&board_lock);
 	found = idr_find(&spi_master_idr, id);
 	mutex_unlock(&board_lock);
-	if (found != ctlr) {
-		dev_dbg(&ctlr->dev,
-			"attempting to delete unregistered controller [%s]\n",
-			dev_name(&ctlr->dev));
-		return;
-	}
 	if (ctlr->queued) {
 		if (spi_destroy_queue(ctlr))
 			dev_err(&ctlr->dev, "queue remove failed\n");
@@ -2272,7 +2266,8 @@ void spi_unregister_controller(struct spi_controller *ctlr)
 	device_unregister(&ctlr->dev);
 	/* free bus id */
 	mutex_lock(&board_lock);
-	idr_remove(&spi_master_idr, id);
+	if (found == ctlr)
+		idr_remove(&spi_master_idr, id);
 	mutex_unlock(&board_lock);
 }
 EXPORT_SYMBOL_GPL(spi_unregister_controller);