net: ethernet: ti: cpdma: fix lockup in cpdma_ctlr_destroy()

Fix deadlock in cpdma_ctlr_destroy() which is triggered now on
cpsw module removal:
 cpsw_remove()
 - cpdma_ctlr_destroy()
   - spin_lock_irqsave(&ctlr->lock, flags)
   - cpdma_ctlr_stop()
     - spin_lock_irqsave(&ctlr->lock, flags);
   - cpdma_chan_destroy()
     - spin_lock_irqsave(&ctlr->lock, flags);

The issue has not been observed before because CPDMA channels have
been destroyed manually by CPSW until commit d941ebe ("net:
ethernet: ti: cpsw: use destroy ctlr to destroy channels") was merged.

Signed-off-by: Grygorii Strashko <[email protected]>
Reviewed-by: Mugunthan V N <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

drivers/net/ethernet/ti/davinci_cpdma.c

@@ -357,21 +357,18 @@ EXPORT_SYMBOL_GPL(cpdma_ctlr_stop);
 
 int cpdma_ctlr_destroy(struct cpdma_ctlr *ctlr)
 {
-	unsigned long flags;
 	int ret = 0, i;
 
 	if (!ctlr)
 		return -EINVAL;
 
-	spin_lock_irqsave(&ctlr->lock, flags);
 	if (ctlr->state != CPDMA_STATE_IDLE)
 		cpdma_ctlr_stop(ctlr);
 
 	for (i = 0; i < ARRAY_SIZE(ctlr->channels); i++)
 		cpdma_chan_destroy(ctlr->channels[i]);
 
 	cpdma_desc_pool_destroy(ctlr->pool);
-	spin_unlock_irqrestore(&ctlr->lock, flags);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(cpdma_ctlr_destroy);