[PATCH] fix AB-BA deadlock inversion at cs46xx_dsp_remove_scb

There is a code sequence where the locking is substream->self_group.lock
-> ins->scbs[index].lock

substream->self_group.lock is interrupt safe, and taken from irq context
as well (trace is snipped for brevity)

so what can happen is

cpu 0 cpu 1
user context user context

take ins->scbs[index].lock without disabling interrupts

get substream->self_group.lock (irqsafe)
try to get ins->scbs[index].lock (spins)

interrupt happens
try to get substream->self_group.lock (spins)

which is an obvious AB-BA deadlock

fix is to just take the lock with _irqsafe

Signed-off-by: Arjan van de Ven <[e-mail]>
Cc: Jaroslav Kysela <[e-mail]>
Acked-by: Takashi Iwai <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

sound/pci/cs46xx/dsp_spos_scb_lib.c

···
 void cs46xx_dsp_remove_scb (struct snd_cs46xx *chip, struct dsp_scb_descriptor * scb)
 {
 	struct dsp_spos_instance * ins = chip->dsp_spos_instance;
+	unsigned long flags;
 
 	/* check integrety */
 	snd_assert ( (scb->index >= 0 && 
···
 		     goto _end);
 #endif
 
-	spin_lock(&scb->lock);
+	spin_lock_irqsave(&scb->lock, flags);
 	_dsp_unlink_scb (chip,scb);
-	spin_unlock(&scb->lock);
+	spin_unlock_irqrestore(&scb->lock, flags);
 
 	cs46xx_dsp_proc_free_scb_desc(scb);
 	snd_assert (scb->scb_symbol != NULL, return );