lib: allow idr to be used in irq context

Hi,

This patch allows idr to be used in irq context.

idr_pre_get() is necessary to be called before idr_get_new() is called. No locking is necessary when calling idr_pre_get().

But idr_get_new(), idr_find() and idr_remove() must be serialized with respect to each other.

All of the aforementioned, may end up in alloc_layer() or free_layer() which grabs the idp lock using spin_lock.

If idr_get_new() or idr_remove() is used in IRQ context, then we may get a lockup when idr_pre_get was called in process context and an IRQ interrupted while it held the idp lock.

This patch changes the spin_lock to spin_lock_irqsave, and spin_unlock to spin_unlock_irqrestore, to allow idr_get_new(), idr_find() and idr_remove() to be called from IRQ context, while idr_pre_get() to be called in process context.

@@ -37,27 +37,29 @@
 static struct idr_layer *alloc_layer(struct idr *idp)
 {
 	struct idr_layer *p;
+	unsigned long flags;
 
-	spin_lock(&idp->lock);
+	spin_lock_irqsave(&idp->lock, flags);
 	if ((p = idp->id_free)) {
 		idp->id_free = p->ary[0];
 		idp->id_free_cnt--;
 		p->ary[0] = NULL;
 	}
-	spin_unlock(&idp->lock);
+	spin_unlock_irqrestore(&idp->lock, flags);
 	return(p);
 }
 
 static void free_layer(struct idr *idp, struct idr_layer *p)
 {
+	unsigned long flags;
 	/*
 	 * Depends on the return element being zeroed.
 	 */
-	spin_lock(&idp->lock);
+	spin_lock_irqsave(&idp->lock, flags);
 	p->ary[0] = idp->id_free;
 	idp->id_free = p;
 	idp->id_free_cnt++;
-	spin_unlock(&idp->lock);
+	spin_unlock_irqrestore(&idp->lock, flags);
 }
 
 /**