mtd: maps: pcmciamtd: fix possible sleep-in-atomic-context bugs in pcmciamtd_set_vpp()

The driver may sleep while holding a spinlock.
The function call path (from bottom to top) in Linux 4.19 is:

drivers/pcmcia/pcmcia_resource.c, 312:
	mutex_lock in pcmcia_fixup_vpp
drivers/mtd/maps/pcmciamtd.c, 309:
	pcmcia_fixup_vpp in pcmciamtd_set_vpp
drivers/mtd/maps/pcmciamtd.c, 306:
	_raw_spin_lock_irqsave in pcmciamtd_set_vpp

drivers/pcmcia/pcmcia_resource.c, 312:
	mutex_lock in pcmcia_fixup_vpp
drivers/mtd/maps/pcmciamtd.c, 312:
	pcmcia_fixup_vpp in pcmciamtd_set_vpp
drivers/mtd/maps/pcmciamtd.c, 306:
	_raw_spin_lock_irqsave in pcmciamtd_set_vp

mutex_lock() may sleep at runtime.

To fix these bugs, the spinlock is replaced with a mutex.

These bugs are found by a static analysis tool STCheck written by
myself.
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/maps/pcmciamtd.c

@@ -294,16 +294,15 @@ static void pcmcia_copy_to(struct map_info *map, unsigned long to, const void *f
 }
 
 
-static DEFINE_SPINLOCK(pcmcia_vpp_lock);
+static DEFINE_MUTEX(pcmcia_vpp_lock);
 static int pcmcia_vpp_refcnt;
 static void pcmciamtd_set_vpp(struct map_info *map, int on)
 {
 	struct pcmciamtd_dev *dev = (struct pcmciamtd_dev *)map->map_priv_1;
 	struct pcmcia_device *link = dev->p_dev;
-	unsigned long flags;
 
 	pr_debug("dev = %p on = %d vpp = %d\n\n", dev, on, dev->vpp);
-	spin_lock_irqsave(&pcmcia_vpp_lock, flags);
+	mutex_lock(&pcmcia_vpp_lock);
 	if (on) {
 		if (++pcmcia_vpp_refcnt == 1)   /* first nested 'on' */
 			pcmcia_fixup_vpp(link, dev->vpp);
@@ -311,7 +310,7 @@ static void pcmciamtd_set_vpp(struct map_info *map, int on)
 		if (--pcmcia_vpp_refcnt == 0)   /* last nested 'off' */
 			pcmcia_fixup_vpp(link, 0);
 	}
-	spin_unlock_irqrestore(&pcmcia_vpp_lock, flags);
+	mutex_unlock(&pcmcia_vpp_lock);
 }