pcmcia: pcmcia_dev_present bugfix

pcmcia_dev_present is in and by itself buggy. Add a note specifying
why it is broken, and replace the broken locking -- taking a mutex
is a bad idea in IRQ context, from which this function is rarely
called -- by an atomic_t.
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

drivers/pcmcia/ds.c

@@ -335,7 +335,6 @@ static void pcmcia_card_remove(struct pcmcia_socket *s, struct pcmcia_device *le
 
 		mutex_lock(&s->ops_mutex);
 		list_del(&p_dev->socket_device_list);
-		p_dev->_removed = 1;
 		mutex_unlock(&s->ops_mutex);
 
 		dev_dbg(&p_dev->dev, "unregistering device\n");
@@ -654,14 +653,7 @@ static int pcmcia_requery_callback(struct device *dev, void * _data)
 
 static void pcmcia_requery(struct pcmcia_socket *s)
 {
-	int present, has_pfc;
-
-	mutex_lock(&s->ops_mutex);
-	present = s->pcmcia_state.present;
-	mutex_unlock(&s->ops_mutex);
-
-	if (!present)
-		return;
+	int has_pfc;
 
 	if (s->functions == 0) {
 		pcmcia_card_add(s);
@@ -1260,9 +1252,7 @@ static int ds_event(struct pcmcia_socket *skt, event_t event, int priority)
 
 	switch (event) {
 	case CS_EVENT_CARD_REMOVAL:
-		mutex_lock(&s->ops_mutex);
-		s->pcmcia_state.present = 0;
-		mutex_unlock(&s->ops_mutex);
+		atomic_set(&skt->present, 0);
 		pcmcia_card_remove(skt, NULL);
 		handle_event(skt, event);
 		mutex_lock(&s->ops_mutex);
@@ -1271,9 +1261,9 @@ static int ds_event(struct pcmcia_socket *skt, event_t event, int priority)
 		break;
 
 	case CS_EVENT_CARD_INSERTION:
+		atomic_set(&skt->present, 1);
 		mutex_lock(&s->ops_mutex);
 		s->pcmcia_state.has_pfc = 0;
-		s->pcmcia_state.present = 1;
 		destroy_cis_cache(s); /* to be on the safe side... */
 		mutex_unlock(&s->ops_mutex);
 		pcmcia_card_add(skt);
@@ -1313,7 +1303,13 @@ static int ds_event(struct pcmcia_socket *skt, event_t event, int priority)
     return 0;
 } /* ds_event */
 
-
+/*
+ * NOTE: This is racy. There's no guarantee the card will still be
+ * physically present, even if the call to this function returns
+ * non-NULL. Furthermore, the device driver most likely is unbound
+ * almost immediately, so the timeframe where pcmcia_dev_present
+ * returns NULL is probably really really small.
+ */
 struct pcmcia_device *pcmcia_dev_present(struct pcmcia_device *_p_dev)
 {
 	struct pcmcia_device *p_dev;
@@ -1323,22 +1319,9 @@ struct pcmcia_device *pcmcia_dev_present(struct pcmcia_device *_p_dev)
 	if (!p_dev)
 		return NULL;
 
-	mutex_lock(&p_dev->socket->ops_mutex);
-	if (!p_dev->socket->pcmcia_state.present)
-		goto out;
+	if (atomic_read(&p_dev->socket->present) != 0)
+		ret = p_dev;
 
-	if (p_dev->socket->pcmcia_state.dead)
-		goto out;
-
-	if (p_dev->_removed)
-		goto out;
-
-	if (p_dev->suspended)
-		goto out;
-
-	ret = p_dev;
- out:
-	mutex_unlock(&p_dev->socket->ops_mutex);
 	pcmcia_put_dev(p_dev);
 	return ret;
 }
@@ -1388,6 +1371,8 @@ static int __devinit pcmcia_bus_add_socket(struct device *dev,
 		return ret;
 	}
 
+	atomic_set(&socket->present, 0);
+
 	return 0;
 }
 
@@ -1399,10 +1384,6 @@ static void pcmcia_bus_remove_socket(struct device *dev,
 	if (!socket)
 		return;
 
-	mutex_lock(&socket->ops_mutex);
-	socket->pcmcia_state.dead = 1;
-	mutex_unlock(&socket->ops_mutex);
-
 	pccard_register_pcmcia(socket, NULL);
 
 	/* unregister any unbound devices */

include/pcmcia/ds.h

@@ -26,6 +26,7 @@
 #ifdef __KERNEL__
 #include <linux/device.h>
 #include <pcmcia/ss.h>
+#include <asm/atomic.h>
 
 /*
  * PCMCIA device drivers (16-bit cards only; 32-bit cards require CardBus
@@ -94,10 +95,8 @@ struct pcmcia_device {
 	config_req_t		conf;
 	window_handle_t		win;
 
-	/* Is the device suspended, or in the process of
-	 * being removed? */
+	/* Is the device suspended? */
 	u16			suspended:1;
-	u16			_removed:1;
 
 	/* Flags whether io, irq, win configurations were
 	 * requested, and whether the configuration is "locked" */
@@ -115,7 +114,7 @@ struct pcmcia_device {
 	u16			has_card_id:1;
 	u16			has_func_id:1;
 
-	u16			reserved:3;
+	u16			reserved:4;
 
 	u8			func_id;
 	u16			manf_id;

include/pcmcia/ss.h

@@ -224,18 +224,16 @@ struct pcmcia_socket {
 
 	/* 16-bit state: */
 	struct {
-		/* PCMCIA card is present in socket */
-		u8			present:1;
 		/* "master" ioctl is used */
 		u8			busy:1;
-		/* pcmcia module is being unloaded */
-		u8			dead:1;
 		/* the PCMCIA card consists of two pseudo devices */
 		u8			has_pfc:1;
 
-		u8			reserved:4;
+		u8			reserved:6;
 	} pcmcia_state;
 
+	/* non-zero if PCMCIA card is present */
+	atomic_t			present;
 
 #ifdef CONFIG_PCMCIA_IOCTL
 	struct user_info_t		*user;