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>

3 files changed, 20 insertions, 42 deletions

diff --git a/drivers/pcmcia/ds.c b/drivers/pcmcia/ds.c
index 4014cf8e4a26..92a5af8aa0b4 100644
--- a/drivers/pcmcia/ds.c
+++ b/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 */
diff --git a/include/pcmcia/ds.h b/include/pcmcia/ds.h
index d57847f2f6c1..aab3c13dc310 100644
--- a/include/pcmcia/ds.h
+++ b/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;
diff --git a/include/pcmcia/ss.h b/include/pcmcia/ss.h
index 2e488b60bc76..344705cb42f4 100644
--- a/include/pcmcia/ss.h
+++ b/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;