#include <linux/module.h>
#include <linux/moduleparam.h>
+#include <linux/atomic.h>
#include <linux/bitops.h>
+#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/if_ether.h>
#include <linux/kernel.h>
/* Per-channel lock */
spinlock_t lock;
+ /* Keep track of how many things are using this struct.
+ * Once it reaches 0, we are in the process of cleaning up,
+ * and new operations will be cancelled immediately.
+ * Use atomic_t rather than refcount_t because we deliberately
+ * decrement to 0, and refcount_dec() spills a WARN_ONCE in
+ * that case.
+ */
+ atomic_t refcount;
+
/* TTY TX helpers */
struct work_struct tx_work; /* Flushes TTY TX buffer */
unsigned char txbuf[32];
};
-static DEFINE_SPINLOCK(elmcan_open_lock);
+/* A lock for all tty->disc_data handled by this ldisc.
+ * This is to prevent a case where tty->disc_data is set to NULL,
+ * yet someone is still trying to dereference it.
+ * Without this, we cannot do a clean shutdown.
+ */
+static DEFINE_SPINLOCK(elmcan_discdata_lock);
* (takes elm->lock) *
************************************************************************/
+/*
+ * Get a reference to our struct, taking into account locks/refcounts.
+ * This is to ensure ordering in case we are shutting down, and to ensure
+ * there is a refcount at all (because tty->disc_data may be NULL).
+ */
+static struct elmcan* get_elm(struct tty_struct *tty)
+{
+ struct elmcan *elm;
+ bool got_ref;
+
+ /* Lock all elmcan TTYs, so tty->disc_data can't become NULL
+ * the moment before we increase the reference counter.
+ */
+ spin_lock_bh(&elmcan_discdata_lock);
+ elm = (struct elmcan *) tty->disc_data;
+
+ if (!elm) {
+ spin_unlock_bh(&elmcan_discdata_lock);
+ return NULL;
+ }
+
+ got_ref = atomic_inc_not_zero(&elm->refcount);
+ spin_unlock_bh(&elmcan_discdata_lock);
+
+ if (!got_ref) {
+ return NULL;
+ }
+
+ return elm;
+}
+
+static void put_elm(struct elmcan *elm)
+{
+ atomic_dec(&elm->refcount);
+}
+
+
+
/*
* Handle the 'receiver data ready' interrupt.
* This function is called by the 'tty_io' module in the kernel when
static void elmcan_ldisc_rx(struct tty_struct *tty,
const unsigned char *cp, char *fp, int count)
{
- struct elmcan *elm = (struct elmcan *) tty->disc_data;
+ struct elmcan *elm = get_elm(tty);
if (!elm)
return;
spin_lock_bh(&elm->lock);
elm327_panic(elm);
spin_unlock_bh(&elm->lock);
+
+ put_elm(elm);
return;
}
if (*cp != 0) {
spin_lock_bh(&elm->lock);
elm327_panic(elm);
spin_unlock_bh(&elm->lock);
+
+ put_elm(elm);
return;
}
spin_lock_bh(&elm->lock);
elm327_parse_rxbuf(elm);
spin_unlock_bh(&elm->lock);
+
+ put_elm(elm);
}
/*
*/
static void elmcan_ldisc_tx_worker(struct work_struct *work)
{
+ /* No need to use get_elm() here, as we'll always flush workers
+ * befory destroying the elmcan object.
+ */
struct elmcan *elm = container_of(work, struct elmcan, tx_work);
ssize_t actual;
*/
static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
{
- struct elmcan *elm = tty->disc_data;
+ struct elmcan *elm = get_elm(tty);
+
+ if (!elm)
+ return;
schedule_work(&elm->tx_work);
+
+ put_elm(elm);
}
if (!tty->ops->write)
return -EOPNOTSUPP;
- elm = tty->disc_data;
-
- /* First make sure we're not already connected.
- * Also, protect against simlutaneous open calls. */
- spin_lock_bh(&elmcan_open_lock);
- if (elm) {
- spin_unlock_bh(&elmcan_open_lock);
- return -EEXIST;
- }
- spin_unlock_bh(&elmcan_open_lock);
/* OK. Find a free elmcan channel to use. */
dev = alloc_candev(sizeof(struct elmcan), 0);
tty->receive_room = 65536; /* We don't flow control */
elm->txleft = 0; /* Clear TTY TX buffer */
spin_lock_init(&elm->lock);
+ atomic_set(&elm->refcount, 1);
INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
/* Configure CAN metadata */
*/
static void elmcan_ldisc_close(struct tty_struct *tty)
{
- struct elmcan *elm = (struct elmcan *) tty->disc_data;
+ /* Use get_elm() to synchronize against other users */
+ struct elmcan *elm = get_elm(tty);
- /* First make sure we're connected. */
if (!elm)
return;
- /* Flush network side */
+ /* Tear down network side.
+ * unregister_netdev() calls .ndo_stop() so we don't have to.
+ */
unregister_candev(elm->dev);
+ /* Decrease the refcount twice, once for our own get_elm(),
+ * and once to remove the count of 1 that we set in _open().
+ * Once it reaches 0, we can safely destroy it.
+ */
+ put_elm(elm);
+ put_elm(elm);
+
+ /* Spin until refcount reaches 0 */
+ while(atomic_read(&elm->refcount) > 0)
+ msleep(1);
+
+ /* At this point, all ldisc calls to us will be no-ops.
+ * Since the refcount is 0, they are bailing immediately.
+ */
+
/* Mark channel as dead */
spin_lock_bh(&elm->lock);
tty->disc_data = NULL;
/* Flush TTY side */
flush_work(&elm->tx_work);
+ netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
+
/* Free our memory */
free_candev(elm->dev);
}
static int elmcan_ldisc_ioctl(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg)
{
- struct elmcan *elm = (struct elmcan *) tty->disc_data;
+ struct elmcan *elm = get_elm(tty);
unsigned int tmp;
/* First make sure we're connected. */
switch (cmd) {
case SIOCGIFNAME:
tmp = strlen(elm->ifname) + 1;
- if (copy_to_user((void __user *)arg, elm->ifname, tmp))
+ if (copy_to_user((void __user *)arg, elm->ifname, tmp)) {
+ put_elm(elm);
return -EFAULT;
+ }
+
+ put_elm(elm);
return 0;
case SIOCSIFHWADDR:
+ put_elm(elm);
return -EINVAL;
default:
+ put_elm(elm);
return tty_mode_ioctl(tty, file, cmd, arg);
}
}
projects / elmcan.git / commitdiff