spi: remove some spidev oops-on-rmmod paths

Somehow the spidev code forgot to include a critical mechanism: when the
underlying device is removed (e.g.  spi_master rmmod), open file
descriptors must be prevented from issuing new I/O requests to that
device.  On penalty of the oopsing reported by Sebastian Siewior
<bigeasy@tglx.de> ...

This is a partial fix, adding handshaking between the lower level (SPI
messaging) and the file operations using the spi_dev.  (It also fixes an
issue where reads and writes didn't return the number of bytes sent or
received.)

There's still a refcounting issue to be addressed (separately).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Reported-by: Sebastian Siewior <bigeasy@tglx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 89 insertions, 13 deletions

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index b3518ca9f04e..41620c0fb046 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -68,6 +68,7 @@ static unsigned long	minors[N_SPI_MINORS / BITS_PER_LONG];
 
 struct spidev_data {
         struct device           dev;
+        spinlock_t              spi_lock;
         struct spi_device       *spi;
         struct list_head        device_entry;
 
@@ -85,12 +86,75 @@ MODULE_PARM_DESC(bufsiz, "data bytes in biggest supported SPI message");
 
 /*-------------------------------------------------------------------------*/
 
+/*
+ * We can't use the standard synchronous wrappers for file I/O; we
+ * need to protect against async removal of the underlying spi_device.
+ */
+static void spidev_complete(void *arg)
+{
+        complete(arg);
+}
+
+static ssize_t
+spidev_sync(struct spidev_data *spidev, struct spi_message *message)
+{
+        DECLARE_COMPLETION_ONSTACK(done);
+        int status;
+
+        message->complete = spidev_complete;
+        message->context = &done;
+
+        spin_lock_irq(&spidev->spi_lock);
+        if (spidev->spi == NULL)
+                status = -ESHUTDOWN;
+        else
+                status = spi_async(spidev->spi, message);
+        spin_unlock_irq(&spidev->spi_lock);
+
+        if (status == 0) {
+                wait_for_completion(&done);
+                status = message->status;
+                if (status == 0)
+                        status = message->actual_length;
+        }
+        return status;
+}
+
+static inline ssize_t
+spidev_sync_write(struct spidev_data *spidev, size_t len)
+{
+        struct spi_transfer     t = {
+                        .tx_buf         = spidev->buffer,
+                        .len            = len,
+                };
+        struct spi_message      m;
+
+        spi_message_init(&m);
+        spi_message_add_tail(&t, &m);
+        return spidev_sync(spidev, &m);
+}
+
+static inline ssize_t
+spidev_sync_read(struct spidev_data *spidev, size_t len)
+{
+        struct spi_transfer     t = {
+                        .rx_buf         = spidev->buffer,
+                        .len            = len,
+                };
+        struct spi_message      m;
+
+        spi_message_init(&m);
+        spi_message_add_tail(&t, &m);
+        return spidev_sync(spidev, &m);
+}
+
+/*-------------------------------------------------------------------------*/
+
 /* Read-only message with current device setup */
 static ssize_t
 spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
 {
         struct spidev_data      *spidev;
-        struct spi_device       *spi;
         ssize_t                 status = 0;
 
         /* chipselect only toggles at start or end of operation */
@@ -98,10 +162,9 @@ spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
                 return -EMSGSIZE;
 
         spidev = filp->private_data;
-        spi = spidev->spi;
 
         mutex_lock(&spidev->buf_lock);
-        status = spi_read(spi, spidev->buffer, count);
+        status = spidev_sync_read(spidev, count);
         if (status == 0) {
                 unsigned long   missing;
 
@@ -122,7 +185,6 @@ spidev_write(struct file *filp, const char __user *buf,
                 size_t count, loff_t *f_pos)
 {
         struct spidev_data      *spidev;
-        struct spi_device       *spi;
         ssize_t                 status = 0;
         unsigned long           missing;
 
@@ -131,12 +193,11 @@ spidev_write(struct file *filp, const char __user *buf,
                 return -EMSGSIZE;
 
         spidev = filp->private_data;
-        spi = spidev->spi;
 
         mutex_lock(&spidev->buf_lock);
         missing = copy_from_user(spidev->buffer, buf, count);
         if (missing == 0) {
-                status = spi_write(spi, spidev->buffer, count);
+                status = spidev_sync_write(spidev, count);
                 if (status == 0)
                         status = count;
         } else
@@ -153,7 +214,6 @@ static int spidev_message(struct spidev_data *spidev,
         struct spi_transfer     *k_xfers;
         struct spi_transfer     *k_tmp;
         struct spi_ioc_transfer *u_tmp;
-        struct spi_device       *spi = spidev->spi;
         unsigned                n, total;
         u8                      *buf;
         int                     status = -EFAULT;
@@ -215,7 +275,7 @@ static int spidev_message(struct spidev_data *spidev,
                 spi_message_add_tail(k_tmp, &msg);
         }
 
-        status = spi_sync(spi, &msg);
+        status = spidev_sync(spidev, &msg);
         if (status < 0)
                 goto done;
 
@@ -269,8 +329,16 @@ spidev_ioctl(struct inode *inode, struct file *filp,
         if (err)
                 return -EFAULT;
 
+        /* guard against device removal before, or while,
+         * we issue this ioctl.
+         */
         spidev = filp->private_data;
-        spi = spidev->spi;
+        spin_lock_irq(&spidev->spi_lock);
+        spi = spi_dev_get(spidev->spi);
+        spin_unlock_irq(&spidev->spi_lock);
+
+        if (spi == NULL)
+                return -ESHUTDOWN;
 
         switch (cmd) {
         /* read requests */
@@ -356,8 +424,10 @@ spidev_ioctl(struct inode *inode, struct file *filp,
         default:
                 /* segmented and/or full-duplex I/O request */
                 if (_IOC_NR(cmd) != _IOC_NR(SPI_IOC_MESSAGE(0))
-                                || _IOC_DIR(cmd) != _IOC_WRITE)
-                        return -ENOTTY;
+                                || _IOC_DIR(cmd) != _IOC_WRITE) {
+                        retval = -ENOTTY;
+                        break;
+                }
 
                 tmp = _IOC_SIZE(cmd);
                 if ((tmp % sizeof(struct spi_ioc_transfer)) != 0) {
@@ -385,6 +455,7 @@ spidev_ioctl(struct inode *inode, struct file *filp,
                 kfree(ioc);
                 break;
         }
+        spi_dev_put(spi);
         return retval;
 }
 
@@ -488,6 +559,7 @@ static int spidev_probe(struct spi_device *spi)
 
         /* Initialize the driver data */
         spidev->spi = spi;
+        spin_lock_init(&spidev->spi_lock);
         mutex_init(&spidev->buf_lock);
 
         INIT_LIST_HEAD(&spidev->device_entry);
@@ -526,13 +598,17 @@ static int spidev_remove(struct spi_device *spi)
 {
         struct spidev_data      *spidev = dev_get_drvdata(&spi->dev);
 
-        mutex_lock(&device_list_lock);
+        /* make sure ops on existing fds can abort cleanly */
+        spin_lock_irq(&spidev->spi_lock);
+        spidev->spi = NULL;
+        spin_unlock_irq(&spidev->spi_lock);
 
+        /* prevent new opens */
+        mutex_lock(&device_list_lock);
         list_del(&spidev->device_entry);
         dev_set_drvdata(&spi->dev, NULL);
         clear_bit(MINOR(spidev->dev.devt), minors);
         device_unregister(&spidev->dev);
-
         mutex_unlock(&device_list_lock);
 
         return 0;