[SCSI] sg: protect sdp->exclude

Changes since v1: set_exclude now returns the new value, which gets
rid of the comma expression and the operator precedence bug.  Thanks
to Douglas for spotting it.

sdp->exclude was previously protected by the BKL.  The sg_mutex, which
replaced the BKL, only semi-protected it, as it was missing from
sg_release() and sg_proc_seq_show_debug().  Take an explicit spinlock
for it.

Signed-off-by: Joern Engel <joern@logfs.org>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 4a00364445f02ae8fc52411ed268f3b55f5277a3..8e15c448a761b782500239cada633364fe56a6ed 100644 (file)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -105,6 +105,7 @@ static int sg_add(struct device *, struct class_interface *);
 static void sg_remove(struct device *, struct class_interface *);
 
 static DEFINE_MUTEX(sg_mutex);
+static DEFINE_SPINLOCK(sg_open_exclusive_lock);
 
 static DEFINE_IDR(sg_index_idr);
 static DEFINE_RWLOCK(sg_index_lock);   /* Also used to lock
@@ -173,7 +174,8 @@ typedef struct sg_device { /* holds the state of each scsi generic device */
        u32 index;              /* device index number */
        struct list_head sfds;
        volatile char detached; /* 0->attached, 1->detached pending removal */
-       volatile char exclude;  /* opened for exclusive access */
+       /* exclude protected by sg_open_exclusive_lock */
+       char exclude;           /* opened for exclusive access */
        char sgdebug;           /* 0->off, 1->sense, 9->dump dev, 10-> all devs */
        struct gendisk *disk;
        struct cdev * cdev;     /* char_dev [sysfs: /sys/cdev/major/sg<n>] */
@@ -221,6 +223,27 @@ static int sg_allow_access(struct file *filp, unsigned char *cmd)
        return blk_verify_command(cmd, filp->f_mode & FMODE_WRITE);
 }
 
+static int get_exclude(Sg_device *sdp)
+{
+       unsigned long flags;
+       int ret;
+
+       spin_lock_irqsave(&sg_open_exclusive_lock, flags);
+       ret = sdp->exclude;
+       spin_unlock_irqrestore(&sg_open_exclusive_lock, flags);
+       return ret;
+}
+
+static int set_exclude(Sg_device *sdp, char val)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&sg_open_exclusive_lock, flags);
+       sdp->exclude = val;
+       spin_unlock_irqrestore(&sg_open_exclusive_lock, flags);
+       return val;
+}
+
 static int
 sg_open(struct inode *inode, struct file *filp)
 {
@@ -269,17 +292,17 @@ sg_open(struct inode *inode, struct file *filp)
                        goto error_out;
                }
                res = wait_event_interruptible(sdp->o_excl_wait,
-                                          ((!list_empty(&sdp->sfds) || sdp->exclude) ? 0 : (sdp->exclude = 1)));
+                                          ((!list_empty(&sdp->sfds) || get_exclude(sdp)) ? 0 : set_exclude(sdp, 1)));
                if (res) {
                        retval = res;   /* -ERESTARTSYS because signal hit process */
                        goto error_out;
                }
-       } else if (sdp->exclude) {      /* some other fd has an exclusive lock on dev */
+       } else if (get_exclude(sdp)) {  /* some other fd has an exclusive lock on dev */
                if (flags & O_NONBLOCK) {
                        retval = -EBUSY;
                        goto error_out;
                }
-               res = wait_event_interruptible(sdp->o_excl_wait, !sdp->exclude);
+               res = wait_event_interruptible(sdp->o_excl_wait, !get_exclude(sdp));
                if (res) {
                        retval = res;   /* -ERESTARTSYS because signal hit process */
                        goto error_out;
@@ -298,7 +321,7 @@ sg_open(struct inode *inode, struct file *filp)
                filp->private_data = sfp;
        else {
                if (flags & O_EXCL) {
-                       sdp->exclude = 0;       /* undo if error */
+                       set_exclude(sdp, 0);    /* undo if error */
                        wake_up_interruptible(&sdp->o_excl_wait);
                }
                retval = -ENOMEM;
@@ -329,7 +352,7 @@ sg_release(struct inode *inode, struct file *filp)
                return -ENXIO;
        SCSI_LOG_TIMEOUT(3, printk("sg_release: %s\n", sdp->disk->disk_name));
 
-       sdp->exclude = 0;
+       set_exclude(sdp, 0);
        wake_up_interruptible(&sdp->o_excl_wait);
 
        scsi_autopm_put_device(sdp->device);
@@ -2606,7 +2629,7 @@ static int sg_proc_seq_show_debug(struct seq_file *s, void *v)
                             scsidp->lun,
                             scsidp->host->hostt->emulated);
                seq_printf(s, " sg_tablesize=%d excl=%d\n",
-                          sdp->sg_tablesize, sdp->exclude);
+                          sdp->sg_tablesize, get_exclude(sdp));
                sg_proc_debug_helper(s, sdp);
        }
        read_unlock_irqrestore(&sg_index_lock, iflags);