[SCSI] sg: completely protect sfds

sfds is protected by sg_index_lock - except for sg_open(), where it
isn't.  Change that and add some documentation.

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

1 files changed, 16 insertions, 3 deletions

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 8e15c448a761..53af8089dcb9 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -146,6 +146,7 @@ typedef struct sg_request {	/* SG_MAX_QUEUE requests outstanding per file */
 } Sg_request;
 
 typedef struct sg_fd {          /* holds the state of a file descriptor */
+        /* sfd_siblings is protected by sg_index_lock */
         struct list_head sfd_siblings;
         struct sg_device *parentdp;     /* owning device */
         wait_queue_head_t read_wait;    /* queue read until command done */
@@ -172,6 +173,7 @@ typedef struct sg_device { /* holds the state of each scsi generic device */
         wait_queue_head_t o_excl_wait;  /* queue open() when O_EXCL in use */
         int sg_tablesize;       /* adapter's max scatter-gather table size */
         u32 index;              /* device index number */
+        /* sfds is protected by sg_index_lock */
         struct list_head sfds;
         volatile char detached; /* 0->attached, 1->detached pending removal */
         /* exclude protected by sg_open_exclusive_lock */
@@ -244,6 +246,17 @@ static int set_exclude(Sg_device *sdp, char val)
         return val;
 }
 
+static int sfds_list_empty(Sg_device *sdp)
+{
+        unsigned long flags;
+        int ret;
+
+        read_lock_irqsave(&sg_index_lock, flags);
+        ret = list_empty(&sdp->sfds);
+        read_unlock_irqrestore(&sg_index_lock, flags);
+        return ret;
+}
+
 static int
 sg_open(struct inode *inode, struct file *filp)
 {
@@ -287,12 +300,12 @@ sg_open(struct inode *inode, struct file *filp)
                         retval = -EPERM; /* Can't lock it with read only access */
                         goto error_out;
                 }
-                if (!list_empty(&sdp->sfds) && (flags & O_NONBLOCK)) {
+                if (!sfds_list_empty(sdp) && (flags & O_NONBLOCK)) {
                         retval = -EBUSY;
                         goto error_out;
                 }
                 res = wait_event_interruptible(sdp->o_excl_wait,
-                                           ((!list_empty(&sdp->sfds) || get_exclude(sdp)) ? 0 : set_exclude(sdp, 1)));
+                                           ((!sfds_list_empty(sdp) || get_exclude(sdp)) ? 0 : set_exclude(sdp, 1)));
                 if (res) {
                         retval = res;   /* -ERESTARTSYS because signal hit process */
                         goto error_out;
@@ -312,7 +325,7 @@ sg_open(struct inode *inode, struct file *filp)
                 retval = -ENODEV;
                 goto error_out;
         }
-        if (list_empty(&sdp->sfds)) {   /* no existing opens on this device */
+        if (sfds_list_empty(sdp)) {     /* no existing opens on this device */
                 sdp->sgdebug = 0;
                 q = sdp->device->request_queue;
                 sdp->sg_tablesize = queue_max_segments(q);