[SCSI] sd: Fix refcounting

Currently the driver takes a reference only for requests coming by way
of the gendisk, not for requests coming by way of the struct device or
struct scsi_device.  Such requests can arrive in the rescan, flush,
and shutdown pathways.

The patch also makes the scsi_disk keep a reference to the underlying
scsi_device, and it erases the scsi_device's pointer to the scsi_disk
when the scsi_device is removed (since the pointer should no longer be
used).

This resolves Bugzilla entry #5237.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

1 files changed, 62 insertions, 37 deletions

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 9de8e186cb6..bb5b242ac6b 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -177,24 +177,38 @@ static inline struct scsi_disk *scsi_disk(struct gendisk *disk)
         return container_of(disk->private_data, struct scsi_disk, driver);
 }
 
-static struct scsi_disk *scsi_disk_get(struct gendisk *disk)
+static struct scsi_disk *__scsi_disk_get(struct gendisk *disk)
 {
         struct scsi_disk *sdkp = NULL;
 
+        if (disk->private_data) {
+                sdkp = scsi_disk(disk);
+                if (scsi_device_get(sdkp->device) == 0)
+                        kref_get(&sdkp->kref);
+                else
+                        sdkp = NULL;
+        }
+        return sdkp;
+}
+
+static struct scsi_disk *scsi_disk_get(struct gendisk *disk)
+{
+        struct scsi_disk *sdkp;
+
         down(&sd_ref_sem);
-        if (disk->private_data == NULL)
-                goto out;
-        sdkp = scsi_disk(disk);
-        kref_get(&sdkp->kref);
-        if (scsi_device_get(sdkp->device))
-                goto out_put;
+        sdkp = __scsi_disk_get(disk);
         up(&sd_ref_sem);
         return sdkp;
+}
 
- out_put:
-        kref_put(&sdkp->kref, scsi_disk_release);
-        sdkp = NULL;
- out:
+static struct scsi_disk *scsi_disk_get_from_dev(struct device *dev)
+{
+        struct scsi_disk *sdkp;
+
+        down(&sd_ref_sem);
+        sdkp = dev_get_drvdata(dev);
+        if (sdkp)
+                sdkp = __scsi_disk_get(sdkp->disk);
         up(&sd_ref_sem);
         return sdkp;
 }
@@ -716,16 +730,17 @@ static int sd_sync_cache(struct scsi_device *sdp)
 
 static int sd_issue_flush(struct device *dev, sector_t *error_sector)
 {
+        int ret = 0;
         struct scsi_device *sdp = to_scsi_device(dev);
-        struct scsi_disk *sdkp = dev_get_drvdata(dev);
+        struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
 
         if (!sdkp)
                return -ENODEV;
 
-        if (!sdkp->WCE)
-                return 0;
-
-        return sd_sync_cache(sdp);
+        if (sdkp->WCE)
+                ret = sd_sync_cache(sdp);
+        scsi_disk_put(sdkp);
+        return ret;
 }
 
 static void sd_end_flush(request_queue_t *q, struct request *flush_rq)
@@ -754,23 +769,30 @@ static void sd_end_flush(request_queue_t *q, struct request *flush_rq)
 static int sd_prepare_flush(request_queue_t *q, struct request *rq)
 {
         struct scsi_device *sdev = q->queuedata;
-        struct scsi_disk *sdkp = dev_get_drvdata(&sdev->sdev_gendev);
-
-        if (sdkp->WCE) {
-                memset(rq->cmd, 0, sizeof(rq->cmd));
-                rq->flags |= REQ_BLOCK_PC | REQ_SOFTBARRIER;
-                rq->timeout = SD_TIMEOUT;
-                rq->cmd[0] = SYNCHRONIZE_CACHE;
-                return 1;
+        struct scsi_disk *sdkp = scsi_disk_get_from_dev(&sdev->sdev_gendev);
+        int ret = 0;
+
+        if (sdkp) {
+                if (sdkp->WCE) {
+                        memset(rq->cmd, 0, sizeof(rq->cmd));
+                        rq->flags |= REQ_BLOCK_PC | REQ_SOFTBARRIER;
+                        rq->timeout = SD_TIMEOUT;
+                        rq->cmd[0] = SYNCHRONIZE_CACHE;
+                        ret = 1;
+                }
+                scsi_disk_put(sdkp);
         }
-
-        return 0;
+        return ret;
 }
 
 static void sd_rescan(struct device *dev)
 {
-        struct scsi_disk *sdkp = dev_get_drvdata(dev);
-        sd_revalidate_disk(sdkp->disk);
+        struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
+
+        if (sdkp) {
+                sd_revalidate_disk(sdkp->disk);
+                scsi_disk_put(sdkp);
+        }
 }
 
 
@@ -1561,6 +1583,7 @@ static int sd_probe(struct device *dev)
         if (error)
                 goto out_put;
 
+        get_device(&sdp->sdev_gendev);
         sdkp->device = sdp;
         sdkp->driver = &sd_template;
         sdkp->disk = gd;
@@ -1637,7 +1660,9 @@ static int sd_remove(struct device *dev)
 
         del_gendisk(sdkp->disk);
         sd_shutdown(dev);
+
         down(&sd_ref_sem);
+        dev_set_drvdata(dev, NULL);
         kref_put(&sdkp->kref, scsi_disk_release);
         up(&sd_ref_sem);
 
@@ -1663,8 +1688,8 @@ static void scsi_disk_release(struct kref *kref)
         spin_unlock(&sd_index_lock);
 
         disk->private_data = NULL;
-
         put_disk(disk);
+        put_device(&sdkp->device->sdev_gendev);
 
         kfree(sdkp);
 }
@@ -1677,18 +1702,18 @@ static void scsi_disk_release(struct kref *kref)
 static void sd_shutdown(struct device *dev)
 {
         struct scsi_device *sdp = to_scsi_device(dev);
-        struct scsi_disk *sdkp = dev_get_drvdata(dev);
+        struct scsi_disk *sdkp = scsi_disk_get_from_dev(dev);
 
         if (!sdkp)
                 return;         /* this can happen */
 
-        if (!sdkp->WCE)
-                return;
-
-        printk(KERN_NOTICE "Synchronizing SCSI cache for disk %s: \n",
-                        sdkp->disk->disk_name);
-        sd_sync_cache(sdp);
-}       
+        if (sdkp->WCE) {
+                printk(KERN_NOTICE "Synchronizing SCSI cache for disk %s: \n",
+                                sdkp->disk->disk_name);
+                sd_sync_cache(sdp);
+        }
+        scsi_disk_put(sdkp);
+}
 
 /**
  *      init_sd - entry point for this driver (both when built in or when