sd: notify block layer when using temporary change to cache_type

This is a fix for commit 39c60a0948cc06139e2fbfe084f83cb7e7deae3b

  "sd: fix array cache flushing bug causing performance problems"

We must notify the block layer via q->flush_flags after a temporary change
of the cache_type to write through.  Without this, a SYNCHRONIZE CACHE
command will still be generated.  This patch factors out a helper that
can be called from sd_revalidate_disk and cache_type_store.

Signed-off-by: Vaughan Cao <vaughan.cao@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 14ec8f5..4056004 100644 (file)
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -134,6 +134,19 @@ static const char *sd_cache_types[] = {
        "write back, no read (daft)"
 };
 
+static void sd_set_flush_flag(struct scsi_disk *sdkp)
+{
+       unsigned flush = 0;
+
+       if (sdkp->WCE) {
+               flush |= REQ_FLUSH;
+               if (sdkp->DPOFUA)
+                       flush |= REQ_FUA;
+       }
+
+       blk_queue_flush(sdkp->disk->queue, flush);
+}
+
 static ssize_t
 cache_type_store(struct device *dev, struct device_attribute *attr,
                 const char *buf, size_t count)
@@ -177,6 +190,7 @@ cache_type_store(struct device *dev, struct device_attribute *attr,
        if (sdkp->cache_override) {
                sdkp->WCE = wce;
                sdkp->RCD = rcd;
+               sd_set_flush_flag(sdkp);
                return count;
        }
 
@@ -2698,7 +2712,6 @@ static int sd_revalidate_disk(struct gendisk *disk)
        struct scsi_disk *sdkp = scsi_disk(disk);
        struct scsi_device *sdp = sdkp->device;
        unsigned char *buffer;
-       unsigned flush = 0;
 
        SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp,
                                      "sd_revalidate_disk\n"));
@@ -2744,13 +2757,7 @@ static int sd_revalidate_disk(struct gendisk *disk)
         * We now have all cache related info, determine how we deal
         * with flush requests.
         */
-       if (sdkp->WCE) {
-               flush |= REQ_FLUSH;
-               if (sdkp->DPOFUA)
-                       flush |= REQ_FUA;
-       }
-
-       blk_queue_flush(sdkp->disk->queue, flush);
+       sd_set_flush_flag(sdkp);
 
        set_capacity(disk, sdkp->capacity);
        sd_config_write_same(sdkp);