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>

1 files changed, 15 insertions, 8 deletions

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 14ec8f521ae8..4056004102ae 100644
--- 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);