[PATCH v3 3/4] sd: Make synchronize cache upon shutdown asynchronous

[Bart Van Assche]

This patch avoids that sd_shutdown() hangs on the SYNCHRONIZE CACHE
command if the block layer queue has been stopped by
scsi_target_block().

Signed-off-by: Bart Van Assche <bart.vanass...@sandisk.com>
Cc: Israel Rukshin <isra...@mellanox.com>
Cc: Max Gurtovoy <m...@mellanox.com>
Cc: Hannes Reinecke <h...@suse.de>
Cc: Benjamin Block <bbl...@linux.vnet.ibm.com>
---
 drivers/scsi/sd.c | 45 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 40 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index fe0f7997074e..deff564fe649 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1489,6 +1489,33 @@ static unsigned int sd_check_events(struct gendisk 
*disk, unsigned int clearing)
        return retval;
 }
 
+static void sd_sync_cache_done(struct request *rq, int e)
+{
+       struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
+
+       sd_printk(KERN_DEBUG, sdkp, "%s\n", __func__);
+
+       blk_put_request(rq);
+}
+
+/*
+ * Issue a SYNCHRONIZE CACHE command asynchronously. Since blk_cleanup_queue()
+ * waits for all commands to finish, __scsi_remove_device() will wait for the
+ * SYNCHRONIZE CACHE command to finish.
+ */
+static int sd_sync_cache_async(struct scsi_disk *sdkp)
+{
+       const struct scsi_device *sdp = sdkp->device;
+       const int timeout = sdp->request_queue->rq_timeout *
+                           SD_FLUSH_TIMEOUT_MULTIPLIER;
+       const unsigned char cmd[10] = { SYNCHRONIZE_CACHE };
+
+       sd_printk(KERN_DEBUG, sdkp, "%s\n", __func__);
+       return scsi_execute_async(sdp, sdkp->disk, cmd, DMA_NONE, NULL, 0,
+                                 timeout, SD_MAX_RETRIES, 0, 0,
+                                 sd_sync_cache_done);
+}
+
 static int sd_sync_cache(struct scsi_disk *sdkp)
 {
        int retries, res;
@@ -3349,13 +3376,15 @@ static int sd_start_stop_device(struct scsi_disk *sdkp, 
int start)
 }
 
 /*
- * Send a SYNCHRONIZE CACHE instruction down to the device through
- * the normal SCSI command structure.  Wait for the command to
- * complete.
+ * Send a SYNCHRONIZE CACHE instruction down to the device through the normal
+ * SCSI command structure. When stopping the disk, wait for the command to
+ * complete. When not stopping the disk, the blk_cleanup_queue() call in
+ * __scsi_remove_device() will wait for this command to complete.
  */
 static void sd_shutdown(struct device *dev)
 {
        struct scsi_disk *sdkp = dev_get_drvdata(dev);
+       bool stop_disk;
 
        if (!sdkp)
                return;         /* this can happen */
@@ -3363,12 +3392,18 @@ static void sd_shutdown(struct device *dev)
        if (pm_runtime_suspended(dev))
                return;
 
+       stop_disk = system_state != SYSTEM_RESTART &&
+               sdkp->device->manage_start_stop;
+
        if (sdkp->WCE && sdkp->media_present) {
                sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
-               sd_sync_cache(sdkp);
+               if (stop_disk)
+                       sd_sync_cache(sdkp);
+               else
+                       sd_sync_cache_async(sdkp);
        }
 
-       if (system_state != SYSTEM_RESTART && sdkp->device->manage_start_stop) {
+       if (stop_disk) {
                sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
                sd_start_stop_device(sdkp, 0);
        }
-- 
2.12.2