scsi: Improve requeuing behavior

Requests are unprepared and reprepared when being requeued.  Avoid that
requeuing resets .jiffies_at_alloc and .retries by initializing these
two member variables from inside scsi_initialize_rq() and by preserving
both member variables when preparing a request. This patch affects the
requeuing behavior of both the legacy scsi and the scsi-mq code paths.

Reported-by: Brian King <brking@linux.vnet.ibm.com>
References: https://lkml.org/lkml/2017/8/18/923 ("Re: [BUG][bisected 270065e] linux-next fails to boot on powerpc")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Brian King <brking@linux.vnet.ibm.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 4bfe0df35823fde3c0864014e5d20c43f6660c58..6085377643ae392e934a1034a20bab6cc90bcc7e 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1112,9 +1112,13 @@ err_exit:
 EXPORT_SYMBOL(scsi_init_io);
 
 /**
- * scsi_initialize_rq - initialize struct scsi_cmnd.req
+ * scsi_initialize_rq - initialize struct scsi_cmnd partially
  * @rq: Request associated with the SCSI command to be initialized.
  *
+ * This function initializes the members of struct scsi_cmnd that must be
+ * initialized before request processing starts and that won't be
+ * reinitialized if a SCSI command is requeued.
+ *
  * Called from inside blk_get_request() for pass-through requests and from
  * inside scsi_init_command() for filesystem requests.
  */
@@ -1123,6 +1127,8 @@ void scsi_initialize_rq(struct request *rq)
        struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
 
        scsi_req_init(&cmd->req);
+       cmd->jiffies_at_alloc = jiffies;
+       cmd->retries = 0;
 }
 EXPORT_SYMBOL(scsi_initialize_rq);
 
@@ -1162,12 +1168,16 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
        void *prot = cmd->prot_sdb;
        struct request *rq = blk_mq_rq_from_pdu(cmd);
        unsigned int flags = cmd->flags & SCMD_PRESERVED_FLAGS;
+       unsigned long jiffies_at_alloc;
+       int retries;
 
        if (!blk_rq_is_scsi(rq) && !(flags & SCMD_INITIALIZED)) {
                flags |= SCMD_INITIALIZED;
                scsi_initialize_rq(rq);
        }
 
+       jiffies_at_alloc = cmd->jiffies_at_alloc;
+       retries = cmd->retries;
        /* zero out the cmd, except for the embedded scsi_request */
        memset((char *)cmd + sizeof(cmd->req), 0,
                sizeof(*cmd) - sizeof(cmd->req) + dev->host->hostt->cmd_size);
@@ -1177,7 +1187,8 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
        cmd->prot_sdb = prot;
        cmd->flags = flags;
        INIT_DELAYED_WORK(&cmd->abort_work, scmd_eh_abort_handler);
-       cmd->jiffies_at_alloc = jiffies;
+       cmd->jiffies_at_alloc = jiffies_at_alloc;
+       cmd->retries = retries;
 
        scsi_add_cmd_to_list(cmd);
 }