scsi: Do not rely on blk-mq for double completions

The scsi timeout error handling had been directly updating the block
layer's request state to prevent a error handling and a natural completion
from completing the same request twice. Fix this layering violation
by having scsi control the fate of its commands with scsi owned flags
rather than use blk-mq's.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/scsi_error.c

@@ -297,19 +297,19 @@ enum blk_eh_timer_return scsi_times_out(struct request *req)
 
 	if (rtn == BLK_EH_DONE) {
 		/*
-		 * For blk-mq, we must set the request state to complete now
-		 * before sending the request to the scsi error handler. This
-		 * will prevent a use-after-free in the event the LLD manages
-		 * to complete the request before the error handler finishes
-		 * processing this timed out request.
+		 * Set the command to complete first in order to prevent a real
+		 * completion from releasing the command while error handling
+		 * is using it. If the command was already completed, then the
+		 * lower level driver beat the timeout handler, and it is safe
+		 * to return without escalating error recovery.
 		 *
-		 * If the request was already completed, then the LLD beat the
-		 * time out handler from transferring the request to the scsi
-		 * error handler. In that case we can return immediately as no
-		 * further action is required.
+		 * If timeout handling lost the race to a real completion, the
+		 * block layer may ignore that due to a fake timeout injection,
+		 * so return RESET_TIMER to allow error handling another shot
+		 * at this command.
 		 */
-		if (!blk_mq_mark_complete(req))
-			return rtn;
+		if (test_and_set_bit(SCMD_STATE_COMPLETE, &scmd->state))
+			return BLK_EH_RESET_TIMER;
 		if (scsi_abort_command(scmd) != SUCCESS) {
 			set_host_byte(scmd, DID_TIME_OUT);
 			scsi_eh_scmd_add(scmd);

drivers/scsi/scsi_lib.c

@@ -1642,8 +1642,18 @@ static blk_status_t scsi_mq_prep_fn(struct request *req)
 
 static void scsi_mq_done(struct scsi_cmnd *cmd)
 {
+	if (unlikely(test_and_set_bit(SCMD_STATE_COMPLETE, &cmd->state)))
+		return;
 	trace_scsi_dispatch_cmd_done(cmd);
-	blk_mq_complete_request(cmd->request);
+
+	/*
+	 * If the block layer didn't complete the request due to a timeout
+	 * injection, scsi must clear its internal completed state so that the
+	 * timeout handler will see it needs to escalate its own error
+	 * recovery.
+	 */
+	if (unlikely(!blk_mq_complete_request(cmd->request)))
+		clear_bit(SCMD_STATE_COMPLETE, &cmd->state);
 }
 
 static void scsi_mq_put_budget(struct blk_mq_hw_ctx *hctx)
@@ -1702,6 +1712,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 	if (!scsi_host_queue_ready(q, shost, sdev))
 		goto out_dec_target_busy;
 
+	clear_bit(SCMD_STATE_COMPLETE, &cmd->state);
 	if (!(req->rq_flags & RQF_DONTPREP)) {
 		ret = scsi_mq_prep_fn(req);
 		if (ret != BLK_STS_OK)

include/scsi/scsi_cmnd.h

@@ -61,6 +61,9 @@ struct scsi_pointer {
 /* flags preserved across unprep / reprep */
 #define SCMD_PRESERVED_FLAGS	(SCMD_UNCHECKED_ISA_DMA | SCMD_INITIALIZED)
 
+/* for scmd->state */
+#define SCMD_STATE_COMPLETE	(1 << 0)
+
 struct scsi_cmnd {
 	struct scsi_request req;
 	struct scsi_device *device;
@@ -145,6 +148,7 @@ struct scsi_cmnd {
 
 	int result;		/* Status code from lower level driver */
 	int flags;		/* Command flags */
+	unsigned long state;	/* Command completion state */
 
 	unsigned char tag;	/* SCSI-II queued command tag */
 };