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>

3 files changed, 27 insertions, 12 deletions

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index dd338a8cd275..16eef068e9e9 100644
--- a/drivers/scsi/scsi_error.c
+++ b/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);
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 0df15cb738d2..0dbf25512778 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/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)
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index d6fd2aba0380..3de905e205ce 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/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 */
 };