1 files changed, 40 insertions, 32 deletions

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index b14f64cb9724..2270bd51f9c2 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -546,7 +546,7 @@ static ssize_t
 sg_new_read(Sg_fd * sfp, char __user *buf, size_t count, Sg_request * srp)
 {
 	sg_io_hdr_t *hp = &srp->header;
-	int err = 0;
+	int err = 0, err2;
 	int len;
 
 	if (count < SZ_SG_IO_HDR) {
@@ -575,8 +575,8 @@ sg_new_read(Sg_fd * sfp, char __user *buf, size_t count, Sg_request * srp)
 		goto err_out;
 	}
 err_out:
-	err = sg_finish_rem_req(srp);
-	return (0 == err) ? count : err;
+	err2 = sg_finish_rem_req(srp);
+	return err ? : err2 ? : count;
 }
 
 static ssize_t
@@ -763,7 +763,7 @@ static int
 sg_common_write(Sg_fd * sfp, Sg_request * srp,
 		unsigned char *cmnd, int timeout, int blocking)
 {
-	int k, data_dir, at_head;
+	int k, at_head;
 	Sg_device *sdp = sfp->parentdp;
 	sg_io_hdr_t *hp = &srp->header;
 
@@ -793,21 +793,6 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
 		return -ENODEV;
 	}
 
-	switch (hp->dxfer_direction) {
-	case SG_DXFER_TO_FROM_DEV:
-	case SG_DXFER_FROM_DEV:
-		data_dir = DMA_FROM_DEVICE;
-		break;
-	case SG_DXFER_TO_DEV:
-		data_dir = DMA_TO_DEVICE;
-		break;
-	case SG_DXFER_UNKNOWN:
-		data_dir = DMA_BIDIRECTIONAL;
-		break;
-	default:
-		data_dir = DMA_NONE;
-		break;
-	}
 	hp->duration = jiffies_to_msecs(jiffies);
 	if (hp->interface_id != '\0' &&	/* v3 (or later) interface */
 	    (SG_FLAG_Q_AT_TAIL & hp->flags))
@@ -1350,6 +1335,17 @@ sg_rq_end_io(struct request *rq, int uptodate)
 	}
 	/* Rely on write phase to clean out srp status values, so no "else" */
 
+	/*
+	 * Free the request as soon as it is complete so that its resources
+	 * can be reused without waiting for userspace to read() the
+	 * result.  But keep the associated bio (if any) around until
+	 * blk_rq_unmap_user() can be called from user context.
+	 */
+	srp->rq = NULL;
+	if (rq->cmd != rq->__cmd)
+		kfree(rq->cmd);
+	__blk_put_request(rq->q, rq);
+
 	write_lock_irqsave(&sfp->rq_list_lock, iflags);
 	if (unlikely(srp->orphan)) {
 		if (sfp->keep_orphan)
@@ -1684,7 +1680,22 @@ sg_start_req(Sg_request *srp, unsigned char *cmd)
 			return -ENOMEM;
 	}
 
-	rq = blk_get_request(q, rw, GFP_ATOMIC);
+	/*
+	 * NOTE
+	 *
+	 * With scsi-mq enabled, there are a fixed number of preallocated
+	 * requests equal in number to shost->can_queue.  If all of the
+	 * preallocated requests are already in use, then using GFP_ATOMIC with
+	 * blk_get_request() will return -EWOULDBLOCK, whereas using GFP_KERNEL
+	 * will cause blk_get_request() to sleep until an active command
+	 * completes, freeing up a request.  Neither option is ideal, but
+	 * GFP_KERNEL is the better choice to prevent userspace from getting an
+	 * unexpected EWOULDBLOCK.
+	 *
+	 * With scsi-mq disabled, blk_get_request() with GFP_KERNEL usually
+	 * does not sleep except under memory pressure.
+	 */
+	rq = blk_get_request(q, rw, GFP_KERNEL);
 	if (IS_ERR(rq)) {
 		kfree(long_cmdp);
 		return PTR_ERR(rq);
@@ -1734,22 +1745,19 @@ sg_start_req(Sg_request *srp, unsigned char *cmd)
 	}
 
 	if (iov_count) {
-		int len, size = sizeof(struct sg_iovec) * iov_count;
+		int size = sizeof(struct iovec) * iov_count;
 		struct iovec *iov;
+		struct iov_iter i;
 
 		iov = memdup_user(hp->dxferp, size);
 		if (IS_ERR(iov))
 			return PTR_ERR(iov);
 
-		len = iov_length(iov, iov_count);
-		if (hp->dxfer_len < len) {
-			iov_count = iov_shorten(iov, iov_count, hp->dxfer_len);
-			len = hp->dxfer_len;
-		}
+		iov_iter_init(&i, rw, iov, iov_count,
+			      min_t(size_t, hp->dxfer_len,
+				    iov_length(iov, iov_count)));
 
-		res = blk_rq_map_user_iov(q, rq, md, (struct sg_iovec *)iov,
-					  iov_count,
-					  len, GFP_ATOMIC);
+		res = blk_rq_map_user_iov(q, rq, md, &i, GFP_ATOMIC);
 		kfree(iov);
 	} else
 		res = blk_rq_map_user(q, rq, md, hp->dxferp,
@@ -1777,10 +1785,10 @@ sg_finish_rem_req(Sg_request *srp)
 	SCSI_LOG_TIMEOUT(4, sg_printk(KERN_INFO, sfp->parentdp,
 				      "sg_finish_rem_req: res_used=%d\n",
 				      (int) srp->res_used));
-	if (srp->rq) {
-		if (srp->bio)
-			ret = blk_rq_unmap_user(srp->bio);
+	if (srp->bio)
+		ret = blk_rq_unmap_user(srp->bio);
 
+	if (srp->rq) {
 		if (srp->rq->cmd != srp->rq->__cmd)
 			kfree(srp->rq->cmd);
 		blk_put_request(srp->rq);