Merge tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi

Pull misc SCSI patches from James Bottomley:
 "This is a short patch set representing a couple of left overs from the
  merge window (debug removal and MAINTAINER changes).

  Plus one merge window regression (the local workqueue for hpsa) and a
  set of bug fixes for several issues (two for scsi-mq and the rest an
  assortment of long standing stuff, all cc'd to stable)"

* tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
  sg: fix EWOULDBLOCK errors with scsi-mq
  sg: fix unkillable I/O wait deadlock with scsi-mq
  sg: fix read() error reporting
  wd719x: add missing .module to wd719x_template
  hpsa: correct compiler warnings introduced by hpsa-add-local-workqueue patch
  fixed invalid assignment of 64bit mask to host dma_boundary for scatter gather segment boundary limit.
  fcoe: Transition maintainership to Vasu
  am53c974: remove left-over debugging code

1 files changed, 33 insertions, 7 deletions

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 0cbc1fb45f10..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
@@ -1335,6 +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)
@@ -1669,7 +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);
@@ -1759,10 +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);