Merge branch 'iocb' into for-next

[karo-tx-linux.git] / drivers / scsi / sg.c

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index c78a6f7bbc209390ecd5426f5e9d00174fdd978c..d383f84869aa45475bb25f149123092a0f3beb0c 100644 (file)
--- 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);