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path: root/drivers/scsi/sg.c
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Diffstat (limited to 'drivers/scsi/sg.c')
-rw-r--r--drivers/scsi/sg.c40
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);