iscsi-target: Fix iscsit_alloc_buffs() failure cases

Make iscsit_alloc_buffs() failure case for page_alloc_failed use correct
__free_page() SGL pointer, and return -ENOMEM for iscsit_allocate_iovecs
failure to push se_cmd->t_mem_sg release into iscsit_release_cmd()
callback during iscsit_add_reject_from_cmd() connection reset.

Also drop cmd->t_mem_sg = NULL assignment from page_alloc_failed
failure case.

Reported-by: Roland Dreier <roland@purestorage.com>
Cc: Andy Grover <agrover@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.c

@@ -780,7 +780,7 @@ static int iscsit_alloc_buffs(struct iscsi_cmd *cmd)
 	struct scatterlist *sgl;
 	u32 length = cmd->se_cmd.data_length;
 	int nents = DIV_ROUND_UP(length, PAGE_SIZE);
-	int i = 0, ret;
+	int i = 0, j = 0, ret;
 	/*
 	 * If no SCSI payload is present, allocate the default iovecs used for
 	 * iSCSI PDU Header
@@ -821,17 +821,15 @@ static int iscsit_alloc_buffs(struct iscsi_cmd *cmd)
 	 */
         ret = iscsit_allocate_iovecs(cmd);
         if (ret < 0)
-		goto page_alloc_failed;
+		return -ENOMEM;
 
 	return 0;
 
 page_alloc_failed:
-	while (i >= 0) {
-		__free_page(sg_page(&sgl[i]));
-		i--;
-	}
-	kfree(cmd->t_mem_sg);
-	cmd->t_mem_sg = NULL;
+	while (j < i)
+		__free_page(sg_page(&sgl[j++]));
+
+	kfree(sgl);
 	return -ENOMEM;
 }