svn commit: r324944 - head/sys/cam

[Warner Losh]

Author: imp
Date: Tue Oct 24 02:25:42 2017
New Revision: 324944
URL: https://svnweb.freebsd.org/changeset/base/324944

Log:
  Treat a 'current' value of 0 as unlimited as a failsfe.
  
  When limiting I/O, a value of 0 makes no sense as a limit. No progress
  can be made. Trade the possibility that someone might be doing
  something clever to achieve ultra-low I/O limits vs the damage of not
  ever making progress on an I/O in favor of making progress. Now the
  machine won't be useless if this accidentally gets requested.
  
  Sponsored by: Netflix

Modified:
  head/sys/cam/cam_iosched.c

Modified: head/sys/cam/cam_iosched.c
==============================================================================
--- head/sys/cam/cam_iosched.c	Tue Oct 24 00:51:11 2017	(r324943)
+++ head/sys/cam/cam_iosched.c	Tue Oct 24 02:25:42 2017	(r324944)
@@ -457,9 +457,10 @@ cam_iosched_iops_caniop(struct iop_stats *ios, struct 
 
 	/*
 	 * So if we have any more IOPs left, allow it,
-	 * otherwise wait.
+	 * otherwise wait. If current iops is 0, treat that
+	 * as unlimited as a failsafe.
 	 */
-	if (ios->l_value1 <= 0)
+	if (ios->current > 0 && ios->l_value1 <= 0)
 		return EAGAIN;
 	return 0;
 }
@@ -525,8 +526,11 @@ cam_iosched_bw_caniop(struct iop_stats *ios, struct bi
 	 * what we let through this quantum (to prevent the
 	 * starvation), at the cost of getting a little less
 	 * next quantum.
+	 *
+	 * Also note that if the current limit is <= 0,
+	 * we treat it as unlimited as a failsafe.
 	 */
-	if (ios->l_value1 <= 0)
+	if (ios->current > 0 && ios->l_value1 <= 0)
 		return EAGAIN;