svn commit: r349923 - head/sys/kern

[Doug Moore]

Author: dougm
Date: Thu Jul 11 20:52:39 2019
New Revision: 349923
URL: https://svnweb.freebsd.org/changeset/base/349923

Log:
  Address problems in blist_alloc introduced in r349777.  The swap block allocator could become corrupted
  if a retry to allocate swap space, after a larger allocation attempt failed, allocated a smaller set of free blocks
  that ended on a 32- or 64-block boundary.
  
  Add tests to detect this kind of failure-to-extend-at-boundary and prevent the associated accounting screwup.
  
  Reported by: pho
  Tested by: pho
  Reviewed by: alc
  Approved by: markj (mentor)
  Discussed with: kib
  Differential Revision: https://reviews.freebsd.org/D20893

Modified:
  head/sys/kern/subr_blist.c

Modified: head/sys/kern/subr_blist.c
==============================================================================
--- head/sys/kern/subr_blist.c	Thu Jul 11 20:29:50 2019	(r349922)
+++ head/sys/kern/subr_blist.c	Thu Jul 11 20:52:39 2019	(r349923)
@@ -639,15 +639,27 @@ blst_next_leaf_alloc(blmeta_t *scan, daddr_t start, in
 			 * bitpos() returns zero here.
 			 */
 			avail = blk - start + bitpos(~scan->bm_bitmap);
-			if (avail < count) {
+			if (avail < count || avail == 0) {
 				/*
 				 * There isn't a next leaf with enough free
-				 * blocks at its beginning to complete the
-				 * spanning allocation.
+				 * blocks at its beginning to bother
+				 * allocating.
 				 */
 				return (avail);
 			}
 			maxcount = imin(avail, maxcount);
+			if (maxcount % BLIST_BMAP_RADIX == 0) {
+				/*
+				 * There was no next leaf.  Back scan up to
+				 * last leaf.
+				 */
+				--scan;
+				while (radix != BLIST_BMAP_RADIX) {
+					radix /= BLIST_META_RADIX;
+					--scan;
+				}
+				blk -= BLIST_BMAP_RADIX;
+			}
 		}
 	}