svn commit: r368756 - head/contrib/jemalloc/src

[Marcin Wojtas]

Author: mw
Date: Fri Dec 18 10:09:21 2020
New Revision: 368756
URL: https://svnweb.freebsd.org/changeset/base/368756

Log:
  Fix abort in jemalloc extent coalescing.
  
  Fix error in extent_try_coalesce_impl(), which could cause abort
  to happen when trying to coalesce extents backwards. The error could
  happen because of how extent_before_get() function works. This function
  gets address of previous extent, by subtracting page size from current
  extent address. If current extent is located at PAGE_SIZE offset, this
  address resolved to 0x0000. An assertion in rtree_leaf_elm_lookup
  then caused the running program to abort.
  
  This problem was discovered when trying to build world on 32-bit
  machines with ASLR and PIE enabled. The problem was encountered
  on armv7 and i386 machines, but most likely other 32-bit
  architectures are affected as well.
  
  While this patch fixes one problem with buildworld on 32-bit platforms
  with ASLR, the build still fails, however it happens much later
  and due to lack of memory.
  
  The change is aligned with accepted fix in the upstream Jemalloc
  repository (https://github.com/jemalloc/jemalloc/pull/1973).
  As it doesn't apply on top of Jemalloc tree, its updated version
  was eventually merged: https://github.com/jemalloc/jemalloc/pull/2003
  
  PR: 249937
  Submitted by: Dawid Gorecki <dgr at semihalf.com>
  Obtained from: Semihalf
  Sponsored by: Stormshield
  Differential Revision: https://reviews.freebsd.org/D27025

Modified:
  head/contrib/jemalloc/src/extent.c

Modified: head/contrib/jemalloc/src/extent.c
==============================================================================
--- head/contrib/jemalloc/src/extent.c	Fri Dec 18 10:08:11 2020	(r368755)
+++ head/contrib/jemalloc/src/extent.c	Fri Dec 18 10:09:21 2020	(r368756)
@@ -1641,8 +1641,11 @@ extent_try_coalesce_impl(tsdn_t *tsdn, arena_t *arena,
 		}
 
 		/* Try to coalesce backward. */
-		extent_t *prev = extent_lock_from_addr(tsdn, rtree_ctx,
-		    extent_before_get(extent), inactive_only);
+		extent_t *prev = NULL;
+		if (extent_before_get(extent) != NULL) {
+			prev = extent_lock_from_addr(tsdn, rtree_ctx,
+			    extent_before_get(extent), inactive_only);
+		}
 		if (prev != NULL) {
 			bool can_coalesce = extent_can_coalesce(arena, extents,
 			    extent, prev);