From 336dad2a07b17e46e5e81eab8a3209dffbbb928d Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Tue, 16 Aug 2016 22:05:57 -0400 Subject: [PATCH] runtime: fix check for vacuous page boundary rounding sysUnused (e.g., madvise MADV_FREE) is only sensible to call on physical page boundaries, so scavengelist rounds in the bounds of the region being released to the nearest physical page boundaries. However, if the region is smaller than a physical page and neither the start nor end fall on a boundary, then rounding the start up to a page boundary and the end down to a page boundary will result in end < start. Currently, we only give up on the region if start == end, so if we encounter end < start, we'll call madvise with a negative length and the madvise will fail. Issue #16644 gives a concrete example of this: start = 0x1285ac000 end = 0x1285ae000 (1 8K page) This leads to the rounded values start = 0x1285b0000 end = 0x1285a0000 which leads to len = -65536. Fix this by giving up on the region if end <= start, not just if end == start. Fixes #16644. Change-Id: I8300db492dbadc82ac1ad878318b36bcb7c39524 Reviewed-on: https://go-review.googlesource.com/27230 Reviewed-by: Keith Randall --- src/runtime/mheap.go | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go index db60f7a8727..3f873267ba3 100644 --- a/src/runtime/mheap.go +++ b/src/runtime/mheap.go @@ -917,7 +917,7 @@ func scavengelist(list *mSpanList, now, limit uint64) uintptr { // more memory than we want.) start = (start + sys.PhysPageSize - 1) &^ (sys.PhysPageSize - 1) end &^= sys.PhysPageSize - 1 - if start == end { + if start <= end { continue } }