diff --git a/compiler-rt/lib/asan/asan_linux.cc b/compiler-rt/lib/asan/asan_linux.cc
index 8ce4b96c26e..5cf466661f0 100644
--- a/compiler-rt/lib/asan/asan_linux.cc
+++ b/compiler-rt/lib/asan/asan_linux.cc
@@ -82,15 +82,27 @@ void *AsanDoesNotSupportStaticLinkage() {
   return &_DYNAMIC;  // defined in link.h
 }

+static void UnmapFromTo(uptr from, uptr to) {
+  CHECK(to >= from);
+  if (to == from) return;
+  uptr res = internal_munmap(reinterpret_cast<void *>(from), to - from);
+  if (UNLIKELY(internal_iserror(res))) {
+    Report(
+        "ERROR: AddresSanitizer failed to unmap 0x%zx (%zd) bytes at address "
+        "%p\n",
+        to - from, to - from, from);
+    CHECK("unable to unmap" && 0);
+  }
+}
+
 #if ASAN_PREMAP_SHADOW
 uptr FindPremappedShadowStart() {
   uptr granularity = GetMmapGranularity();
   uptr shadow_start = reinterpret_cast<uptr>(&__asan_shadow);
-  uptr shadow_size = PremapShadowSize();
-  UnmapOrDie((void *)(shadow_start - granularity), shadow_size + granularity);
-  // MmapNoAccess does not touch TotalMmap, but UnmapOrDie decreases it.
-  // Compensate.
-  IncreaseTotalMmap(shadow_size + granularity);
+  uptr premap_shadow_size = PremapShadowSize();
+  uptr shadow_size = RoundUpTo(kHighShadowEnd, granularity);
+  // We may have mapped too much. Release extra memory.
+  UnmapFromTo(shadow_start + shadow_size, shadow_start + premap_shadow_size);
   return shadow_start;
 }
 #endif
@@ -104,17 +116,15 @@ uptr FindDynamicShadowStart() {
   uptr granularity = GetMmapGranularity();
   uptr alignment = granularity * 8;
   uptr left_padding = granularity;
-  uptr shadow_size = kHighShadowEnd + left_padding;
-  uptr map_size = shadow_size + alignment;
+  uptr shadow_size = RoundUpTo(kHighShadowEnd, granularity);
+  uptr map_size = shadow_size + left_padding + alignment;

   uptr map_start = (uptr)MmapNoAccess(map_size);
   CHECK_NE(map_start, ~(uptr)0);

-  uptr shadow_start = RoundUpTo(map_start, alignment);
-  UnmapOrDie((void *)map_start, map_size);
-  // MmapNoAccess does not touch TotalMmap, but UnmapOrDie decreases it.
-  // Compensate.
-  IncreaseTotalMmap(map_size);
+  uptr shadow_start = RoundUpTo(map_start + left_padding, alignment);
+  UnmapFromTo(map_start, shadow_start - left_padding);
+  UnmapFromTo(shadow_start + shadow_size, map_start + map_size);

   return shadow_start;
 }
diff --git a/compiler-rt/lib/asan/asan_shadow_setup.cc b/compiler-rt/lib/asan/asan_shadow_setup.cc
index 08c009184f8..b3cf0b5c1ce 100644
--- a/compiler-rt/lib/asan/asan_shadow_setup.cc
+++ b/compiler-rt/lib/asan/asan_shadow_setup.cc
@@ -99,17 +99,21 @@ void InitializeShadowMemory() {
   // when necessary. When dynamic address is used, the macro |kLowShadowBeg|
   // expands to |__asan_shadow_memory_dynamic_address| which is
   // |kDefaultShadowSentinel|.
+  bool full_shadow_is_available = false;
   if (shadow_start == kDefaultShadowSentinel) {
     __asan_shadow_memory_dynamic_address = 0;
     CHECK_EQ(0, kLowShadowBeg);
     shadow_start = FindDynamicShadowStart();
+    if (SANITIZER_LINUX) full_shadow_is_available = true;
   }
   // Update the shadow memory address (potentially) used by instrumentation.
   __asan_shadow_memory_dynamic_address = shadow_start;

   if (kLowShadowBeg) shadow_start -= GetMmapGranularity();
-  bool full_shadow_is_available =
-      MemoryRangeIsAvailable(shadow_start, kHighShadowEnd);
+
+  if (!full_shadow_is_available)
+    full_shadow_is_available =
+        MemoryRangeIsAvailable(shadow_start, kHighShadowEnd);

 #if SANITIZER_LINUX && defined(__x86_64__) && defined(_LP64) && \
     !ASAN_FIXED_MAPPING