glibc-RHEL-21884.patch

commit 85860ad6eaf4c9739318f6b2a1ff7c2fa6b12ab5
Author: Florian Weimer <fweimer@redhat.com>
Date:   Mon Aug 15 16:45:40 2022 +0200

    malloc: Do not use MAP_NORESERVE to allocate heap segments
    
    Address space for heap segments is reserved in a mmap call with
    MAP_ANONYMOUS | MAP_PRIVATE and protection flags PROT_NONE.  This
    reservation does not count against the RSS limit of the process or
    system.  Backing memory is allocated using mprotect in alloc_new_heap
    and grow_heap, and at this point, the allocator expects the kernel
    to provide memory (subject to memory overcommit).
    
    The SIGSEGV that might generate due to MAP_NORESERVE (according to
    the mmap manual page) does not seem to occur in practice, it's always
    SIGKILL from the OOM killer.  Even if there is a way that SIGSEGV
    could be generated, it is confusing to applications that this only
    happens for secondary heaps, not for large mmap-based allocations,
    and not for the main arena.
    
    Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

Conflicts:
	malloc/arena.c
	(huge page support was added upstream)

diff --git a/malloc/arena.c b/malloc/arena.c
index 667484630ed0afa5..2852783355d3d869 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -466,8 +466,7 @@ new_heap (size_t size, size_t top_pad)
   p2 = MAP_FAILED;
   if (aligned_heap_area)
     {
-      p2 = (char *) MMAP (aligned_heap_area, HEAP_MAX_SIZE, PROT_NONE,
-                          MAP_NORESERVE);
+      p2 = (char *) MMAP (aligned_heap_area, HEAP_MAX_SIZE, PROT_NONE, 0);
       aligned_heap_area = NULL;
       if (p2 != MAP_FAILED && ((unsigned long) p2 & (HEAP_MAX_SIZE - 1)))
         {
@@ -477,7 +476,7 @@ new_heap (size_t size, size_t top_pad)
     }
   if (p2 == MAP_FAILED)
     {
-      p1 = (char *) MMAP (0, HEAP_MAX_SIZE << 1, PROT_NONE, MAP_NORESERVE);
+      p1 = (char *) MMAP (0, HEAP_MAX_SIZE << 1, PROT_NONE, 0);
       if (p1 != MAP_FAILED)
         {
           p2 = (char *) (((unsigned long) p1 + (HEAP_MAX_SIZE - 1))
@@ -493,7 +492,7 @@ new_heap (size_t size, size_t top_pad)
         {
           /* Try to take the chance that an allocation of only HEAP_MAX_SIZE
              is already aligned. */
-          p2 = (char *) MMAP (0, HEAP_MAX_SIZE, PROT_NONE, MAP_NORESERVE);
+          p2 = (char *) MMAP (0, HEAP_MAX_SIZE, PROT_NONE, 0);
           if (p2 == MAP_FAILED)
             return 0;
 
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 375f50f5db13e234..fe80b8239756a7c9 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -1112,10 +1112,6 @@ static mchunkptr mremap_chunk(mchunkptr p, size_t new_size);
 # define MAP_ANONYMOUS MAP_ANON
 #endif
 
-#ifndef MAP_NORESERVE
-# define MAP_NORESERVE 0
-#endif
-
 #define MMAP(addr, size, prot, flags) \
  __mmap((addr), (size), (prot), (flags)|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0)