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74 lines
2.8 KiB
74 lines
2.8 KiB
1 month ago
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commit 85860ad6eaf4c9739318f6b2a1ff7c2fa6b12ab5
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Mon Aug 15 16:45:40 2022 +0200
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malloc: Do not use MAP_NORESERVE to allocate heap segments
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Address space for heap segments is reserved in a mmap call with
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MAP_ANONYMOUS | MAP_PRIVATE and protection flags PROT_NONE. This
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reservation does not count against the RSS limit of the process or
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system. Backing memory is allocated using mprotect in alloc_new_heap
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and grow_heap, and at this point, the allocator expects the kernel
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to provide memory (subject to memory overcommit).
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The SIGSEGV that might generate due to MAP_NORESERVE (according to
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the mmap manual page) does not seem to occur in practice, it's always
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SIGKILL from the OOM killer. Even if there is a way that SIGSEGV
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could be generated, it is confusing to applications that this only
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happens for secondary heaps, not for large mmap-based allocations,
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and not for the main arena.
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Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
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Conflicts:
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malloc/arena.c
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(huge page support was added upstream)
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diff --git a/malloc/arena.c b/malloc/arena.c
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index 667484630ed0afa5..2852783355d3d869 100644
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--- a/malloc/arena.c
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+++ b/malloc/arena.c
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@@ -466,8 +466,7 @@ new_heap (size_t size, size_t top_pad)
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p2 = MAP_FAILED;
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if (aligned_heap_area)
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{
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- p2 = (char *) MMAP (aligned_heap_area, HEAP_MAX_SIZE, PROT_NONE,
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- MAP_NORESERVE);
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+ p2 = (char *) MMAP (aligned_heap_area, HEAP_MAX_SIZE, PROT_NONE, 0);
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aligned_heap_area = NULL;
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if (p2 != MAP_FAILED && ((unsigned long) p2 & (HEAP_MAX_SIZE - 1)))
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{
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@@ -477,7 +476,7 @@ new_heap (size_t size, size_t top_pad)
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}
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if (p2 == MAP_FAILED)
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{
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- p1 = (char *) MMAP (0, HEAP_MAX_SIZE << 1, PROT_NONE, MAP_NORESERVE);
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+ p1 = (char *) MMAP (0, HEAP_MAX_SIZE << 1, PROT_NONE, 0);
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if (p1 != MAP_FAILED)
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{
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p2 = (char *) (((unsigned long) p1 + (HEAP_MAX_SIZE - 1))
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@@ -493,7 +492,7 @@ new_heap (size_t size, size_t top_pad)
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{
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/* Try to take the chance that an allocation of only HEAP_MAX_SIZE
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is already aligned. */
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- p2 = (char *) MMAP (0, HEAP_MAX_SIZE, PROT_NONE, MAP_NORESERVE);
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+ p2 = (char *) MMAP (0, HEAP_MAX_SIZE, PROT_NONE, 0);
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if (p2 == MAP_FAILED)
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return 0;
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diff --git a/malloc/malloc.c b/malloc/malloc.c
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index 375f50f5db13e234..fe80b8239756a7c9 100644
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--- a/malloc/malloc.c
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+++ b/malloc/malloc.c
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@@ -1112,10 +1112,6 @@ static mchunkptr mremap_chunk(mchunkptr p, size_t new_size);
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# define MAP_ANONYMOUS MAP_ANON
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#endif
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-#ifndef MAP_NORESERVE
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-# define MAP_NORESERVE 0
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-#endif
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-
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#define MMAP(addr, size, prot, flags) \
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__mmap((addr), (size), (prot), (flags)|MAP_ANONYMOUS|MAP_PRIVATE, -1, 0)
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