[compiler-rt] [scudo] Allow to resize allocation ring buffer (PR #82683)

[Florian Mayer via llvm-commits]

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@@ -1594,12 +1600,33 @@ class Allocator {
     RB->StackDepotSize = StackDepotSize;
     RB->RawStackDepotMap = DepotMap;
 
-    atomic_store(&RingBufferAddress, reinterpret_cast<uptr>(RB),
-                 memory_order_release);
+    swapOutRingBuffer(RB);
     static_assert(sizeof(AllocationRingBuffer) %
                           alignof(typename AllocationRingBuffer::Entry) ==
                       0,
                   "invalid alignment");
+    return true;
+  }
+
+  void swapOutRingBuffer(AllocationRingBuffer *NewRB) {
+    // To allow resizeRingBuffer to be called in a multi-threaded context by apps,
+    // we do not actually unmap, but only madvise(DONTNEED) the pages. That way,
+    // straggler threads will not crash.
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fmayer wrote:

I don't see how we would do this for apps. That would require all apps to call `malloc_set_track_allocation_stacks` themselves, otherwise they don't get any. Currently, the platform does this for them, but we wouldn't know whether we should do that, or the app wants to change the ring buffer size and thus call it itself.

https://github.com/llvm/llvm-project/pull/82683