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[wasm] Add missing scopes for code modification
This is the second CL in a line of two (see crrev.com/c/2835237) to bring write-protection to the WebAssembly code space. The previous CL changed the page permissions from W^X (only either writable or executable can be active, but never both) to write-protection (due to concurrent execution in the main thread). However, write-protection still did not work, because in several places the code space is modified without properly switching it to writable beforehand. This CL fixes --wasm-write-protect-code-memory such that it can now be enabled again (with potentially high overhead due to frequent page protection switches). For that, it adds the missing switching to writable by adding {NativeModuleModificationScope} objects (similar to the already existing {CodeSpaceWriteScope} objects for Apple M1 hardware). This CL also fixes a race condition between checking for the current writable permission and actually setting the permission, by protecting the counter of currently active writers with the same lock as the {WasmCodeAllocator} itself. (Before multi-threaded compilation, this was not necessary.) Finally, this CL also changes the {Mutex} protecting the {WasmCodeAllocator} to a {RecursiveMutex} because it can be requested multiple times in the call hierarchy of the same thread, which would cause a deadlock otherwise. Since {TryLock()} of a {RecursiveMutex} never fails, this also removes the (now failing) DCHECKs. R=clemensb@chromium.org CC=​​jkummerow@chromium.org Bug: v8:11663 Change-Id: I4db27ad0a9348021b0b663dbe88b3432a4d8d6b5 Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel_ng Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2835238 Commit-Queue: Daniel Lehmann <dlehmann@google.com> Reviewed-by: Clemens Backes <clemensb@chromium.org> Cr-Commit-Position: refs/heads/master@{#74163}
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‎src/base/platform/mutex.h‎

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@@ -164,6 +164,8 @@ class V8_BASE_EXPORT RecursiveMutex final {
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// successfully locked.
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bool TryLock() V8_WARN_UNUSED_RESULT;
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V8_INLINE void AssertHeld() const { DCHECK_LT(0, level_); }
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private:
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// The implementation-defined native handle type.
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#if V8_OS_POSIX

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