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fix(runtime): remove /dev/shm mmap file immediately after open #425

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Merged
zoowii merged 3 commits into from
Mar 27, 2026
Merged

fix(runtime): remove /dev/shm mmap file immediately after open #425

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b58defb
fix(runtime): remove /dev/shm mmap file immediately after open
cmgCr Mar 20, 2026
ad7ae0a
fix(compiler): disable mmap-bucket on early-unlink failure
cmgCr Mar 20, 2026
9799750
fix(runtime): use -1 as invalid fd sentinel for MmapMemoryInitFd
cmgCr Mar 27, 2026
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26 changes: 18 additions & 8 deletions src/runtime/memory.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,22 @@ WasmMemoryAllocator::WasmMemoryAllocator(
Stats.revertRecord(Timer);
goto try_use_mmap_init;
}
// Remove the directory entry while keeping the fd open. On POSIX,
// remove() on a regular file is equivalent to unlink(): it deletes the
// name from the filesystem but the file data remains accessible through
// any open fd or mmap. The kernel reclaims the storage automatically
// when the last fd/mmap reference is closed — even on abnormal exit
// (SIGKILL, crash). This prevents /dev/shm file accumulation.
if (::remove(Path) != 0) {
ZEN_LOG_WARN("failed to early-unlink mmap file %s due to '%s', "
"disabling mmap-bucket for this module",
Path, std::strerror(errno));
::close(MmapFileFd);
MmapFileFd = -1;
UseMmapBucket = false;
Stats.revertRecord(Timer);
goto try_use_mmap_init;
}
MmapMemoryFilepath = ::strdup(Path);
DefaultMemoryType = WM_MEMORY_DATA_TYPE_BUCKET_MMAP;
MmapMemoryBucketGrowMaxSize = MmapMemoryFileMaxSize;
Expand Down Expand Up @@ -181,14 +197,8 @@ WasmMemoryAllocator::~WasmMemoryAllocator() {
}
delete MmapAddresses;
}
if (MmapMemoryInitFd > 0) {
if (MmapMemoryInitFd >= 0) {
::close(MmapMemoryInitFd);
// delete the memory file forcely
int Status = ::remove(MmapMemoryFilepath);
if (Status != 0) {
ZEN_LOG_WARN("failed to remove mmap tmp memory file %s due to '%s'",
MmapMemoryFilepath, std::strerror(errno));
}
}
Comment on lines 199 to 202
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Copilot AI Mar 23, 2026

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MmapMemoryInitFd uses 0 as the “invalid” sentinel, and the destructor (and checkWasmMemoryCanUseMmap()) only close/accept the fd when > 0. Since POSIX open() can legally return fd 0 (e.g., if stdin is closed), this can leak the fd and—now that the file is unlinked—prevent tmpfs storage from being reclaimed until process exit. Use -1 as the sentinel and treat >= 0 as valid in both the close and the checkWasmMemoryCanUseMmap() logic.

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@cmgCr cmgCr Mar 27, 2026

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update in new commit 9799750

if (MmapMemoryFilepath) {
::free(MmapMemoryFilepath);
Expand All @@ -206,7 +216,7 @@ bool WasmMemoryAllocator::checkWasmMemoryCanUseMmap() {
bool CanUseMmap = false;
if (UseMmap) {
if (DefaultMemoryType == WM_MEMORY_DATA_TYPE_BUCKET_MMAP &&
MmapMemoryInitFd > 0) {
MmapMemoryInitFd >= 0) {
CanUseMmap = true;
}
}
Expand Down
2 changes: 1 addition & 1 deletion src/runtime/memory.h
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Expand Up @@ -125,7 +125,7 @@ class WasmMemoryAllocator {
// when grow to not larger then it, just inc the size.
// otherwise mmap another copy and copy data
size_t MmapMemoryBucketGrowMaxSize = 0;
int MmapMemoryInitFd = 0; // when <=0, means not create memory file
int MmapMemoryInitFd = -1; // when <0, means not create memory file
char *MmapMemoryFilepath = nullptr;
// use pointers so when MMAP_BUCKET enabled but the module has no memory,
// then no need to create the objects
Expand Down
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