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[release/7.0] Fix race condition in DacEnumerableHashTable::BaseFindNextEntryByHash #75178

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merged 3 commits into from
Sep 7, 2022
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[release/7.0] Fix race condition in DacEnumerableHashTable::BaseFindNextEntryByHash #75178

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badbd98
Fix race condition in DacEnumerableHashTable::BaseFindNextEntryByHash
AntonLapounov Sep 6, 2022
aeeb77e
Use a volatile load
AntonLapounov Sep 6, 2022
e6367bc
One more volatile load
AntonLapounov Sep 6, 2022
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16 changes: 7 additions & 9 deletions src/coreclr/vm/dacenumerablehash.inl
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Original file line number Diff line number Diff line change
Expand Up @@ -309,8 +309,8 @@ DPTR(VALUE) DacEnumerableHashTable<DAC_ENUM_HASH_ARGS>::BaseFindFirstEntryByHash
// +2 to skip "length" and "next" slots
DWORD dwBucket = iHash % cBuckets + SKIP_SPECIAL_SLOTS;

// Point at the first entry in the bucket chain which would contain any entries with the given hash code.
PTR_VolatileEntry pEntry = curBuckets[dwBucket];
// Point at the first entry in the bucket chain that stores entries with the given hash code.
PTR_VolatileEntry pEntry = VolatileLoadWithoutBarrier(&curBuckets[dwBucket]);

// Walk the bucket chain one entry at a time.
while (pEntry)
Expand All @@ -329,13 +329,13 @@ DPTR(VALUE) DacEnumerableHashTable<DAC_ENUM_HASH_ARGS>::BaseFindFirstEntryByHash
}

// Move to the next entry in the chain.
pEntry = pEntry->m_pNextEntry;
pEntry = VolatileLoadWithoutBarrier(&pEntry->m_pNextEntry);
}

// in a rare case if resize is in progress, look in the new table as well.
// if existing entry is not in the old table, it must be in the new
// since we unlink it from old only after linking into the new.
// check for next table must hapen after we looked through the current.
// check for next table must happen after we looked through the current.
VolatileLoadBarrier();
curBuckets = GetNext(curBuckets);
} while (curBuckets != nullptr);
Expand Down Expand Up @@ -367,11 +367,9 @@ DPTR(VALUE) DacEnumerableHashTable<DAC_ENUM_HASH_ARGS>::BaseFindNextEntryByHash(
PTR_VolatileEntry pVolatileEntry = dac_cast<PTR_VolatileEntry>(pContext->m_pEntry);
iHash = pVolatileEntry->m_iHashValue;

// Iterate over the bucket chain.
while (pVolatileEntry->m_pNextEntry)
// Iterate over the rest ot the bucket chain.
while ((pVolatileEntry = VolatileLoadWithoutBarrier(&pVolatileEntry->m_pNextEntry)) != nullptr)
{
// Advance to the next entry.
pVolatileEntry = pVolatileEntry->m_pNextEntry;
if (pVolatileEntry->m_iHashValue == iHash)
{
// Found a match on hash code. Update our find context to indicate where we got to and return
Expand All @@ -381,7 +379,7 @@ DPTR(VALUE) DacEnumerableHashTable<DAC_ENUM_HASH_ARGS>::BaseFindNextEntryByHash(
}
}

// check for next table must hapen after we looked through the current.
// check for next table must happen after we looked through the current.
VolatileLoadBarrier();

// in a case if resize is in progress, look in the new table as well.
Expand Down