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MCOL-5487 Managed shmem segment access/remap race

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There is a potential edge case when a thread remaps EM
    managed shmem segment in grabEMEntryTable() whilst another
    thread access the current shmem segment mapping in virtual memory
This commit is contained in:
Roman Nozdrin
2023-04-26 17:36:21 +00:00
parent 445eb75e4f
commit eab91b5022
2 changed files with 23 additions and 6 deletions
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24
versioning/BRM/extentmap.cpp
View File

@@ -219,7 +219,9 @@ boost::mutex ExtentMapRBTreeImpl::fInstanceMutex;
ExtentMapRBTreeImpl* ExtentMapRBTreeImpl::fInstance = nullptr; ExtentMapRBTreeImpl* ExtentMapRBTreeImpl::fInstance = nullptr;
/*static*/ /*static*/
ExtentMapRBTreeImpl* ExtentMapRBTreeImpl::makeExtentMapRBTreeImpl(unsigned key, off_t size, bool readOnly) ExtentMapRBTreeImpl* ExtentMapRBTreeImpl::makeExtentMapRBTreeImpl(unsigned key, off_t size, bool readOnly,
bool& emLocked,
const MasterSegmentTable* emSegTable)
{ {
boost::mutex::scoped_lock lk(fInstanceMutex); boost::mutex::scoped_lock lk(fInstanceMutex);
@@ -227,7 +229,17 @@ ExtentMapRBTreeImpl* ExtentMapRBTreeImpl::makeExtentMapRBTreeImpl(unsigned key,
{ {
if (key != fInstance->fManagedShm.key()) if (key != fInstance->fManagedShm.key())
{ {
if (emSegTable)
{
emSegTable->getTable_upgrade(MasterSegmentTable::EMTable);
emLocked = true;
}
fInstance->fManagedShm.reMapSegment(); fInstance->fManagedShm.reMapSegment();
if (emSegTable)
{
emLocked = false;
emSegTable->getTable_downgrade(MasterSegmentTable::EMTable);
}
} }
return fInstance; return fInstance;
@@ -1941,7 +1953,11 @@ void ExtentMap::grabEMEntryTable(OPS op)
} }
else else
{ {
fPExtMapRBTreeImpl = ExtentMapRBTreeImpl::makeExtentMapRBTreeImpl(fEMRBTreeShminfo->tableShmkey, 0); const bool isReadOnly = false;
// The ternary sends EM segment table only if this grabEMEntryTable call
// is for a READ op to enable RWLock upgrade in case of a shmem segment remap.
fPExtMapRBTreeImpl = ExtentMapRBTreeImpl::makeExtentMapRBTreeImpl(
fEMRBTreeShminfo->tableShmkey, 0, isReadOnly, emLocked, op == READ ? &fMST : nullptr);
ASSERT(fPExtMapRBTreeImpl); ASSERT(fPExtMapRBTreeImpl);
fExtentMapRBTree = fPExtMapRBTreeImpl->get(); fExtentMapRBTree = fPExtMapRBTreeImpl->get();
@@ -2176,8 +2192,8 @@ void ExtentMap::growEMShmseg(size_t size)
if (fEMRBTreeShminfo->tableShmkey == 0) if (fEMRBTreeShminfo->tableShmkey == 0)
fEMRBTreeShminfo->tableShmkey = newShmKey; fEMRBTreeShminfo->tableShmkey = newShmKey;
fPExtMapRBTreeImpl = fPExtMapRBTreeImpl = ExtentMapRBTreeImpl::makeExtentMapRBTreeImpl(fEMRBTreeShminfo->tableShmkey,
ExtentMapRBTreeImpl::makeExtentMapRBTreeImpl(fEMRBTreeShminfo->tableShmkey, allocSize, r_only); allocSize, r_only, emLocked);
} }
else else
{ {

5
versioning/BRM/extentmap.h
View File

@@ -34,7 +34,7 @@
#include <tr1/unordered_map> #include <tr1/unordered_map>
#include <mutex> #include <mutex>
//#define NDEBUG // #define NDEBUG
#include <cassert> #include <cassert>
#include <boost/functional/hash.hpp> //boost::hash #include <boost/functional/hash.hpp> //boost::hash
#include <boost/interprocess/allocators/allocator.hpp> #include <boost/interprocess/allocators/allocator.hpp>
@@ -253,7 +253,8 @@ class ExtentMapRBTreeImpl
public: public:
~ExtentMapRBTreeImpl() = default; ~ExtentMapRBTreeImpl() = default;
static ExtentMapRBTreeImpl* makeExtentMapRBTreeImpl(unsigned key, off_t size, bool readOnly = false); static ExtentMapRBTreeImpl* makeExtentMapRBTreeImpl(unsigned key, off_t size, bool readOnly, bool& emLocked,
const MasterSegmentTable* emSegTable = nullptr);
static void refreshShm() static void refreshShm()
{ {