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construct/ircd/db_fixes.cc

353 lines
8.1 KiB
C++

// The Construct
//
// Copyright (C) The Construct Developers, Authors & Contributors
// Copyright (C) 2016-2020 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.
/////////////////////////////////////////////////////////////////////////////////
//
// This unit exists to mitigate instances of bugs in RocksDB and its builds.
// It requires a complete copy of the rocksdb sourcecode to operate; though
// said source does not have to be built.
//
#define ROCKSDB_PLATFORM_POSIX
#define ZSTD_VERSION_NUMBER 0
#if __has_include("db/write_thread.h")
#include "db/write_thread.h"
#else
#error "RocksDB db/write_thread.h is not available. Cannot interpose bugfixes."
#endif
#if __has_include("util/file_util.h")
#include "util/file_util.h"
#elif __has_include("file/file_util.h")
#include "file/file_util.h"
#endif
#if __has_include("table/block_fetcher.h")
#include "table/block_fetcher.h"
#endif
#if __has_include("file/sst_file_manager_impl.h")
#include "file/sst_file_manager_impl.h"
#elif __has_include("util/sst_file_manager_impl.h")
#include "util/sst_file_manager_impl.h"
#else
#error "RocksDB file/sst_file_manager_imp.h is not available. Cannot interpose bugfixes."
#endif
#if __has_include("util/thread_local.h")
#include "util/thread_local.h"
#else
#error "RocksDB util/thread_local.h is not available. Cannot interpose bugfixes."
#endif
#if __has_include("table/block_based/reader_common.h")
#include "table/block_based/reader_common.h"
#endif
#include "db_has.h"
#include "db_env.h"
///////////////////////////////////////////////////////////////////////////////
//
// https://github.com/facebook/rocksdb/issues/4654. In summary, some RocksDB
// code makes direct use of std::mutex and std::condition_variable unlike the
// rest of RocksDB code which uses the rocksdb::port and rocksdb::Env wrapper
// interfaces. We have adapted the latter to work with ircd::ctx userspace
// threading (see: db_port.cc and db_env.cc), but the former is a direct
// interface to kernel pthreads which are incompatible in this context.
//
// Our mitigation is made possible by dynamic linking. It is a legitimate use
// of runtime interposition as stated in official documentation for this exact
// purpose: overriding buggy functions in library dependencies.
// This section overrides a class member function in rocksdb::WriteThread which
// originally made use of pthread primitives to handle two threads contending
// for write access in RocksDB's single-writer design. This function is entered
// by additional threads after a first thread is an established "write leader."
// These additional threads wait until a state bitmask satisfies them so they
// can continue. This waiting is accomplished with an std::condition_variable
// which tells the kernel to stop the thread until satisfied. Since we are not
// using kernel-driven threads, this is a deadlock.
//
#if __has_include("db/write_thread.h")
uint8_t
rocksdb::WriteThread::BlockingAwaitState(Writer *const w,
uint8_t goal_mask)
{
// Create the class member mutex and cv where it's expected by
// rocksdb callers
w->CreateMutex();
auto state(w->state.load(std::memory_order_acquire));
assert(state != STATE_LOCKED_WAITING);
if((state & goal_mask) == 0 && w->state.compare_exchange_strong(state, STATE_LOCKED_WAITING))
{
size_t yields(0);
while((state = w->state.load(std::memory_order_relaxed)) == STATE_LOCKED_WAITING)
{
ircd::ctx::yield();
++yields;
}
// Since we're using a coarse ctx::yield() it's theoretically possible
// that our loop can spin out of control. That is highly unlikely,
// and there is usually not even more than one iteration. Nevertheless
// we assert to be sure this is working within reason.
assert(yields < 32);
}
assert((state & goal_mask) != 0);
return state;
}
#endif
///////////////////////////////////////////////////////////////////////////////
//
// ThreadLocalPtr
//
#if __has_include("util/thread_local.h")
namespace ircd::db::fixes::tls
{
using key_pair = pair<uint32_t>;
static uint32_t id_ctr;
static std::map<uint64_t, void *> map;
static std::map<uint32_t, rocksdb::UnrefHandler> dtors;
static ctx::mutex dtor_mutex;
static key_pair make_key(const uint64_t &);
static uint64_t make_key(const key_pair &);
}
ircd::db::fixes::tls::key_pair
ircd::db::fixes::tls::make_key(const uint64_t &k)
{
return
{
uint32_t(k >> 32), uint32_t(k)
};
}
uint64_t
ircd::db::fixes::tls::make_key(const key_pair &k)
{
uint64_t ret(0UL);
ret |= k.first;
ret <<= 32;
ret |= k.second;
return ret;
}
void
rocksdb::ThreadLocalPtr::InitSingletons()
{
}
rocksdb::ThreadLocalPtr::ThreadLocalPtr(UnrefHandler handler)
:id_
{
uint32_t(ircd::db::fixes::tls::id_ctr++)
}
{
assert(ircd::db::fixes::tls::id_ctr < uint32_t(-1U));
if(handler)
{
using namespace ircd::db::fixes::tls;
const auto iit
{
dtors.emplace(id_, handler)
};
assert(iit.second);
}
}
rocksdb::ThreadLocalPtr::~ThreadLocalPtr()
{
using namespace ircd::db::fixes::tls;
const std::lock_guard lock
{
dtor_mutex
};
UnrefHandler dtor{nullptr};
{
const auto it
{
dtors.find(id_)
};
if(it != end(dtors))
{
dtor = it->second;
dtors.erase(it);
}
}
const uint64_t key[2]
{
make_key({id_, 0}), // lower bound
make_key({id_ + 1, 0}) // upper bound
};
auto it
{
map.lower_bound(key[0])
};
for(; it != end(map) && it->first < key[1]; it = map.erase(it))
if(dtor)
dtor(it->second);
}
void *
rocksdb::ThreadLocalPtr::Get()
const
{
using namespace ircd::db::fixes::tls;
const auto ctxid
{
ircd::ctx::current?
ircd::ctx::id():
0UL
};
const auto it
{
map.find(make_key({id_, ctxid}))
};
return it != end(map)?
it->second:
nullptr;
}
void
rocksdb::ThreadLocalPtr::Reset(void *const ptr)
{
this->Swap(ptr);
}
void *
rocksdb::ThreadLocalPtr::Swap(void *ptr)
{
using namespace ircd::db::fixes::tls;
const auto ctxid
{
ircd::ctx::current?
ircd::ctx::id():
0UL
};
const auto iit
{
map.emplace(make_key({id_, ctxid}), ptr)
};
if(iit.second)
return nullptr;
std::swap(iit.first->second, ptr);
return ptr;
}
bool
rocksdb::ThreadLocalPtr::CompareAndSwap(void *const ptr,
void *&expected)
{
using namespace ircd::db::fixes::tls;
const auto ctxid
{
ircd::ctx::current?
ircd::ctx::id():
0UL
};
const auto key
{
make_key({id_, ctxid})
};
const auto it
{
map.lower_bound(key)
};
if(it == end(map) || it->first != key)
{
if(expected != nullptr)
{
expected = nullptr;
return false;
}
map.emplace_hint(it, key, ptr);
return true;
}
if(it->second != expected)
{
expected = it->second;
return false;
}
it->second = ptr;
return true;
}
void
rocksdb::ThreadLocalPtr::Fold(FoldFunc func,
void *const res)
{
ircd::always_assert(false);
}
#endif
///////////////////////////////////////////////////////////////////////////////
//
// On platforms where hardware crc32 acceleration is not available and for
// use with valgrind, the crc32 checks over the data can be cumbersome. While
// rocksdb offers options in several places to disable checksum checking, these
// options are not honored in several places internally within rocksdb. Thus
// in case a developer wants to manually bypass the checksumming this stub is
// available.
//
#if defined(IRCD_DB_BYPASS_CHECKSUM) \
&& (__has_include("util/file_util.h") || __has_include("file/file_util.h") || __has_include("table/block_fetcher.h"))
void
rocksdb::BlockFetcher::CheckBlockChecksum()
{
//assert(false);
}
#endif
#if defined(IRCD_DB_BYPASS_CHECKSUM) \
&& __has_include("table/block_based/reader_common.h")
rocksdb::Status
rocksdb::VerifyBlockChecksum(ChecksumType type,
const char *const data,
size_t block_size,
const std::string& file_name,
uint64_t offset)
{
return Status::OK();
}
#endif