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Fix locking and lifetime races in CLFUS compress_entries #13382

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Fix locking and lifetime races in CLFUS compress_entries #13382

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1 change: 1 addition & 0 deletions src/iocore/cache/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,7 @@ if(BUILD_TESTING)
add_cache_test(Update_Header unit_tests/test_Update_header.cc)
add_cache_test(CacheStripe unit_tests/test_Stripe.cc)
add_cache_test(CacheAggregateWriteBuffer unit_tests/test_AggregateWriteBuffer.cc)
add_cache_test(RamCacheCompressEntries unit_tests/test_RamCacheCompressEntries.cc)

# Unit Tests without unit_tests/main.cc
add_executable(test_ConfigVolumes unit_tests/test_ConfigVolumes.cc)
Expand Down
92 changes: 22 additions & 70 deletions src/iocore/cache/RamCacheCLFUS.cc
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Expand Up @@ -24,6 +24,7 @@
// Clocked Least Frequently Used by Size (CLFUS) replacement policy
// See https://cwiki.apache.org/confluence/display/TS/RamCache

#include "RamCacheCLFUS.h"
#include "P_RamCache.h"
#include "P_CacheInternal.h"
#include "StripeSM.h"
Expand Down Expand Up @@ -63,27 +64,6 @@ DbgCtl dbg_ctl_ram_cache_compare{"ram_cache_compare"};

#endif

struct RamCacheCLFUSEntry {
CryptoHash key;
uint64_t auxkey;
uint64_t hits;
uint32_t size; // memory used including padding in buffer
uint32_t len; // actual data length
uint32_t compressed_len;
union {
struct {
uint32_t compressed : 3; // compression type
uint32_t incompressible : 1;
uint32_t lru : 1;
uint32_t copy : 1; // copy-in-copy-out
} flag_bits;
uint32_t flags;
};
LINK(RamCacheCLFUSEntry, lru_link);
LINK(RamCacheCLFUSEntry, hash_link);
Ptr<IOBufferData> data;
};

constexpr uint64_t
requeue_hits(const uint64_t hits)
{
Expand All @@ -102,46 +82,6 @@ cache_value(const RamCacheCLFUSEntry *const e)
return cache_value_hits_size(e->hits, e->size);
}

class RamCacheCLFUS : public RamCache
{
public:
RamCacheCLFUS() {}

// returns 1 on found/stored, 0 on not found/stored, if provided auxkey1 and auxkey2 must match
int get(CryptoHash *key, Ptr<IOBufferData> *ret_data, uint64_t auxkey = 0) override;
int put(CryptoHash *key, IOBufferData *data, uint32_t len, bool copy = false, uint64_t auxkey = 0) override;
int fixup(const CryptoHash *key, uint64_t old_auxkey, uint64_t new_auxkey) override;
int64_t size() const override;

void init(int64_t max_bytes, StripeSM *stripe) override;

void compress_entries(EThread *thread, int do_at_most = INT_MAX);

// TODO move it to private.
StripeSM *stripe = nullptr; // for stats
private:
int64_t _max_bytes = 0;
int64_t _bytes = 0;
int64_t _objects = 0;

double _average_value = 0;
int64_t _history = 0;
int _ibuckets = 0;
int _nbuckets = 0;
DList(RamCacheCLFUSEntry, hash_link) *_bucket = nullptr;
Que(RamCacheCLFUSEntry, lru_link) _lru[2];
uint16_t *_seen = nullptr;
int _ncompressed = 0;
RamCacheCLFUSEntry *_compressed = nullptr; // first uncompressed lru[0] entry

void _resize_hashtable();
void _victimize(RamCacheCLFUSEntry *e);
void _move_compressed(RamCacheCLFUSEntry *e);
RamCacheCLFUSEntry *_destroy(RamCacheCLFUSEntry *e);
void _requeue_victims(Que(RamCacheCLFUSEntry, lru_link) & victims);
void _tick(); // move CLOCK on history
};

int64_t
RamCacheCLFUS::size() const
{
Expand Down Expand Up @@ -475,6 +415,12 @@ RamCacheCLFUS::compress_entries(EThread *thread, int do_at_most)
default:
goto Lcontinue;
case CACHE_COMPRESSION_FASTLZ:
if (e->len < 16) {
// fastlz cannot compress inputs this small; decide while the entry
// is still lock-protected rather than in the unlocked region below.
e->flag_bits.incompressible = 1;
goto Lcontinue;
}
l = static_cast<uint32_t>(static_cast<double>(e->len) * 1.05 + 66);
break;
case CACHE_COMPRESSION_LIBZ:
Expand All @@ -495,11 +441,11 @@ RamCacheCLFUS::compress_entries(EThread *thread, int do_at_most)
bool failed = false;
switch (ctype) {
default:
goto Lfailed;
// The bound switch above filtered unknown types; this is unreachable,
// but must not jump to Lfailed from this unlocked region.
failed = true;
break;
case CACHE_COMPRESSION_FASTLZ:
if (e->len < 16) {
goto Lfailed;
}
if ((l = fastlz_compress(edata->data(), elen, b)) <= 0) {
failed = true;
}
Expand All @@ -526,11 +472,10 @@ RamCacheCLFUS::compress_entries(EThread *thread, int do_at_most)
#endif
}
MUTEX_TAKE_LOCK(stripe->mutex, thread);
// see if the entry is till around
// See if the entry is still around; it may have been freed while the
// lock was dropped, so this must be checked before anything writes to
// it (including the failure marking below).
{
if (failed) {
goto Lfailed;
}
uint32_t i = key.slice32(3) % this->_nbuckets;
RamCacheCLFUSEntry *ee = this->_bucket[i].head;
while (ee) {
Expand All @@ -540,11 +485,18 @@ RamCacheCLFUS::compress_entries(EThread *thread, int do_at_most)
ee = ee->hash_link.next;
}
if (!ee || ee != e) {
e = this->_compressed;
ats_free(b);
e = this->_compressed;
if (!e) {
// The cursor was invalidated while the lock was dropped.
break;
}
goto Lcontinue;
}
}
if (failed) {
goto Lfailed;
}
if (l > required_compression * e->len) {
e->flag_bits.incompressible = true;
}
Expand Down
99 changes: 99 additions & 0 deletions src/iocore/cache/RamCacheCLFUS.h
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Original file line number Diff line number Diff line change
@@ -0,0 +1,99 @@
/** @file

Clocked Least Frequently Used by Size (CLFUS) RAM cache replacement policy.

@section license License

Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

#pragma once

// See https://cwiki.apache.org/confluence/display/TS/RamCache

#include "P_RamCache.h"

#include "iocore/eventsystem/IOBuffer.h"
#include "tscore/CryptoHash.h"
#include "tscore/List.h"

#include <climits>
#include <cstdint>

class EThread;
class StripeSM;

struct RamCacheCLFUSEntry {
CryptoHash key;
uint64_t auxkey;
uint64_t hits;
uint32_t size; // memory used including padding in buffer
uint32_t len; // actual data length
uint32_t compressed_len;
union {
struct {
uint32_t compressed : 3; // compression type
uint32_t incompressible : 1;
uint32_t lru : 1;
uint32_t copy : 1; // copy-in-copy-out
} flag_bits;
uint32_t flags;
};
LINK(RamCacheCLFUSEntry, lru_link);
LINK(RamCacheCLFUSEntry, hash_link);
Ptr<IOBufferData> data;
};

class RamCacheCLFUS : public RamCache
{
public:
RamCacheCLFUS() {}

// returns 1 on found/stored, 0 on not found/stored, if provided auxkey1 and auxkey2 must match
int get(CryptoHash *key, Ptr<IOBufferData> *ret_data, uint64_t auxkey = 0) override;
int put(CryptoHash *key, IOBufferData *data, uint32_t len, bool copy = false, uint64_t auxkey = 0) override;
int fixup(const CryptoHash *key, uint64_t old_auxkey, uint64_t new_auxkey) override;
int64_t size() const override;

void init(int64_t max_bytes, StripeSM *stripe) override;

void compress_entries(EThread *thread, int do_at_most = INT_MAX);

// TODO move it to private.
StripeSM *stripe = nullptr; // for stats
private:
int64_t _max_bytes = 0;
int64_t _bytes = 0;
int64_t _objects = 0;

double _average_value = 0;
int64_t _history = 0;
int _ibuckets = 0;
int _nbuckets = 0;
DList(RamCacheCLFUSEntry, hash_link) *_bucket = nullptr;
Que(RamCacheCLFUSEntry, lru_link) _lru[2];
uint16_t *_seen = nullptr;
int _ncompressed = 0;
RamCacheCLFUSEntry *_compressed = nullptr; // first uncompressed lru[0] entry

void _resize_hashtable();
void _victimize(RamCacheCLFUSEntry *e);
void _move_compressed(RamCacheCLFUSEntry *e);
RamCacheCLFUSEntry *_destroy(RamCacheCLFUSEntry *e);
void _requeue_victims(Que(RamCacheCLFUSEntry, lru_link) & victims);
void _tick(); // move CLOCK on history
};
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