test case for acquire race

cachelib/CMakeLists.txt

@@ -396,4 +396,10 @@ if (BUILD_TESTS)
     RENAME
       Makefile
   )
+  install(
+    FILES
+      ${CACHELIB_HOME}/allocator/tests/ChainedItemParentAcquireAfterMove.gdb
+    DESTINATION
+      ${TESTS_INSTALL_DIR}
+  )
 endif()

cachelib/allocator/tests/AllocatorTypeTest.cpp

@@ -292,6 +292,10 @@ TYPED_TEST(BaseAllocatorTest, TransferChainAfterMoving) {
   this->testTransferChainAfterMoving();
 }
 
+TYPED_TEST(BaseAllocatorTest, ChainedItemParentAcquireAfterMove) {
+  this->testChainedItemParentAcquireAfterMove();
+}
+
 TYPED_TEST(BaseAllocatorTest, AddAndPopChainedItemMultithread) {
   this->testAddAndPopChainedItemMultithread();
 }

cachelib/allocator/tests/BaseAllocatorTest.h

@@ -19,6 +19,12 @@
 #include <folly/Random.h>
 #include <folly/Singleton.h>
 #include <folly/synchronization/Baton.h>
+#include <folly/synchronization/Latch.h>
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <ctype.h>
+#include <semaphore.h>
 
 #include <algorithm>
 #include <chrono>
@@ -5189,6 +5195,152 @@ class BaseAllocatorTest : public AllocatorTest<AllocatorT> {
     }
   }
 
+  // helper function to check if gdb is running and attached to test
+  bool isGdbAttached() {
+    char buf[4096];
+    const int status_fd = open("/proc/self/status", O_RDONLY);
+    if (status_fd == -1) {
+      return false;
+    }
+    const ssize_t num_read = read(status_fd, buf, sizeof(buf) - 1);
+    close(status_fd);
+
+    if (num_read <= 0) {
+      return false;
+    }
+    buf[num_read] = '\0';
+    constexpr char tracerPidString[] = "TracerPid:";
+    const auto tracer_pid_ptr = strstr(buf, tracerPidString);
+    if (!tracer_pid_ptr) {
+      return false;
+    }
+    for (const char* characterPtr = tracer_pid_ptr + sizeof(tracerPidString) - 1; 
+            characterPtr <= buf + num_read; ++characterPtr) {
+      if (isspace(*characterPtr)) {
+        continue;
+      } else {
+        return isdigit(*characterPtr) != 0 && *characterPtr != '0';
+      }
+    }
+    return false;
+  }
+
+  void gdb_sync1() { sleep(1); }
+  void gdb_sync2() { sleep(1); }
+  void gdb_sync3() { sleep(1); }
+  void gdb_sync4() { sleep(1); }
+  void testChainedItemParentAcquireAfterMove() {
+    sem_unlink("/gdb1_sem");
+    sem_t *sem = sem_open("/gdb1_sem", O_CREAT | O_EXCL, S_IRUSR | S_IWUSR, 0);
+    int ppid = getpid(); //parent pid
+    int fpid = fork();
+    if (fpid == 0) {
+        sem_wait(sem);
+        sem_close(sem);
+        sem_unlink("/gdb1_sem");
+        char cmdpid[256];
+        sprintf(cmdpid,"%d",ppid);
+        int f = execlp("gdb","gdb","--pid",cmdpid,
+                "--batch-silent","--command=ChainedItemParentAcquireAfterMove.gdb",(char*) 0);
+        ASSERT(f != -1);
+    }
+
+    // create an allocator worth 4 slabs 
+    // first slab is for overhead, second is parent class
+    // thrid is chained item 1 and fourth is for new chained item alloc
+    // to move to.
+    typename AllocatorT::Config config;
+    config.configureChainedItems();
+
+    config.setCacheSize(4 * Slab::kSize);
+
+    using Item = typename AllocatorT::Item;
+
+    std::atomic<uint64_t> numRemovedKeys{0};
+    config.setRemoveCallback(
+        [&](const typename AllocatorT::RemoveCbData&) { ++numRemovedKeys; });
+
+    std::atomic<uint64_t> numMoves{0};
+    config.enableMovingOnSlabRelease(
+        [&](Item& oldItem, Item& newItem, Item* /* parentPtr */) {
+          assert(oldItem.getSize() == newItem.getSize());
+          assert(oldItem.isChainedItem());
+          std::memcpy(newItem.getMemory(), oldItem.getMemory(),
+                      oldItem.getSize());
+          ++numMoves;
+        }
+    );
+
+    AllocatorT alloc(config);
+    const size_t numBytes = alloc.getCacheMemoryStats().ramCacheSize;
+    const auto poolSize = numBytes;
+    //items are 100K and 200K
+    const std::set<uint32_t> allocSizes = {2*1024*1024 + 1024 , 3*1024*1024};
+    const auto pid = alloc.addPool("one", poolSize, allocSizes);
+
+    // Allocate 1 parent items and for each parent item, 1 chained
+    // allocation
+    auto allocFn = [&](std::string keyPrefix, std::vector<uint32_t> sizes) {
+      for (unsigned int loop = 0; loop < 1; ++loop) {
+        std::vector<uint8_t*> bufList;
+        std::vector<typename AllocatorT::WriteHandle> parentHandles;
+        for (unsigned int i = 0; i < 1; ++i) {
+          const auto key = keyPrefix + folly::to<std::string>(loop) + "_" +
+                           folly::to<std::string>(i);
+
+          auto itemHandle = util::allocateAccessible(alloc, pid, key, sizes[0]);
+
+          for (unsigned int j = 0; j < 1; ++j) {
+            auto childItem =
+                alloc.allocateChainedItem(itemHandle, sizes[1]);
+            ASSERT_NE(nullptr, childItem);
+
+            uint8_t* buf = reinterpret_cast<uint8_t*>(childItem->getMemory());
+            // write first 50 bytes here
+            for (uint8_t k = 0; k < 50; ++k) {
+              buf[k] = k;
+            }
+            bufList.push_back(buf);
+
+            alloc.addChainedItem(itemHandle, std::move(childItem));
+          }
+        }
+      }
+    };
+    auto sizes = std::vector<uint32_t>{2*1024*1024, 3*1024*1024 - 1000};
+    allocFn(std::string{"yolo"}, sizes);
+
+    sem_post(sem);
+    while (!isGdbAttached()) {
+      std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    }
+    //need to suspend thread 1 - who is doing the eviction
+    //gdb will do this for us
+    folly::Latch latch(1);
+    std::unique_ptr<std::thread> r = std::make_unique<std::thread>([&](){
+      ClassId cid = static_cast<ClassId>(1);
+      //gdb will interupt this thread when we hit acquire
+      //we will then switch to the other thread and attempt 
+      //to evict the parent
+      gdb_sync1();
+      latch.count_down();
+      alloc.releaseSlab(pid, cid, SlabReleaseMode::kRebalance);
+      gdb_sync3();
+    });
+    r->detach();
+
+    latch.wait();
+    //this alloc should fail because item can't be marked for eviction
+    //and we exceed evict attempts
+    auto itemHandle = util::allocateAccessible(alloc, pid, std::to_string(10), sizes[0]);
+    EXPECT_EQ(itemHandle, nullptr);
+    //complete the move
+    gdb_sync2();
+    auto itemHandle2 = util::allocateAccessible(alloc, pid, std::to_string(11), sizes[0]);
+    EXPECT_NE(itemHandle2, nullptr);
+    gdb_sync4();
+
+  }
   // Test stats on counting chained items
   // 1. Alloc an item and several chained items
   //    * Before inserting chained items, make sure count is zero

cachelib/allocator/tests/ChainedItemParentAcquireAfterMove.gdb

@@ -0,0 +1,22 @@
+break gdb_sync1
+c
+set scheduler-locking on
+break acquire
+c
+c
+c
+c
+thread 1
+set scheduler-locking on
+del 2
+break gdb_sync2
+c
+thread 4
+set scheduler-locking on
+break gdb_sync3
+c
+thread 1
+set scheduler-locking off
+break gdb_sync4
+c
+c