Fix serious FSDirectory use-after-Close bug (missing fsync) (facebook…

…#10460)

Summary:
TL;DR: due to a recent change, if you drop a column family,
often that DB will no longer fsync after writing new SST files
to remaining or new column families, which could lead to data
loss on power loss.

More bug detail:
The intent of facebook#10049 was to Close FSDirectory objects at
DB::Close time rather than waiting for DB object destruction.
Unfortunately, it also closes shared FSDirectory objects on
DropColumnFamily (& destroy remaining handles), which can lead
to use-after-Close on FSDirectory shared with remaining column
families. Those "uses" are only Fsyncs (or redundant Closes). In
the default Posix filesystem, an Fsync on a closed FSDirectory is a
quiet no-op. Consequently (under most configurations), if you drop
a column family, that DB will no longer fsync after writing new SST
files to column families sharing the same directory (true under most
configurations).

More fix detail:
Basically, this removes unnecessary Close ops on destroying
ColumnFamilyData. We let `shared_ptr` take care of calling the
destructor at the right time. If the intent was to require Close be
called before destroying FSDirectory, that was not made clear by the
author of FileSystem and was not at all enforced by facebook#10049, which
could have added `assert(fd_ == -1)` to `~PosixDirectory()` but did
not. To keep this fix simple, we relax the unit test for facebook#10049 to allow
timely destruction of FSDirectory to suffice as Close (in
CountedFileSystem). Added a TODO to revisit that.

Also in this PR:
* Added a TODO to share FSDirectory instances between DB and its column
families. (Already shared among column families.)
* Made DB::Close attempt to close all its open FSDirectory objects even
if there is a failure in closing one. Also code clean-up around this
logic.

Pull Request resolved: facebook#10460

Test Plan:
add an assert to check for use-after-Close. With that
existing tests can detect the misuse. With fix, tests pass (except noted
relaxing of unit test for facebook#10049)

Reviewed By: ajkr

Differential Revision: D38357922

Pulled By: pdillinger

fbshipit-source-id: d42079cadbedf0a969f03389bf586b3b4e1f9137

HISTORY.md

@@ -13,6 +13,7 @@
 * `CompactRangeOptions::exclusive_manual_compaction` is now false by default. This ensures RocksDB does not introduce artificial parallelism limitations by default.
 
 ### Bug Fixes
+* Fix a bug starting in 7.4.0 in which some fsync operations might be skipped in a DB after any DropColumnFamily on that DB, until it is re-opened. This can lead to data loss on power loss. (For custom FileSystem implementations, this could lead to `FSDirectory::Fsync` or `FSDirectory::Close` after the first `FSDirectory::Close`; Also, valgrind could report call to `close()` with `fd=-1`.)
 * Fix a bug where `GenericRateLimiter` could revert the bandwidth set dynamically using `SetBytesPerSecond()` when a user configures a structure enclosing it, e.g., using `GetOptionsFromString()` to configure an `Options` that references an existing `RateLimiter` object.
 * Fix race conditions in `GenericRateLimiter`.
 * Fix a bug in `FIFOCompactionPicker::PickTTLCompaction` where total_size calculating might cause underflow
@@ -32,7 +33,7 @@
 * Provide support for ReadOptions.async_io with direct_io to improve Seek latency by using async IO to parallelize child iterator seek and doing asynchronous prefetching on sequential scans.
 * Added support for blob caching in order to cache frequently used blobs for BlobDB.
   * User can configure the new ColumnFamilyOptions `blob_cache` to enable/disable blob caching.
-  * Either sharing the backend cache with the block cache or using a completely separate cache is supported. 
+  * Either sharing the backend cache with the block cache or using a completely separate cache is supported.
   * A new abstraction interface called `BlobSource` for blob read logic gives all users access to blobs, whether they are in the blob cache, secondary cache, or (remote) storage. Blobs can be potentially read both while handling user reads (`Get`, `MultiGet`, or iterator) and during compaction (while dealing with compaction filters, Merges, or garbage collection) but eventually all blob reads go through `Version::GetBlob` or, for MultiGet, `Version::MultiGetBlob` (and then get dispatched to the interface -- `BlobSource`).
 * Add experimental tiered compaction feature `AdvancedColumnFamilyOptions::preclude_last_level_data_seconds`, which makes sure the new data inserted within preclude_last_level_data_seconds won't be placed on cold tier (the feature is not complete).
 

db/column_family.cc

@@ -699,19 +699,6 @@ ColumnFamilyData::~ColumnFamilyData() {
           id_, name_.c_str());
     }
   }
-
-  if (data_dirs_.size()) {  // Explicitly close data directories
-    Status s = Status::OK();
-    for (auto& data_dir_ptr : data_dirs_) {
-      if (data_dir_ptr) {
-        s = data_dir_ptr->Close(IOOptions(), nullptr);
-        if (!s.ok()) {
-          // TODO(zichen): add `Status Close()` and `CloseDirectories()
-          s.PermitUncheckedError();
-        }
-      }
-    }
-  }
 }
 
 bool ColumnFamilyData::UnrefAndTryDelete() {

db/db_basic_test.cc

@@ -1209,9 +1209,9 @@ TEST_F(DBBasicTest, DBCloseAllDirectoryFDs) {
   s = db->Close();
   auto* counted_fs =
       options.env->GetFileSystem()->CheckedCast<CountedFileSystem>();
-  assert(counted_fs);
-  ASSERT_TRUE(counted_fs->counters()->dir_opens ==
-              counted_fs->counters()->dir_closes);
+  ASSERT_TRUE(counted_fs != nullptr);
+  ASSERT_EQ(counted_fs->counters()->dir_opens,
+            counted_fs->counters()->dir_closes);
   ASSERT_OK(s);
   delete db;
 }

db/db_impl/db_impl.h

@@ -118,7 +118,6 @@ class Directories {
   IOStatus Close(const IOOptions& options, IODebugContext* dbg) {
     // close all directories for all database paths
     IOStatus s = IOStatus::OK();
-    IOStatus temp_s = IOStatus::OK();
 
     // The default implementation for Close() in Directory/FSDirectory class
     // "NotSupported" status, the upper level interface should be able to
@@ -127,53 +126,35 @@ class Directories {
     // `FSDirectory::Close()` yet
 
     if (db_dir_) {
-      temp_s = db_dir_->Close(options, dbg);
-      if (!temp_s.ok()) {
-        if (temp_s.IsNotSupported()) {
-          temp_s.PermitUncheckedError();
-        } else {
-          s = temp_s;
-        }
+      IOStatus temp_s = db_dir_->Close(options, dbg);
+      if (!temp_s.ok() && !temp_s.IsNotSupported() && s.ok()) {
+        s = std::move(temp_s);
       }
     }
 
-    if (!s.ok()) {
-      return s;
-    }
+    // Attempt to close everything even if one fails
+    s.PermitUncheckedError();
 
     if (wal_dir_) {
-      s = wal_dir_->Close(options, dbg);
-      if (!temp_s.ok()) {
-        if (temp_s.IsNotSupported()) {
-          temp_s.PermitUncheckedError();
-        } else {
-          s = temp_s;
-        }
+      IOStatus temp_s = wal_dir_->Close(options, dbg);
+      if (!temp_s.ok() && !temp_s.IsNotSupported() && s.ok()) {
+        s = std::move(temp_s);
       }
     }
 
-    if (!s.ok()) {
-      return s;
-    }
+    s.PermitUncheckedError();
 
-    if (data_dirs_.size() > 0 && s.ok()) {
-      for (auto& data_dir_ptr : data_dirs_) {
-        if (data_dir_ptr) {
-          temp_s = data_dir_ptr->Close(options, dbg);
-          if (!temp_s.ok()) {
-            if (temp_s.IsNotSupported()) {
-              temp_s.PermitUncheckedError();
-            } else {
-              return temp_s;
-            }
-          }
+    for (auto& data_dir_ptr : data_dirs_) {
+      if (data_dir_ptr) {
+        IOStatus temp_s = data_dir_ptr->Close(options, dbg);
+        if (!temp_s.ok() && !temp_s.IsNotSupported() && s.ok()) {
+          s = std::move(temp_s);
         }
       }
     }
 
-    // Mark temp_s as checked when temp_s is still the initial status
-    // (IOStatus::OK(), not checked yet)
-    temp_s.PermitUncheckedError();
+    // Ready for caller
+    s.MustCheck();
     return s;
   }
 

db/db_impl/db_impl_open.cc

@@ -541,6 +541,7 @@ Status DBImpl::Recover(
     s = CheckConsistency();
   }
   if (s.ok() && !read_only) {
+    // TODO: share file descriptors (FSDirectory) with SetDirectories above
     std::map<std::string, std::shared_ptr<FSDirectory>> created_dirs;
     for (auto cfd : *versions_->GetColumnFamilySet()) {
       s = cfd->AddDirectories(&created_dirs);

env/io_posix.cc

@@ -1678,6 +1678,7 @@ IOStatus PosixDirectory::Close(const IOOptions& /*opts*/,
 IOStatus PosixDirectory::FsyncWithDirOptions(
     const IOOptions& /*opts*/, IODebugContext* /*dbg*/,
     const DirFsyncOptions& dir_fsync_options) {
+  assert(fd_ >= 0);  // Check use after close
   IOStatus s = IOStatus::OK();
 #ifndef OS_AIX
   if (is_btrfs_) {

utilities/counted_fs.cc

@@ -211,6 +211,7 @@ class CountedRandomRWFile : public FSRandomRWFileOwnerWrapper {
 class CountedDirectory : public FSDirectoryWrapper {
  private:
   mutable CountedFileSystem* fs_;
+  bool closed_ = false;
 
  public:
   CountedDirectory(std::unique_ptr<FSDirectory>&& f, CountedFileSystem* fs)
@@ -229,6 +230,7 @@ class CountedDirectory : public FSDirectoryWrapper {
     if (rv.ok()) {
       fs_->counters()->closes++;
       fs_->counters()->dir_closes++;
+      closed_ = true;
     }
     return rv;
   }
@@ -242,6 +244,14 @@ class CountedDirectory : public FSDirectoryWrapper {
     }
     return rv;
   }
+
+  ~CountedDirectory() {
+    if (!closed_) {
+      // TODO: fix DB+CF code to use explicit Close, not rely on destructor
+      fs_->counters()->closes++;
+      fs_->counters()->dir_closes++;
+    }
+  }
 };
 }  // anonymous namespace