From d7de392b05e015f669012db65395f26daaa53f14 Mon Sep 17 00:00:00 2001 From: "ivan.penkov@gmail.com" Date: Wed, 15 Aug 2012 22:09:42 +0000 Subject: Fixing a race condition in the Crash Generation Server which has to do with simultaneous handling of dump requests and client process termination events. http://breakpad.appspot.com/430002/ git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1013 4c0a9323-5329-0410-9bdc-e9ce6186880e --- src/client/windows/crash_generation/client_info.cc | 40 ++-- src/client/windows/crash_generation/client_info.h | 18 +- .../crash_generation/crash_generation_server.cc | 254 ++++++++++++--------- .../crash_generation/crash_generation_server.h | 14 +- 4 files changed, 179 insertions(+), 147 deletions(-) diff --git a/src/client/windows/crash_generation/client_info.cc b/src/client/windows/crash_generation/client_info.cc index 60bbac82..ca10caa4 100644 --- a/src/client/windows/crash_generation/client_info.cc +++ b/src/client/windows/crash_generation/client_info.cc @@ -85,16 +85,38 @@ bool ClientInfo::Initialize() { return dump_generated_handle_ != NULL; } -ClientInfo::~ClientInfo() { +void ClientInfo::UnregisterDumpRequestWaitAndBlockUntilNoPending() { if (dump_request_wait_handle_) { // Wait for callbacks that might already be running to finish. UnregisterWaitEx(dump_request_wait_handle_, INVALID_HANDLE_VALUE); + dump_request_wait_handle_ = NULL; } +} +void ClientInfo::UnregisterProcessExitWait(bool block_until_no_pending) { if (process_exit_wait_handle_) { - // Wait for the callback that might already be running to finish. - UnregisterWaitEx(process_exit_wait_handle_, INVALID_HANDLE_VALUE); + if (block_until_no_pending) { + // Wait for the callback that might already be running to finish. + UnregisterWaitEx(process_exit_wait_handle_, INVALID_HANDLE_VALUE); + } else { + UnregisterWait(process_exit_wait_handle_); + } + process_exit_wait_handle_ = NULL; } +} + +ClientInfo::~ClientInfo() { + // Waiting for the callback to finish here is safe because ClientInfo's are + // never destroyed from the dump request handling callback. + UnregisterDumpRequestWaitAndBlockUntilNoPending(); + + // This is a little tricky because ClientInfo's may be destroyed by the same + // callback (OnClientEnd) and waiting for it to finish will cause a deadlock. + // Regardless of this complication, wait for any running callbacks to finish + // so that the common case is properly handled. In order to avoid deadlocks, + // the OnClientEnd callback must call UnregisterProcessExitWait(false) + // before deleting the ClientInfo. + UnregisterProcessExitWait(true); if (process_handle_) { CloseHandle(process_handle_); @@ -109,18 +131,6 @@ ClientInfo::~ClientInfo() { } } -void ClientInfo::UnregisterWaits() { - if (dump_request_wait_handle_) { - UnregisterWait(dump_request_wait_handle_); - dump_request_wait_handle_ = NULL; - } - - if (process_exit_wait_handle_) { - UnregisterWait(process_exit_wait_handle_); - process_exit_wait_handle_ = NULL; - } -} - bool ClientInfo::GetClientExceptionInfo(EXCEPTION_POINTERS** ex_info) const { SIZE_T bytes_count = 0; if (!ReadProcessMemory(process_handle_, diff --git a/src/client/windows/crash_generation/client_info.h b/src/client/windows/crash_generation/client_info.h index 999e6678..a24a82e7 100644 --- a/src/client/windows/crash_generation/client_info.h +++ b/src/client/windows/crash_generation/client_info.h @@ -67,24 +67,22 @@ class ClientInfo { HANDLE dump_generated_handle() const { return dump_generated_handle_; } DWORD crash_id() const { return crash_id_; } - HANDLE dump_request_wait_handle() const { - return dump_request_wait_handle_; - } - void set_dump_request_wait_handle(HANDLE value) { dump_request_wait_handle_ = value; } - HANDLE process_exit_wait_handle() const { - return process_exit_wait_handle_; - } - void set_process_exit_wait_handle(HANDLE value) { process_exit_wait_handle_ = value; } - // Unregister all waits for the client. - void UnregisterWaits(); + // Unregister the dump request wait operation and wait for all callbacks + // that might already be running to complete before returning. + void UnregisterDumpRequestWaitAndBlockUntilNoPending(); + + // Unregister the process exit wait operation. If block_until_no_pending is + // true, wait for all callbacks that might already be running to complete + // before returning. + void UnregisterProcessExitWait(bool block_until_no_pending); bool Initialize(); bool GetClientExceptionInfo(EXCEPTION_POINTERS** ex_info) const; diff --git a/src/client/windows/crash_generation/crash_generation_server.cc b/src/client/windows/crash_generation/crash_generation_server.cc index 477973c1..e67025eb 100644 --- a/src/client/windows/crash_generation/crash_generation_server.cc +++ b/src/client/windows/crash_generation/crash_generation_server.cc @@ -76,13 +76,6 @@ static const ULONG kPipeIOThreadFlags = WT_EXECUTEINWAITTHREAD; static const ULONG kDumpRequestThreadFlags = WT_EXECUTEINWAITTHREAD | WT_EXECUTELONGFUNCTION; -// Maximum delay during server shutdown if some work items -// are still executing. -static const int kShutdownDelayMs = 10000; - -// Interval for each sleep during server shutdown. -static const int kShutdownSleepIntervalMs = 5; - static bool IsClientRequestValid(const ProtocolMessage& msg) { return msg.tag == MESSAGE_TAG_UPLOAD_REQUEST || (msg.tag == MESSAGE_TAG_REGISTRATION_REQUEST && @@ -123,8 +116,7 @@ CrashGenerationServer::CrashGenerationServer( server_state_(IPC_SERVER_STATE_UNINITIALIZED), shutting_down_(false), overlapped_(), - client_info_(NULL), - cleanup_item_count_(0) { + client_info_(NULL) { InitializeCriticalSection(&sync_); if (dump_path) { @@ -132,91 +124,85 @@ CrashGenerationServer::CrashGenerationServer( } } +// This should never be called from the OnPipeConnected callback. +// Otherwise the UnregisterWaitEx call below will cause a deadlock. CrashGenerationServer::~CrashGenerationServer() { // New scope to release the lock automatically. { + // Make sure no clients are added or removed beyond this point. + // Before adding or removing any clients, the critical section + // must be entered and the shutting_down_ flag checked. The + // critical section is then exited only after the clients_ list + // modifications are done and the list is in a consistent state. AutoCriticalSection lock(&sync_); // Indicate to existing threads that server is shutting down. shutting_down_ = true; - - // Even if there are no current worker threads running, it is possible that - // an I/O request is pending on the pipe right now but not yet done. - // In fact, it's very likely this is the case unless we are in an ERROR - // state. If we don't wait for the pending I/O to be done, then when the I/O - // completes, it may write to invalid memory. AppVerifier will flag this - // problem too. So we disconnect from the pipe and then wait for the server - // to get into error state so that the pending I/O will fail and get - // cleared. - DisconnectNamedPipe(pipe_); - int num_tries = 100; - while (num_tries-- && server_state_ != IPC_SERVER_STATE_ERROR) { - lock.Release(); - Sleep(10); - lock.Acquire(); - } - - // Unregister wait on the pipe. - if (pipe_wait_handle_) { - // Wait for already executing callbacks to finish. - UnregisterWaitEx(pipe_wait_handle_, INVALID_HANDLE_VALUE); - } - - // Close the pipe to avoid further client connections. - if (pipe_) { - CloseHandle(pipe_); - } - - // Request all ClientInfo objects to unregister all waits. - std::list::iterator iter; - for (iter = clients_.begin(); iter != clients_.end(); ++iter) { - ClientInfo* client_info = *iter; - client_info->UnregisterWaits(); - } } + // No one will modify the clients_ list beyond this point - + // not even from another thread. - // Now that all waits have been unregistered, wait for some time - // for all pending work items to finish. - int total_wait = 0; - while (cleanup_item_count_ > 0) { - Sleep(kShutdownSleepIntervalMs); - - total_wait += kShutdownSleepIntervalMs; + // Even if there are no current worker threads running, it is possible that + // an I/O request is pending on the pipe right now but not yet done. + // In fact, it's very likely this is the case unless we are in an ERROR + // state. If we don't wait for the pending I/O to be done, then when the I/O + // completes, it may write to invalid memory. AppVerifier will flag this + // problem too. So we disconnect from the pipe and then wait for the server + // to get into error state so that the pending I/O will fail and get + // cleared. + DisconnectNamedPipe(pipe_); + int num_tries = 100; + while (num_tries-- && server_state_ != IPC_SERVER_STATE_ERROR) { + Sleep(10); + } - if (total_wait >= kShutdownDelayMs) { - break; - } + // Unregister wait on the pipe. + if (pipe_wait_handle_) { + // Wait for already executing callbacks to finish. + UnregisterWaitEx(pipe_wait_handle_, INVALID_HANDLE_VALUE); } - // New scope to hold the lock for the shortest time. - { - AutoCriticalSection lock(&sync_); + // Close the pipe to avoid further client connections. + if (pipe_) { + CloseHandle(pipe_); + } - // Clean up all the ClientInfo objects. - std::list::iterator iter; - for (iter = clients_.begin(); iter != clients_.end(); ++iter) { - ClientInfo* client_info = *iter; - delete client_info; - } + // Request all ClientInfo objects to unregister all waits. + // No need to enter the critical section because no one is allowed to modify + // the clients_ list once the shutting_down_ flag is set. + std::list::iterator iter; + for (iter = clients_.begin(); iter != clients_.end(); ++iter) { + ClientInfo* client_info = *iter; + // Unregister waits. Wait for already executing callbacks to finish. + // Unregister the client process exit wait first and only then unregister + // the dump request wait. The reason is that the OnClientExit callback + // also unregisters the dump request wait and such a race (doing the same + // unregistration from two threads) is undesirable. + client_info->UnregisterProcessExitWait(true); + client_info->UnregisterDumpRequestWaitAndBlockUntilNoPending(); - if (server_alive_handle_) { - // Release the mutex before closing the handle so that clients requesting - // dumps wait for a long time for the server to generate a dump. - ReleaseMutex(server_alive_handle_); - CloseHandle(server_alive_handle_); - } + // Destroying the ClientInfo here is safe because all wait operations for + // this ClientInfo were unregistered and no pending or running callbacks + // for this ClientInfo can possible exist (block_until_no_pending option + // was used). + delete client_info; + } - if (overlapped_.hEvent) { - CloseHandle(overlapped_.hEvent); - } + if (server_alive_handle_) { + // Release the mutex before closing the handle so that clients requesting + // dumps wait for a long time for the server to generate a dump. + ReleaseMutex(server_alive_handle_); + CloseHandle(server_alive_handle_); } + if (overlapped_.hEvent) { + CloseHandle(overlapped_.hEvent); + } + DeleteCriticalSection(&sync_); } bool CrashGenerationServer::Start() { - AutoCriticalSection lock(&sync_); - if (server_state_ != IPC_SERVER_STATE_UNINITIALIZED) { return false; } @@ -455,6 +441,7 @@ void CrashGenerationServer::HandleReadDoneState() { return; } + // This is only valid as long as it can be found in the clients_ list client_info_ = client_info.release(); // Note that the asynchronous write issued by RespondToClient function @@ -532,7 +519,32 @@ void CrashGenerationServer::HandleReadingAckState() { // The connection handshake with the client is now complete; perform // the callback. if (connect_callback_) { - connect_callback_(connect_context_, client_info_); + // Note that there is only a single copy of the ClientInfo of the + // currently connected client. However it is being referenced from + // two different places: + // - the client_info_ member + // - the clients_ list + // The lifetime of this ClientInfo depends on the lifetime of the + // client process - basically it can go away at any time. + // However, as long as it is referenced by the clients_ list it + // is guaranteed to be valid. Enter the critical section and check + // to see whether the client_info_ can be found in the list. + // If found, execute the callback and only then leave the critical + // section. + AutoCriticalSection lock(&sync_); + + bool client_is_still_alive = false; + std::list::iterator iter; + for (iter = clients_.begin(); iter != clients_.end(); ++iter) { + if (client_info_ == *iter) { + client_is_still_alive = true; + break; + } + } + + if (client_is_still_alive) { + connect_callback_(connect_context_, client_info_); + } } } else { // We should never get an I/O incomplete since we should not execute this @@ -605,16 +617,39 @@ bool CrashGenerationServer::PrepareReply(const ClientInfo& client_info, return true; } + // Closing of remote handles (belonging to a different process) can + // only be done through DuplicateHandle. if (reply->dump_request_handle) { - CloseHandle(reply->dump_request_handle); + DuplicateHandle(client_info.process_handle(), // hSourceProcessHandle + reply->dump_request_handle, // hSourceHandle + NULL, // hTargetProcessHandle + 0, // lpTargetHandle + 0, // dwDesiredAccess + FALSE, // bInheritHandle + DUPLICATE_CLOSE_SOURCE); // dwOptions + reply->dump_request_handle = NULL; } if (reply->dump_generated_handle) { - CloseHandle(reply->dump_generated_handle); + DuplicateHandle(client_info.process_handle(), // hSourceProcessHandle + reply->dump_generated_handle, // hSourceHandle + NULL, // hTargetProcessHandle + 0, // lpTargetHandle + 0, // dwDesiredAccess + FALSE, // bInheritHandle + DUPLICATE_CLOSE_SOURCE); // dwOptions + reply->dump_generated_handle = NULL; } if (reply->server_alive_handle) { - CloseHandle(reply->server_alive_handle); + DuplicateHandle(client_info.process_handle(), // hSourceProcessHandle + reply->server_alive_handle, // hSourceHandle + NULL, // hTargetProcessHandle + 0, // lpTargetHandle + 0, // dwDesiredAccess + FALSE, // bInheritHandle + DUPLICATE_CLOSE_SOURCE); // dwOptions + reply->server_alive_handle = NULL; } return false; @@ -676,21 +711,15 @@ bool CrashGenerationServer::RespondToClient(ClientInfo* client_info) { // Takes over ownership of client_info. We MUST return true if AddClient // succeeds. - if (!AddClient(client_info)) { - return false; - } - - return true; + return AddClient(client_info); } // The server thread servicing the clients runs this method. The method // implements the state machine described in ReadMe.txt along with the // helper methods HandleXXXState. void CrashGenerationServer::HandleConnectionRequest() { - AutoCriticalSection lock(&sync_); - - // If we are shutting doen then get into ERROR state, reset the event so more - // workers don't run and return immediately. + // If the server is shutting down, get into ERROR state, reset the event so + // more workers don't run and return immediately. if (shutting_down_) { server_state_ = IPC_SERVER_STATE_ERROR; ResetEvent(overlapped_.hEvent); @@ -776,6 +805,10 @@ bool CrashGenerationServer::AddClient(ClientInfo* client_info) { // New scope to hold the lock for the shortest time. { AutoCriticalSection lock(&sync_); + if (shutting_down_) { + // If server is shutting down, don't add new clients + return false; + } clients_.push_back(client_info); } @@ -812,56 +845,55 @@ void CALLBACK CrashGenerationServer::OnClientEnd(void* context, BOOLEAN) { CrashGenerationServer* crash_server = client_info->crash_server(); assert(crash_server); - client_info->UnregisterWaits(); - InterlockedIncrement(&crash_server->cleanup_item_count_); - - if (!QueueUserWorkItem(CleanupClient, context, WT_EXECUTEDEFAULT)) { - InterlockedDecrement(&crash_server->cleanup_item_count_); - } + crash_server->HandleClientProcessExit(client_info); } -// static -DWORD WINAPI CrashGenerationServer::CleanupClient(void* context) { - assert(context); - ClientInfo* client_info = reinterpret_cast(context); +void CrashGenerationServer::HandleClientProcessExit(ClientInfo* client_info) { + assert(client_info); - CrashGenerationServer* crash_server = client_info->crash_server(); - assert(crash_server); + // Must unregister the dump request wait operation and wait for any + // dump requests that might be pending to finish before proceeding + // with the client_info cleanup. + client_info->UnregisterDumpRequestWaitAndBlockUntilNoPending(); - if (crash_server->exit_callback_) { - crash_server->exit_callback_(crash_server->exit_context_, client_info); + if (exit_callback_) { + exit_callback_(exit_context_, client_info); } - crash_server->DoCleanup(client_info); - - InterlockedDecrement(&crash_server->cleanup_item_count_); - return 0; -} - -void CrashGenerationServer::DoCleanup(ClientInfo* client_info) { - assert(client_info); - // Start a new scope to release lock automatically. { AutoCriticalSection lock(&sync_); + if (shutting_down_) { + // The crash generation server is shutting down and as part of the + // shutdown process it will delete all clients from the clients_ list. + return; + } clients_.remove(client_info); } + // Explicitly unregister the process exit wait using the non-blocking method. + // Otherwise, the destructor will attempt to unregister it using the blocking + // method which will lead to a deadlock because it is being called from the + // callback of the same wait operation + client_info->UnregisterProcessExitWait(false); + delete client_info; } void CrashGenerationServer::HandleDumpRequest(const ClientInfo& client_info) { + bool execute_callback = true; // Generate the dump only if it's explicitly requested by the // server application; otherwise the server might want to generate // dump in the callback. std::wstring dump_path; if (generate_dumps_) { if (!GenerateDump(client_info, &dump_path)) { - return; + // client proccess terminated or some other error + execute_callback = false; } } - if (dump_callback_) { + if (dump_callback_ && execute_callback) { std::wstring* ptr_dump_path = (dump_path == L"") ? NULL : &dump_path; dump_callback_(dump_context_, &client_info, ptr_dump_path); } diff --git a/src/client/windows/crash_generation/crash_generation_server.h b/src/client/windows/crash_generation/crash_generation_server.h index ea3776fb..37278484 100644 --- a/src/client/windows/crash_generation/crash_generation_server.h +++ b/src/client/windows/crash_generation/crash_generation_server.h @@ -189,11 +189,8 @@ class CrashGenerationServer { // Callback for client process exit event. static void CALLBACK OnClientEnd(void* context, BOOLEAN timer_or_wait); - // Releases resources for a client. - static DWORD WINAPI CleanupClient(void* context); - - // Cleans up for the given client. - void DoCleanup(ClientInfo* client_info); + // Handles client process exit. + void HandleClientProcessExit(ClientInfo* client_info); // Adds the given client to the list of registered clients. bool AddClient(ClientInfo* client_info); @@ -216,8 +213,7 @@ class CrashGenerationServer { // asynchronous IO operation. void EnterStateWhenSignaled(IPCServerState state); - // Sync object for thread-safe access to the shared list of clients and - // the server's state. + // Sync object for thread-safe access to the shared list of clients. CRITICAL_SECTION sync_; // List of clients. @@ -286,10 +282,6 @@ class CrashGenerationServer { // Client Info for the client that's connecting to the server. ClientInfo* client_info_; - // Count of clean-up work items that are currently running or are - // already queued to run. - volatile LONG cleanup_item_count_; - // Disable copy ctor and operator=. CrashGenerationServer(const CrashGenerationServer& crash_server); CrashGenerationServer& operator=(const CrashGenerationServer& crash_server); -- cgit v1.2.1