Revert "[libc] implement cached process/thread identity" (#99559)

Reverts #98989

Author: SchrodingerZhu

libc/config/config.json

@@ -75,16 +75,6 @@
     "LIBC_CONF_FREELIST_MALLOC_BUFFER_SIZE": {
       "value": 1073741824,
       "doc": "Default size for the constinit freelist buffer used for the freelist malloc implementation (default 1o 1GB)."
-    },
-  },
-  "unistd": {
-    "LIBC_CONF_ENABLE_TID_CACHE": {
-      "value": true,
-      "doc": "Enable caching mechanism for gettid to avoid syscall (only effective in fullbuild mode, default to true). Please refer to Undefined Behavior documentation for implications."
-    },
-    "LIBC_CONF_ENABLE_PID_CACHE": {
-      "value": true,
-      "doc": "Enable caching mechanism for getpid to avoid syscall (default to true). Please refer to Undefined Behavior documentation for implications."
     }
   },
   "math": {

libc/config/linux/aarch64/entrypoints.txt

@@ -297,7 +297,6 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.geteuid
     libc.src.unistd.getpid
     libc.src.unistd.getppid
-    libc.src.unistd.gettid
     libc.src.unistd.getuid
     libc.src.unistd.isatty
     libc.src.unistd.link

libc/config/linux/riscv/entrypoints.txt

@@ -296,7 +296,6 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.geteuid
     libc.src.unistd.getpid
     libc.src.unistd.getppid
-    libc.src.unistd.gettid
     libc.src.unistd.getuid
     libc.src.unistd.isatty
     libc.src.unistd.link

libc/config/linux/x86_64/entrypoints.txt

@@ -315,7 +315,6 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.unistd.geteuid
     libc.src.unistd.getpid
     libc.src.unistd.getppid
-    libc.src.unistd.gettid
     libc.src.unistd.getuid
     libc.src.unistd.isatty
     libc.src.unistd.link

libc/docs/configure.rst

@@ -52,6 +52,3 @@ to learn about the defaults for your platform and target.
 * **"string" options**
     - ``LIBC_CONF_MEMSET_X86_USE_SOFTWARE_PREFETCHING``: Inserts prefetch for write instructions (PREFETCHW) for memset on x86 to recover performance when hardware prefetcher is disabled.
     - ``LIBC_CONF_STRING_UNSAFE_WIDE_READ``: Read more than a byte at a time to perform byte-string operations like strlen.
-* **"unistd" options**
-    - ``LIBC_CONF_ENABLE_PID_CACHE``: Enable caching mechanism for getpid to avoid syscall (default to true). Please refer to Undefined Behavior documentation for implications.
-    - ``LIBC_CONF_ENABLE_TID_CACHE``: Enable caching mechanism for gettid to avoid syscall (only effective in fullbuild mode, default to true). Please refer to Undefined Behavior documentation for implications.

libc/docs/dev/undefined_behavior.rst

@@ -93,26 +93,3 @@ direction in this case.
 Non-const Constant Return Values
 --------------------------------
 Some libc functions, like ``dlerror()``, return ``char *`` instead of ``const char *`` and then tell the caller they promise not to to modify this value. Any modification of this value is undefined behavior.
-
-Cached ``getpid/gettid``
-------------------------
-Since version ``2.25``, glibc removes its cache mechanism for ``getpid/gettid`` 
-(See the history section in https://man7.org/linux/man-pages/man2/getpid.2.html).
-LLVM's libc still implements the cache as it is useful for fast deadlock detection.
-The cache mechanism is also implemented in MUSL and bionic. The tid/pid cache can 
-be disabled by setting ``LIBC_CONF_ENABLE_TID_CACHE`` and ``LIBC_CONF_ENABLE_PID_CACHE``
-to ``false`` respectively.
-
-Unwrapped ``SYS_clone/SYS_fork/SYS_vfork``
-------------------------------------------
-It is highly discouraged to use unwrapped ``SYS_clone/SYS_fork/SYS_vfork``. 
-First, calling such syscalls without provided libc wrappers ignores 
-all the ``pthread_atfork`` entries as libc can no longer detect the ``fork``. 
-Second, libc relies on the ``fork/clone`` wrappers to correctly maintain cache for
-process id and thread id, and other important process-specific states such as the list 
-of robust mutexes. Third, even if the user is to call ``exec*`` functions immediately, 
-there can still be other unexpected issues. For instance, there can be signal handlers 
-inherited from parent process triggered inside the instruction window between ``fork`` 
-and ``exec*``. As libc failed to maintain its internal states correctly, even though the
-functions used inside the signal handlers are marked as ``async-signal-safe`` (such as
-``getpid``), they will still return wrong values or lead to other even worse situations.

libc/spec/posix.td

@@ -546,11 +546,6 @@ def POSIX : StandardSpec<"POSIX"> {
           RetValSpec<PidT>,
           [ArgSpec<VoidType>]
         >,
-        FunctionSpec<
-          "gettid",
-          RetValSpec<PidT>,
-          [ArgSpec<VoidType>]
-        >,
         FunctionSpec<
           "getuid",
           RetValSpec<UidT>,
@@ -606,6 +601,16 @@ def POSIX : StandardSpec<"POSIX"> {
           RetValSpec<IntType>,
           [ArgSpec<ConstCharPtr>]
         >,
+        FunctionSpec<
+          "getpid",
+          RetValSpec<IntType>,
+          [ArgSpec<VoidType>]
+        >,
+        FunctionSpec<
+          "getppid",
+          RetValSpec<IntType>,
+          [ArgSpec<VoidType>]
+        >,
         FunctionSpec<
           "link",
           RetValSpec<IntType>,

libc/src/__support/OSUtil/CMakeLists.txt

@@ -15,20 +15,3 @@ add_object_library(
   DEPENDS
     ${target_os_util}
 )
-
-if (LIBC_CONF_ENABLE_PID_CACHE)
-  set(libc_copt_enable_pid_cache 1)
-else()
-  set(libc_copt_enable_pid_cache 0)
-endif()
-
-if(TARGET libc.src.__support.OSUtil.${LIBC_TARGET_OS}.pid)
-  add_object_library(
-    pid
-    ALIAS
-    DEPENDS
-      .${LIBC_TARGET_OS}.pid
-    COMPILE_OPTIONS
-      -DLIBC_COPT_ENABLE_PID_CACHE=${libc_copt_enable_pid_cache}
-  )
-endif()

libc/src/__support/OSUtil/linux/CMakeLists.txt

@@ -23,16 +23,3 @@ add_object_library(
     libc.hdr.types.struct_f_owner_ex
     libc.hdr.types.off_t
 )
-
-add_object_library(
-  pid
-  SRCS
-    pid.cpp
-  HDRS
-    ../pid.h
-  DEPENDS
-    libc.src.__support.OSUtil.osutil
-    libc.src.__support.common
-    libc.hdr.types.pid_t
-    libc.include.sys_syscall
-)

libc/src/__support/OSUtil/linux/pid.cpp

@@ -44,12 +44,6 @@ if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.mutex)
   )
 endif()
 
-if (LIBC_CONF_ENABLE_TID_CACHE)
-  set(libc_copt_enable_tid_cache 1)
-else()
-  set(libc_copt_enable_tid_cache 0)
-endif()
-
 add_header_library(
   thread_common
   HDRS
@@ -60,9 +54,6 @@ add_header_library(
     libc.src.__support.CPP.optional
     libc.src.__support.CPP.string_view
     libc.src.__support.CPP.stringstream
-    libc.hdr.types.pid_t
-  COMPILE_OPTIONS
-    -DLIBC_COPT_ENABLE_TID_CACHE=${libc_copt_enable_tid_cache}
 )
 
 if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.thread)
@@ -98,21 +89,3 @@ if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.CndVar)
     .${LIBC_TARGET_OS}.CndVar
   )
 endif()
-
-set(tid_dep)
-if (LLVM_LIBC_FULL_BUILD)
-  list(APPEND tid_dep libc.src.__support.thread)
-else()
-  list(APPEND tid_dep libc.src.__support.OSUtil.osutil)
-  list(APPEND tid_dep libc.include.sys_syscall)
-endif()
-
-add_header_library(
-  tid
-  HDRS
-    tid.h
-  DEPENDS
-    libc.src.__support.common
-    libc.hdr.types.pid_t
-    ${tid_dep}
-)

libc/src/__support/OSUtil/pid.h

@@ -55,7 +55,6 @@ add_header_library(
     libc.src.__support.common
     libc.src.__support.OSUtil.osutil
     libc.src.__support.CPP.limits
-    libc.src.__support.threads.tid
   COMPILE_OPTIONS
     -DLIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT=${LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT}
     ${monotonicity_flags}

libc/src/__support/threads/CMakeLists.txt

@@ -23,7 +23,6 @@
 #include "src/__support/threads/linux/futex_word.h"
 #include "src/__support/threads/linux/raw_mutex.h"
 #include "src/__support/threads/sleep.h"
-#include "src/__support/threads/tid.h"
 
 #ifndef LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT
 #define LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT 100
@@ -337,6 +336,8 @@ class RwLock {
   LIBC_INLINE Role get_preference() const {
     return static_cast<Role>(preference);
   }
+  // TODO: use cached thread id once implemented.
+  LIBC_INLINE static pid_t gettid() { return syscall_impl<pid_t>(SYS_gettid); }
 
   template <Role role> LIBC_INLINE LockResult try_lock(RwState &old) {
     if constexpr (role == Role::Reader) {
@@ -358,7 +359,7 @@ class RwLock {
         if (LIBC_LIKELY(old.compare_exchange_weak_with(
                 state, old.set_writer_bit(), cpp::MemoryOrder::ACQUIRE,
                 cpp::MemoryOrder::RELAXED))) {
-          writer_tid.store(gettid_inline(), cpp::MemoryOrder::RELAXED);
+          writer_tid.store(gettid(), cpp::MemoryOrder::RELAXED);
           return LockResult::Success;
         }
         // Notice that old is updated by the compare_exchange_weak_with
@@ -393,7 +394,7 @@ class RwLock {
             unsigned spin_count = LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT) {
     // Phase 1: deadlock detection.
     // A deadlock happens if this is a RAW/WAW lock in the same thread.
-    if (writer_tid.load(cpp::MemoryOrder::RELAXED) == gettid_inline())
+    if (writer_tid.load(cpp::MemoryOrder::RELAXED) == gettid())
       return LockResult::Deadlock;
 
 #if LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY
@@ -519,7 +520,7 @@ class RwLock {
     if (old.has_active_writer()) {
       // The lock is held by a writer.
       // Check if we are the owner of the lock.
-      if (writer_tid.load(cpp::MemoryOrder::RELAXED) != gettid_inline())
+      if (writer_tid.load(cpp::MemoryOrder::RELAXED) != gettid())
         return LockResult::PermissionDenied;
       // clear writer tid.
       writer_tid.store(0, cpp::MemoryOrder::RELAXED);

libc/src/__support/threads/linux/CMakeLists.txt

@@ -518,6 +518,4 @@ void thread_exit(ThreadReturnValue retval, ThreadStyle style) {
   __builtin_unreachable();
 }
 
-pid_t Thread::get_uncached_tid() { return syscall_impl<pid_t>(SYS_gettid); }
-
 } // namespace LIBC_NAMESPACE_DECL

libc/src/__support/threads/linux/rwlock.h

@@ -9,11 +9,6 @@
 #ifndef LLVM_LIBC_SRC___SUPPORT_THREADS_THREAD_H
 #define LLVM_LIBC_SRC___SUPPORT_THREADS_THREAD_H
 
-#ifndef LIBC_COPT_ENABLE_TID_CACHE
-#define LIBC_COPT_ENABLE_TID_CACHE 1
-#endif
-
-#include "hdr/types/pid_t.h"
 #include "src/__support/CPP/atomic.h"
 #include "src/__support/CPP/optional.h"
 #include "src/__support/CPP/string_view.h"
@@ -108,7 +103,7 @@ struct alignas(STACK_ALIGNMENT) ThreadAttributes {
   uintptr_t tls;                // Address to the thread TLS memory
   uintptr_t tls_size;           // The size of area pointed to by |tls|.
   unsigned char owned_stack; // Indicates if the thread owns this stack memory
-  pid_t tid;
+  int tid;
   ThreadStyle style;
   ThreadReturnValue retval;
   ThreadAtExitCallbackMgr *atexit_callback_mgr;
@@ -233,26 +228,6 @@ struct Thread {
 
   // Return the name of the thread in |name|. Return the error number of error.
   int get_name(cpp::StringStream &name) const;
-
-  static pid_t get_uncached_tid();
-
-  LIBC_INLINE void refresh_tid(pid_t cached = -1) {
-    if (cached >= 0)
-      this->attrib->tid = cached;
-    else
-      this->attrib->tid = get_uncached_tid();
-  }
-  LIBC_INLINE void invalidate_tid() { this->attrib->tid = -1; }
-
-  LIBC_INLINE pid_t get_tid() {
-#if LIBC_COPT_ENABLE_TID_CACHE
-    if (LIBC_UNLIKELY(this->attrib->tid < 0))
-      return get_uncached_tid();
-    return this->attrib->tid;
-#else
-    return get_uncached_tid();
-#endif
-  }
 };
 
 extern LIBC_THREAD_LOCAL Thread self;