Rollup merge of #126827 - the8472:pidfd-spawn, r=workingjubilee

Use pidfd_spawn for faster process spawning when a PidFd is requested glibc 2.39 added `pidfd_spawnp` and `pidfd_getpid` which makes it possible to get pidfds while staying on the CLONE_VFORK path. verified that vfork gets used with strace: ``` $ strace -ff -e pidfd_open,clone3,openat,execve,waitid,close ./x test std --no-doc -- pidfd [...] [pid 2820532] clone3({flags=CLONE_VM|CLONE_PIDFD|CLONE_VFORK|CLONE_CLEAR_SIGHAND, pidfd=0x7b7f885fec6c, exit_signal=SIGCHLD, stack=0x7b7f88aff000, stack_size=0x9500}strace: Process 2820533 attached <unfinished ...> [pid 2820533] execve("/home/the8472/bin/sleep", ["sleep", "1000"], 0x7ffdd0e268d8 /* 107 vars */) = -1 ENOENT (No such file or directory) [pid 2820533] execve("/home/the8472/.cargo/bin/sleep", ["sleep", "1000"], 0x7ffdd0e268d8 /* 107 vars */) = -1 ENOENT (No such file or directory) [pid 2820533] execve("/usr/local/bin/sleep", ["sleep", "1000"], 0x7ffdd0e268d8 /* 107 vars */) = -1 ENOENT (No such file or directory) [pid 2820533] execve("/usr/bin/sleep", ["sleep", "1000"], 0x7ffdd0e268d8 /* 107 vars */ <unfinished ...> [pid 2820532] <... clone3 resumed> => {pidfd=[3]}, 88) = 2820533 [pid 2820533] <... execve resumed>) = 0 [pid 2820532] openat(AT_FDCWD, "/proc/self/fdinfo/3", O_RDONLY|O_CLOEXEC) = 4 [pid 2820532] close(4) = 0 ``` Tracking issue: #82971
rust-lang · Jul 12, 2024 · f9b3e8b · f9b3e8b
2 parents 18152d7 ec0c755
commit f9b3e8b
Show file tree

Hide file tree

Showing 3 changed files with 131 additions and 6 deletions.
diff --git a/library/std/src/sys/pal/unix/linux/pidfd/tests.rs b/library/std/src/sys/pal/unix/linux/pidfd/tests.rs
@@ -1,7 1,7 @@
 use crate::assert_matches::assert_matches;
 use crate::os::fd::{AsRawFd, RawFd};
-use crate::os::linux::process::{ChildExt, CommandExt};
-use crate::os::unix::process::ExitStatusExt;
 use crate::os::linux::process::{ChildExt, CommandExt as _};
 use crate::os::unix::process::{CommandExt as _, ExitStatusExt};
 use crate::process::Command;
 
 #[test]
@@ -21,6 21,7 @@ fn test_command_pidfd() {
  let flags = super::cvt(unsafe { libc::fcntl(pidfd.as_raw_fd(), libc::F_GETFD) }).unwrap();
  assert!(flags & libc::FD_CLOEXEC != 0);
  }
  assert!(child.id() > 0 && child.id() < -1i32 as u32);
  let status = child.wait().expect("error waiting on pidfd");
  assert_eq!(status.code(), Some(1));
 
@@ -42,6 43,17 @@ fn test_command_pidfd() {
  .unwrap()
  .pidfd()
  .expect_err("pidfd should not have been created");
 
  // exercise the fork/exec path since the earlier attempts may have used pidfd_spawnp()
  let mut child =
  unsafe { Command::new("false").pre_exec(|| Ok(())) }.create_pidfd(true).spawn().unwrap();
 
  assert!(child.id() > 0 && child.id() < -1i32 as u32);
 
  if pidfd_open_available {
  assert!(child.pidfd().is_ok())
  }
  child.wait().expect("error waiting on child");
 }
 
 #[test]

diff --git a/library/std/src/sys/pal/unix/mod.rs b/library/std/src/sys/pal/unix/mod.rs
@@ -305,10 305,13 @@ macro_rules! impl_is_minus_one {
 
 impl_is_minus_one! { i8 i16 i32 i64 isize }
 
 /// Convert native return values to Result using the *-1 means error is in `errno`* convention.
 /// Non-error values are `Ok`-wrapped.
 pub fn cvt<T: IsMinusOne>(t: T) -> crate::io::Result<T> {
  if t.is_minus_one() { Err(crate::io::Error::last_os_error()) } else { Ok(t) }
 }
 
 /// `-1` → look at `errno` → retry on `EINTR`. Otherwise `Ok()`-wrap the closure return value.
 pub fn cvt_r<T, F>(mut f: F) -> crate::io::Result<T>
 where
  T: IsMinusOne,
@@ -323,6 326,7 @@ where
 }
 
 #[allow(dead_code)] // Not used on all platforms.
 /// Zero means `Ok()`, all other values are treated as raw OS errors. Does not look at `errno`.
 pub fn cvt_nz(error: libc::c_int) -> crate::io::Result<()> {
  if error == 0 { Ok(()) } else { Err(crate::io::Error::from_raw_os_error(error)) }
 }

diff --git a/library/std/src/sys/pal/unix/process/process_unix.rs b/library/std/src/sys/pal/unix/process/process_unix.rs
@@ -449,17 449,82 @@ impl Command {
  use crate::mem::MaybeUninit;
  use crate::sys::weak::weak;
  use crate::sys::{self, cvt_nz, on_broken_pipe_flag_used};
  #[cfg(target_os = "linux")]
  use core::sync::atomic::{AtomicU8, Ordering};
 
  if self.get_gid().is_some()
  || self.get_uid().is_some()
  || (self.env_saw_path() && !self.program_is_path())
  || !self.get_closures().is_empty()
  || self.get_groups().is_some()
- || self.get_create_pidfd()
  {
  return Ok(None);
  }
 
  cfg_if::cfg_if! {
  if #[cfg(target_os = "linux")] {
  weak! {
  fn pidfd_spawnp(
  *mut libc::c_int,
  *const libc::c_char,
  *const libc::posix_spawn_file_actions_t,
  *const libc::posix_spawnattr_t,
  *const *mut libc::c_char,
  *const *mut libc::c_char
  ) -> libc::c_int
  }
 
  weak! { fn pidfd_getpid(libc::c_int) -> libc::c_int }
 
  static PIDFD_SUPPORTED: AtomicU8 = AtomicU8::new(0);
  const UNKNOWN: u8 = 0;
  const SPAWN: u8 = 1;
  // Obtaining a pidfd via the fork exec path might work
  const FORK_EXEC: u8 = 2;
  // Neither pidfd_spawn nor fork/exec will get us a pidfd.
  // Instead we'll just posix_spawn if the other preconditions are met.
  const NO: u8 = 3;
 
  if self.get_create_pidfd() {
  let mut support = PIDFD_SUPPORTED.load(Ordering::Relaxed);
  if support == FORK_EXEC {
  return Ok(None);
  }
  if support == UNKNOWN {
  support = NO;
  let our_pid = crate::process::id();
  let pidfd = cvt(unsafe { libc::syscall(libc::SYS_pidfd_open, our_pid, 0) } as c_int);
  match pidfd {
  Ok(pidfd) => {
  support = FORK_EXEC;
  if let Some(Ok(pid)) = pidfd_getpid.get().map(|f| cvt(unsafe { f(pidfd) } as i32)) {
  if pidfd_spawnp.get().is_some() && pid as u32 == our_pid {
  support = SPAWN
  }
  }
  unsafe { libc::close(pidfd) };
  }
  Err(e) if e.raw_os_error() == Some(libc::EMFILE) => {
  // We're temporarily(?) out of file descriptors. In this case obtaining a pidfd would also fail
  // Don't update the support flag so we can probe again later.
  return Err(e)
  }
  _ => {}
  }
  PIDFD_SUPPORTED.store(support, Ordering::Relaxed);
  if support == FORK_EXEC {
  return Ok(None);
  }
  }
  core::assert_matches::debug_assert_matches!(support, SPAWN | NO);
  }
  } else {
  if self.get_create_pidfd() {
  unreachable!("only implemented on linux")
  }
  }
  }
 
  // Only glibc 2.24 posix_spawn() supports returning ENOENT directly.
  #[cfg(all(target_os = "linux", target_env = "gnu"))]
  {
@@ -543,9 608,6 @@ impl Command {
 
  let pgroup = self.get_pgroup();
 
- // Safety: -1 indicates we don't have a pidfd.
- let mut p = unsafe { Process::new(0, -1) };
-
  struct PosixSpawnFileActions<'a>(&'a mut MaybeUninit<libc::posix_spawn_file_actions_t>);
 
  impl Drop for PosixSpawnFileActions<'_> {
@@ -640,6 702,47 @@ impl Command {
  #[cfg(target_os = "nto")]
  let spawn_fn = retrying_libc_posix_spawnp;
 
  #[cfg(target_os = "linux")]
  if self.get_create_pidfd() && PIDFD_SUPPORTED.load(Ordering::Relaxed) == SPAWN {
  let mut pidfd: libc::c_int = -1;
  let spawn_res = pidfd_spawnp.get().unwrap()(
  &mut pidfd,
  self.get_program_cstr().as_ptr(),
  file_actions.0.as_ptr(),
  attrs.0.as_ptr(),
  self.get_argv().as_ptr() as *const _,
  envp as *const _,
  );
 
  let spawn_res = cvt_nz(spawn_res);
  if let Err(ref e) = spawn_res
  && e.raw_os_error() == Some(libc::ENOSYS)
  {
  PIDFD_SUPPORTED.store(FORK_EXEC, Ordering::Relaxed);
  return Ok(None);
  }
  spawn_res?;
 
  let pid = match cvt(pidfd_getpid.get().unwrap()(pidfd)) {
  Ok(pid) => pid,
  Err(e) => {
  // The child has been spawned and we are holding its pidfd.
  // But we cannot obtain its pid even though pidfd_getpid support was verified earlier.
  // This might happen if libc can't open procfs because the file descriptor limit has been reached.
  libc::close(pidfd);
  return Err(Error::new(
  e.kind(),
  "pidfd_spawnp succeeded but the child's PID could not be obtained",
  ));
  }
  };
 
  return Ok(Some(Process::new(pid, pidfd)));
  }
 
  // Safety: -1 indicates we don't have a pidfd.
  let mut p = Process::new(0, -1);
 
  let spawn_res = spawn_fn(
  &mut p.pid,
  self.get_program_cstr().as_ptr(),
@@ -786,6 889,12 @@ pub struct Process {
 
 impl Process {
  #[cfg(target_os = "linux")]
  /// # Safety
  ///
  /// `pidfd` must either be -1 (representing no file descriptor) or a valid, exclusively owned file
  /// descriptor (See [I/O Safety]).
  ///
  /// [I/O Safety]: crate::io#io-safety
  unsafe fn new(pid: pid_t, pidfd: pid_t) -> Self {
  use crate::os::unix::io::FromRawFd;
  use crate::sys_common::FromInner;