bjoernager/rust
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explain mem::forget(env_lock) in fork/exec

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Ralf Jung 2022-12-12 09:49:42 +01:00
parent 2cd2070af7
commit 3465d5fb16
1 changed files with 4 additions and 3 deletions
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7
library/std/src/sys/unix/process/process_unix.rs
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@ -66,14 +66,15 @@ impl Command {
// //
// Note that as soon as we're done with the fork there's no need to hold // Note that as soon as we're done with the fork there's no need to hold
// a lock any more because the parent won't do anything and the child is // a lock any more because the parent won't do anything and the child is
// in its own process. Thus the parent drops the lock guard while the child // in its own process. Thus the parent drops the lock guard immediately.
// forgets it to avoid unlocking it on a new thread, which would be invalid. // The child calls `mem::forget` to leak the lock, which is crucial because
// releasing a lock is not async-signal-safe.
let env_lock = sys::os::env_read_lock(); let env_lock = sys::os::env_read_lock();
let (pid, pidfd) = unsafe { self.do_fork()? }; let (pid, pidfd) = unsafe { self.do_fork()? };
if pid == 0 { if pid == 0 {
crate::panic::always_abort(); crate::panic::always_abort();
mem::forget(env_lock); mem::forget(env_lock); // avoid non-async-signal-safe unlocking
drop(input); drop(input);
let Err(err) = unsafe { self.do_exec(theirs, envp.as_ref()) }; let Err(err) = unsafe { self.do_exec(theirs, envp.as_ref()) };
let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32; let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;