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Rollup merge of #88828 - FabianWolff:issue-88585, r=dtolnay

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Use `libc::sigaction()` instead of `sys::signal()` to prevent a deadlock

Fixes #88585. POSIX [specifies](https://man7.org/linux/man-pages/man3/fork.3p.html) that after forking,
> to avoid errors, the child process may only execute async-signal-safe operations until such time as one of the exec functions is called.

Rust's standard library does not currently adhere to this, as evidenced by #88585. The child process calls [`sys::signal()`](7bf0736e13/library/std/src/sys/unix/android.rs (L76)), which on Android calls [`libc::dlsym()`](7bf0736e13/library/std/src/sys/unix/weak.rs (L101)), which is [**not**](https://man7.org/linux/man-pages/man7/signal-safety.7.html) async-signal-safe, and in fact causes a deadlock in the example in #88585.

I think the easiest solution here would be to just call `libc::sigaction()` instead, which [is](https://man7.org/linux/man-pages/man7/signal-safety.7.html) async-signal-safe, provides the functionality we need, and is apparently available on all Android versions because it is also used e.g. [here](7bf0736e13/library/std/src/sys/unix/stack_overflow.rs (L112-L114)).
This commit is contained in:
Manish Goregaokar 2021-10-05 12:52:42 -07:00 committed by GitHub
commit eb860987cf
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1 changed files with 13 additions and 3 deletions
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16
library/std/src/sys/unix/process/process_unix.rs
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@ -333,9 +333,19 @@ impl Command {
let mut set = MaybeUninit::<libc::sigset_t>::uninit();
cvt(sigemptyset(set.as_mut_ptr()))?;
cvt(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(), ptr::null_mut()))?;
let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
if ret == libc::SIG_ERR {
return Err(io::Error::last_os_error());
#[cfg(target_os = "android")] // see issue #88585
{
let mut action: libc::sigaction = mem::zeroed();
action.sa_sigaction = libc::SIG_DFL;
cvt(libc::sigaction(libc::SIGPIPE, &action, ptr::null_mut()))?;
}
#[cfg(not(target_os = "android"))]
{
let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
if ret == libc::SIG_ERR {
return Err(io::Error::last_os_error());
}
}
}