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Fix futex return values

This commit is contained in:
Ruihan Li 2025-10-06 23:22:42 +08:00 committed by Jianfeng Jiang
parent 52ddbeaff8
commit 43f50c5e2a
1 changed files with 18 additions and 24 deletions
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42
kernel/src/process/posix_thread/futex.rs
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@ -96,38 +96,32 @@ pub fn futex_wait_bitset(
);
}
let futex_id = futex_item.id;
futex_bucket.add_item(futex_item);
// Release the lock.
drop(futex_bucket);
let result = waiter.pause_timeout(&timeout.into());
if let Err(err) = &result {
if matches!(err.error(), Errno::EINTR | Errno::ETIME) {
// If the futex wait operation was interrupted by a signal or timed out, the
// `FutexItem` must be dequeued and dropped. Otherwise, malicious user programs
// could repeatedly issue futex wait operations to exhaust kernel memory.
//
// Due to asynchronicity, this removal can't be done by queue position nor by
// futex key match up:
// * The position might have changed during the pause as some earlier futex might
// have been dequeued
// * If two futexes with the same key are enqueued and then one of them times out
// or is interrupted, a removal by key would likely dequeue the wrong futex
//
// Therefore, we need to perform a removal by unique global futex ID.
futex_bucket_ref.lock().remove_by_id(futex_id);
// FIXME: If the futex is woken up and a signal comes at the same time, we should succeed
// instead of failing with `EINTR`. The code below is of course wrong, but was needed to
// make the gVisor tests happy. See <https://github.com/asterinas/asterinas/pull/1577>.
if err.error() == Errno::EINTR {
return Ok(());
}
}
// If the futex wait operation was interrupted by a signal or timed out, the
// `FutexItem` must be dequeued and dropped. Otherwise, malicious user programs
// could repeatedly issue futex wait operations to exhaust kernel memory.
let item = futex_bucket_ref.lock().remove_by_waker(&waiter.waker());
if item.is_none() {
// The futex item will be removed asynchronously if and only if it has been woken up. In
// that case, we should report success to the user.
// FIXME: `pause_timeout` should return `Ok(())` in this case, but it currently may return
// errors due to race conditions.
Ok(())
} else if let Err(err) = result {
Err(err)
} else {
// Spurious wakeups. Return `EINTR` anyway.
return_errno_with_message!(
Errno::EINTR,
"the current thread is interrupted by a signal"
);
}
result
}
pub fn futex_wake(futex_addr: Vaddr, max_count: usize, pid: Option<Pid>) -> Result<usize> {