mirror/moss-kernel
1
0
Fork 0
mirror of https://github.com/hexagonal-sun/moss-kernel.git synced 2026-04-18 14:19:01 -04:00
Code Issues Packages Projects Releases Wiki Activity

get data w/ spinlock

Browse Source
This commit is contained in:
Ashwin Naren
2025-12-18 14:46:33 -08:00
parent cb6dbdf5bb
commit 93df6b0ebc
1 changed files with 16 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
src/process/threading.rs
View File

@@ -81,13 +81,15 @@ pub async fn sys_futex(
match cmd {
FUTEX_WAIT => {
// Fail fast if the value has already changed
let current: u32 = copy_from_user(uaddr).await?;
if current != val {
return Err(KernelError::TryAgain);
}
// Ensure the wait-queue exists *before* we begin checking the
// futex word so that a racing FUTEX_WAKE cannot miss us. This
// avoids the classic lost-wake-up race where a waker runs between
// our value check and queue insertion.
//
// After publishing the queue we perform a second sanity check on
// the user word, mirroring Linux’s “double read” strategy.
// Obtain (or create) the wait-queue for this futex word
// Obtain (or create) the wait-queue for this futex word.
let table = FUTEX_TABLE.get_or_init(|| SpinLock::new(BTreeMap::new()));
let waitq_arc = {
let mut guard = table.lock_save_irq();
@@ -97,6 +99,14 @@ pub async fn sys_futex(
.clone()
};
// First read – may fault and therefore is done outside the lock.
let current: u32 = copy_from_user(uaddr).await?;
if current != val {
return Err(KernelError::TryAgain);
}
// Second read – ensures the value is still what we expect *after*
// the wait-queue entry is visible to other threads.
if copy_from_user(uaddr).await? != val {
return Err(KernelError::TryAgain);
}