From: Matt Corallo Date: Sun, 8 Sep 2024 19:05:28 +0000 (+0000) Subject: Simplify and fix `AtomicCounter` X-Git-Url: http://git.bitcoin.ninja/?a=commitdiff_plain;h=2ab133d432289ca00bfd0d56f650e2e45f515a70;p=rust-lightning Simplify and fix `AtomicCounter` `AtomicCounter` was slightly race-y on 32-bit platforms because it increments the high `AtomicUsize` independently from the low `AtomicUsize`, leading to a potential race where another thread could observe the low increment but not the high increment and see a value of 0 twice. This isn't a big deal because (a) most platforms are 64-bit these days, (b) 32-bit platforms aren't super likely to have their counter overflow 32 bits anyway, and (c) the two writes are back-to-back so having another thread read during that window is very unlikely. However, we can also optimize the counter somewhat by using the `target_has_atomic = "64"` cfg flag, which we do here, allowing us to use `AtomicU64` even on 32-bit platforms where 64-bit atomics are available. This changes some test behavior slightly, which requires adaptation. Fixes #3000 --- diff --git a/lightning/src/ln/functional_tests.rs b/lightning/src/ln/functional_tests.rs index 22b7df1ed..03edb4c1b 100644 --- a/lightning/src/ln/functional_tests.rs +++ b/lightning/src/ln/functional_tests.rs @@ -7668,8 +7668,8 @@ fn test_bump_penalty_txn_on_revoked_htlcs() { assert_ne!(node_txn[0].input[0].previous_output, node_txn[2].input[0].previous_output); assert_ne!(node_txn[1].input[0].previous_output, node_txn[2].input[0].previous_output); - assert_eq!(node_txn[0].input[0].previous_output, revoked_htlc_txn[1].input[0].previous_output); - assert_eq!(node_txn[1].input[0].previous_output, revoked_htlc_txn[0].input[0].previous_output); + assert_eq!(node_txn[1].input[0].previous_output, revoked_htlc_txn[1].input[0].previous_output); + assert_eq!(node_txn[0].input[0].previous_output, revoked_htlc_txn[0].input[0].previous_output); // node_txn[3] spends the revoked outputs from the revoked_htlc_txn (which only have one // output, checked above). diff --git a/lightning/src/ln/monitor_tests.rs b/lightning/src/ln/monitor_tests.rs index 200e5ed84..8854d868a 100644 --- a/lightning/src/ln/monitor_tests.rs +++ b/lightning/src/ln/monitor_tests.rs @@ -2251,6 +2251,10 @@ fn do_test_restored_packages_retry(check_old_monitor_retries_after_upgrade: bool let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs); + // Reset our RNG counters to mirror the RNG output from when this test was written. + nodes[0].keys_manager.backing.inner.entropy_source.set_counter(0x1_0000_0004); + nodes[1].keys_manager.backing.inner.entropy_source.set_counter(0x1_0000_0004); + // Open a channel, lock in an HTLC, and immediately broadcast the commitment transaction. This // ensures that the HTLC timeout package is held until we reach its expiration height. let (_, _, chan_id, funding_tx) = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100_000, 50_000_000); diff --git a/lightning/src/sign/mod.rs b/lightning/src/sign/mod.rs index 890c1bc0f..1a84caf36 100644 --- a/lightning/src/sign/mod.rs +++ b/lightning/src/sign/mod.rs @@ -1853,6 +1853,9 @@ pub struct KeysManager { channel_master_key: Xpriv, channel_child_index: AtomicUsize, + #[cfg(test)] + pub(crate) entropy_source: RandomBytes, + #[cfg(not(test))] entropy_source: RandomBytes, seed: [u8; 32], @@ -2309,6 +2312,9 @@ impl SignerProvider for KeysManager { /// Switching between this struct and [`KeysManager`] will invalidate any previously issued /// invoices and attempts to pay previous invoices will fail. pub struct PhantomKeysManager { + #[cfg(test)] + pub(crate) inner: KeysManager, + #[cfg(not(test))] inner: KeysManager, inbound_payment_key: KeyMaterial, phantom_secret: SecretKey, @@ -2487,6 +2493,13 @@ impl RandomBytes { pub fn new(seed: [u8; 32]) -> Self { Self { seed, index: AtomicCounter::new() } } + + #[cfg(test)] + /// Force the counter to a value to produce the same output again. Mostly useful in tests where + /// we need to maintain behavior with a previous version which didn't use as much RNG output. + pub(crate) fn set_counter(&self, count: u64) { + self.index.set_counter(count); + } } impl EntropySource for RandomBytes { diff --git a/lightning/src/util/atomic_counter.rs b/lightning/src/util/atomic_counter.rs index d2e014113..bb2dbc0f7 100644 --- a/lightning/src/util/atomic_counter.rs +++ b/lightning/src/util/atomic_counter.rs @@ -1,32 +1,44 @@ -//! A simple atomic counter that uses AtomicUsize to give a u64 counter. +//! A simple atomic counter that uses mutexes if the platform doesn't support atomic u64s. -#[cfg(not(any(target_pointer_width = "32", target_pointer_width = "64")))] -compile_error!("We need at least 32-bit pointers for atomic counter (and to have enough memory to run LDK)"); +#[cfg(target_has_atomic = "64")] +use core::sync::atomic::{AtomicU64, Ordering}; +#[cfg(not(target_has_atomic = "64"))] +use crate::sync::Mutex; -use core::sync::atomic::{AtomicUsize, Ordering}; - -#[derive(Debug)] pub(crate) struct AtomicCounter { - // Usize needs to be at least 32 bits to avoid overflowing both low and high. If usize is 64 - // bits we will never realistically count into high: - counter_low: AtomicUsize, - counter_high: AtomicUsize, + #[cfg(target_has_atomic = "64")] + counter: AtomicU64, + #[cfg(not(target_has_atomic = "64"))] + counter: Mutex, } impl AtomicCounter { pub(crate) fn new() -> Self { Self { - counter_low: AtomicUsize::new(0), - counter_high: AtomicUsize::new(0), + #[cfg(target_has_atomic = "64")] + counter: AtomicU64::new(0), + #[cfg(not(target_has_atomic = "64"))] + counter: Mutex::new(0), } } pub(crate) fn get_increment(&self) -> u64 { - let low = self.counter_low.fetch_add(1, Ordering::AcqRel) as u64; - let high = if low == 0 { - self.counter_high.fetch_add(1, Ordering::AcqRel) as u64 - } else { - self.counter_high.load(Ordering::Acquire) as u64 - }; - (high << 32) | low + #[cfg(target_has_atomic = "64")] { + self.counter.fetch_add(1, Ordering::AcqRel) + } + #[cfg(not(target_has_atomic = "64"))] { + let mut mtx = self.counter.lock().unwrap(); + *mtx += 1; + *mtx - 1 + } + } + #[cfg(test)] + pub(crate) fn set_counter(&self, count: u64) { + #[cfg(target_has_atomic = "64")] { + self.counter.store(count, Ordering::Release); + } + #[cfg(not(target_has_atomic = "64"))] { + let mut mtx = self.counter.lock().unwrap(); + *mtx = count; + } } }