1 // SPDX-License-Identifier: GPL-2.0 2 3 //! RCU support. 4 //! 5 //! C header: [`include/linux/rcupdate.h`](srctree/include/linux/rcupdate.h) 6 7 use crate::{bindings, types::NotThreadSafe}; 8 9 /// Evidence that the RCU read side lock is held on the current thread/CPU. 10 /// 11 /// The type is explicitly not `Send` because this property is per-thread/CPU. 12 /// 13 /// # Invariants 14 /// 15 /// The RCU read side lock is actually held while instances of this guard exist. 16 pub struct Guard(NotThreadSafe); 17 18 impl Guard { 19 /// Acquires the RCU read side lock and returns a guard. 20 #[inline] 21 pub fn new() -> Self { 22 // SAFETY: An FFI call with no additional requirements. 23 unsafe { bindings::rcu_read_lock() }; 24 // INVARIANT: The RCU read side lock was just acquired above. 25 Self(NotThreadSafe) 26 } 27 28 /// Explicitly releases the RCU read side lock. 29 #[inline] 30 pub fn unlock(self) {} 31 } 32 33 impl Default for Guard { 34 #[inline] 35 fn default() -> Self { 36 Self::new() 37 } 38 } 39 40 impl Drop for Guard { 41 #[inline] 42 fn drop(&mut self) { 43 // SAFETY: By the type invariants, the RCU read side is locked, so it is ok to unlock it. 44 unsafe { bindings::rcu_read_unlock() }; 45 } 46 } 47 48 /// Acquires the RCU read side lock. 49 #[inline] 50 pub fn read_lock() -> Guard { 51 Guard::new() 52 } 53