diff --git a/kernel/src/arch/aarch64/irq/gic/gicd.rs b/kernel/src/arch/aarch64/irq/gic/gicd.rs
index 389bf4e..af34da0 100644
--- a/kernel/src/arch/aarch64/irq/gic/gicd.rs
+++ b/kernel/src/arch/aarch64/irq/gic/gicd.rs
@@ -1,5 +1,5 @@
 use crate::mem::virt::DeviceMemoryIo;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use tock_registers::interfaces::{Readable, Writeable};
 use tock_registers::registers::{ReadOnly, ReadWrite};
 use tock_registers::{register_bitfields, register_structs};
@@ -63,7 +63,7 @@ impl GicdSharedRegs {
 }
 
 pub(super) struct Gicd {
-    shared_regs: IrqSafeNullLock<DeviceMemoryIo<GicdSharedRegs>>,
+    shared_regs: IrqSafeSpinLock<DeviceMemoryIo<GicdSharedRegs>>,
     banked_regs: DeviceMemoryIo<GicdBankedRegs>,
 }
 
@@ -73,7 +73,7 @@ impl Gicd {
         banked_mmio: DeviceMemoryIo<GicdBankedRegs>,
     ) -> Self {
         Self {
-            shared_regs: IrqSafeNullLock::new(shared_mmio),
+            shared_regs: IrqSafeSpinLock::new(shared_mmio),
             banked_regs: banked_mmio,
         }
     }
diff --git a/kernel/src/arch/aarch64/irq/gic/mod.rs b/kernel/src/arch/aarch64/irq/gic/mod.rs
index e81175e..aa70f78 100644
--- a/kernel/src/arch/aarch64/irq/gic/mod.rs
+++ b/kernel/src/arch/aarch64/irq/gic/mod.rs
@@ -5,7 +5,7 @@ use crate::dev::{
     Device,
 };
 use crate::mem::virt::{DeviceMemory, DeviceMemoryIo};
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use error::Errno;
 
@@ -29,7 +29,7 @@ pub struct Gic {
     gicd_base: usize,
     gicc_base: usize,
     scheduler_irq: IrqNumber,
-    table: IrqSafeNullLock<[Option<&'static (dyn IntSource + Sync)>; MAX_IRQ]>,
+    table: IrqSafeSpinLock<[Option<&'static (dyn IntSource + Sync)>; MAX_IRQ]>,
 }
 
 impl IrqNumber {
@@ -94,7 +94,10 @@ impl IntController for Gic {
             let table = self.table.lock();
             match table[irq_number] {
                 None => panic!("No handler registered for irq{}", irq_number),
-                Some(handler) => handler.handle_irq().expect("irq handler failed"),
+                Some(handler) => {
+                    drop(table);
+                    handler.handle_irq().expect("irq handler failed")
+                },
             }
         }
 
@@ -132,7 +135,7 @@ impl Gic {
             gicd_base,
             gicc_base,
             scheduler_irq,
-            table: IrqSafeNullLock::new([None; MAX_IRQ]),
+            table: IrqSafeSpinLock::new([None; MAX_IRQ]),
         }
     }
 }
diff --git a/kernel/src/arch/aarch64/mach_orangepi3/gpio.rs b/kernel/src/arch/aarch64/mach_orangepi3/gpio.rs
index 048ffb1..06db644 100644
--- a/kernel/src/arch/aarch64/mach_orangepi3/gpio.rs
+++ b/kernel/src/arch/aarch64/mach_orangepi3/gpio.rs
@@ -10,7 +10,7 @@ use crate::dev::{
     Device,
 };
 use crate::mem::virt::DeviceMemoryIo;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use error::Errno;
 use tock_registers::interfaces::{Readable, Writeable};
@@ -33,7 +33,7 @@ struct CpuxGpio {
 }
 
 pub struct Gpio {
-    cpux: InitOnce<IrqSafeNullLock<CpuxGpio>>,
+    cpux: InitOnce<IrqSafeSpinLock<CpuxGpio>>,
     cpux_base: usize,
 }
 
@@ -144,7 +144,7 @@ impl Device for Gpio {
     }
 
     unsafe fn enable(&self) -> Result<(), Errno> {
-        self.cpux.init(IrqSafeNullLock::new(CpuxGpio {
+        self.cpux.init(IrqSafeSpinLock::new(CpuxGpio {
             regs: DeviceMemoryIo::map(self.name(), self.cpux_base, 1)?,
         }));
         Ok(())
diff --git a/kernel/src/arch/aarch64/mach_orangepi3/rtc.rs b/kernel/src/arch/aarch64/mach_orangepi3/rtc.rs
index 2ac5d54..0f75b49 100644
--- a/kernel/src/arch/aarch64/mach_orangepi3/rtc.rs
+++ b/kernel/src/arch/aarch64/mach_orangepi3/rtc.rs
@@ -5,7 +5,7 @@ use crate::dev::{
     Device,
 };
 use crate::mem::virt::DeviceMemoryIo;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use error::Errno;
 use tock_registers::{
@@ -47,7 +47,7 @@ register_structs! {
 }
 
 pub struct Rtc {
-    regs: InitOnce<IrqSafeNullLock<DeviceMemoryIo<Regs>>>,
+    regs: InitOnce<IrqSafeSpinLock<DeviceMemoryIo<Regs>>>,
     base: usize,
     irq: IrqNumber,
 }
@@ -90,7 +90,7 @@ impl Device for Rtc {
     }
 
     unsafe fn enable(&self) -> Result<(), Errno> {
-        self.regs.init(IrqSafeNullLock::new(DeviceMemoryIo::map(
+        self.regs.init(IrqSafeSpinLock::new(DeviceMemoryIo::map(
             self.name(),
             self.base,
             1,
diff --git a/kernel/src/arch/aarch64/mach_orangepi3/uart.rs b/kernel/src/arch/aarch64/mach_orangepi3/uart.rs
index df8dff6..a2641a2 100644
--- a/kernel/src/arch/aarch64/mach_orangepi3/uart.rs
+++ b/kernel/src/arch/aarch64/mach_orangepi3/uart.rs
@@ -5,7 +5,7 @@ use crate::dev::{
     Device,
 };
 use crate::mem::virt::DeviceMemoryIo;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use error::Errno;
 use tock_registers::interfaces::{ReadWriteable, Readable, Writeable};
@@ -77,7 +77,7 @@ struct UartInner {
 }
 
 pub(super) struct Uart {
-    inner: InitOnce<IrqSafeNullLock<UartInner>>,
+    inner: InitOnce<IrqSafeSpinLock<UartInner>>,
     base: usize,
     irq: IrqNumber,
 }
@@ -92,7 +92,7 @@ impl Device for Uart {
             regs: DeviceMemoryIo::map(self.name(), self.base, 1)?,
         };
         // TODO
-        self.inner.init(IrqSafeNullLock::new(inner));
+        self.inner.init(IrqSafeSpinLock::new(inner));
         Ok(())
     }
 }
diff --git a/kernel/src/arch/aarch64/mach_orangepi3/wdog.rs b/kernel/src/arch/aarch64/mach_orangepi3/wdog.rs
index f759205..3bca2dd 100644
--- a/kernel/src/arch/aarch64/mach_orangepi3/wdog.rs
+++ b/kernel/src/arch/aarch64/mach_orangepi3/wdog.rs
@@ -1,6 +1,6 @@
 use crate::dev::Device;
 use crate::mem::virt::DeviceMemoryIo;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use error::Errno;
 use tock_registers::{
@@ -39,7 +39,7 @@ register_structs! {
 }
 
 pub(super) struct RWdog {
-    inner: InitOnce<IrqSafeNullLock<DeviceMemoryIo<RWdogRegs>>>,
+    inner: InitOnce<IrqSafeSpinLock<DeviceMemoryIo<RWdogRegs>>>,
     base: usize,
 }
 
@@ -49,7 +49,7 @@ impl Device for RWdog {
     }
 
     unsafe fn enable(&self) -> Result<(), Errno> {
-        self.inner.init(IrqSafeNullLock::new(DeviceMemoryIo::map(
+        self.inner.init(IrqSafeSpinLock::new(DeviceMemoryIo::map(
             self.name(),
             self.base,
             1,
diff --git a/kernel/src/arch/aarch64/mach_rpi3/uart.rs b/kernel/src/arch/aarch64/mach_rpi3/uart.rs
index f7e059e..0ab4312 100644
--- a/kernel/src/arch/aarch64/mach_rpi3/uart.rs
+++ b/kernel/src/arch/aarch64/mach_rpi3/uart.rs
@@ -1,6 +1,6 @@
 use crate::dev::{serial::SerialDevice, Device};
 use crate::mem::virt::DeviceMemoryIo;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use error::Errno;
 use tock_registers::{
@@ -17,7 +17,7 @@ register_structs! {
 }
 
 pub(super) struct Bcm283xMiniUart {
-    regs: InitOnce<IrqSafeNullLock<DeviceMemoryIo<Regs>>>,
+    regs: InitOnce<IrqSafeSpinLock<DeviceMemoryIo<Regs>>>,
     base: usize,
 }
 
@@ -27,7 +27,7 @@ impl Device for Bcm283xMiniUart {
     }
 
     unsafe fn enable(&self) -> Result<(), Errno> {
-        self.regs.init(IrqSafeNullLock::new(DeviceMemoryIo::map(
+        self.regs.init(IrqSafeSpinLock::new(DeviceMemoryIo::map(
             self.name(),
             self.base,
             1,
diff --git a/kernel/src/dev/rtc/pl031.rs b/kernel/src/dev/rtc/pl031.rs
index ad025c0..cf6e6b6 100644
--- a/kernel/src/dev/rtc/pl031.rs
+++ b/kernel/src/dev/rtc/pl031.rs
@@ -6,7 +6,7 @@ use crate::dev::{
     Device,
 };
 use crate::mem::virt::DeviceMemoryIo;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use error::Errno;
 use tock_registers::{
@@ -49,7 +49,7 @@ struct Pl031Inner {
 
 /// Device struct for PL031
 pub struct Pl031 {
-    inner: InitOnce<IrqSafeNullLock<Pl031Inner>>,
+    inner: InitOnce<IrqSafeSpinLock<Pl031Inner>>,
     base: usize,
     irq: IrqNumber,
 }
@@ -88,7 +88,7 @@ impl Device for Pl031 {
         inner.regs.MR.set(inner.regs.DR.get() + 1);
         inner.regs.CR.modify(CR::RTCStart::SET);
 
-        self.inner.init(IrqSafeNullLock::new(inner));
+        self.inner.init(IrqSafeSpinLock::new(inner));
 
         Ok(())
     }
diff --git a/kernel/src/dev/serial/pl011.rs b/kernel/src/dev/serial/pl011.rs
index e9b8271..5d13d6e 100644
--- a/kernel/src/dev/serial/pl011.rs
+++ b/kernel/src/dev/serial/pl011.rs
@@ -7,7 +7,7 @@ use crate::dev::{
     Device,
 };
 use crate::mem::virt::DeviceMemoryIo;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use core::fmt;
 use error::Errno;
@@ -77,7 +77,7 @@ struct Pl011Inner {
 
 /// Device struct for PL011
 pub struct Pl011 {
-    inner: InitOnce<IrqSafeNullLock<Pl011Inner>>,
+    inner: InitOnce<IrqSafeSpinLock<Pl011Inner>>,
     base: usize,
     irq: IrqNumber,
 }
@@ -134,6 +134,7 @@ impl IntSource for Pl011 {
         inner.regs.ICR.write(ICR::ALL::CLEAR);
 
         let byte = inner.regs.DR.get();
+        drop(inner);
         debugln!("irq byte = {:#04x}", byte);
 
         Ok(())
@@ -176,7 +177,7 @@ impl Device for Pl011 {
         };
         inner.enable();
 
-        self.inner.init(IrqSafeNullLock::new(inner));
+        self.inner.init(IrqSafeSpinLock::new(inner));
 
         Ok(())
     }
diff --git a/kernel/src/mem/heap.rs b/kernel/src/mem/heap.rs
index 36011c6..539f8df 100644
--- a/kernel/src/mem/heap.rs
+++ b/kernel/src/mem/heap.rs
@@ -1,6 +1,6 @@
 //! Kernel heap allocation facilities
 
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use crate::util::InitOnce;
 use core::alloc::{GlobalAlloc, Layout};
 use core::ptr::null_mut;
@@ -49,7 +49,7 @@ fn alloc_error_handler(layout: Layout) -> ! {
 #[global_allocator]
 static SYSTEM_ALLOC: SystemAlloc = SystemAlloc;
 
-static HEAP: InitOnce<IrqSafeNullLock<Heap>> = InitOnce::new();
+static HEAP: InitOnce<IrqSafeSpinLock<Heap>> = InitOnce::new();
 
 /// Initializes kernel heap with virtual `base` address and `size`.
 ///
@@ -61,5 +61,5 @@ pub unsafe fn init(base: usize, size: usize) {
 
     infoln!("Kernel heap: {:#x}..{:#x}", base, base + size);
 
-    HEAP.init(IrqSafeNullLock::new(heap));
+    HEAP.init(IrqSafeSpinLock::new(heap));
 }
diff --git a/kernel/src/mem/phys/manager.rs b/kernel/src/mem/phys/manager.rs
index 3d34af5..09f574d 100644
--- a/kernel/src/mem/phys/manager.rs
+++ b/kernel/src/mem/phys/manager.rs
@@ -1,6 +1,6 @@
 use super::{PageInfo, PageUsage};
 use crate::mem::{virtualize, PAGE_SIZE};
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use core::mem;
 use error::Errno;
 
@@ -73,4 +73,4 @@ unsafe impl Manager for SimpleManager {
     }
 }
 
-pub(super) static MANAGER: IrqSafeNullLock<Option<SimpleManager>> = IrqSafeNullLock::new(None);
+pub(super) static MANAGER: IrqSafeSpinLock<Option<SimpleManager>> = IrqSafeSpinLock::new(None);
diff --git a/kernel/src/proc/mod.rs b/kernel/src/proc/mod.rs
index 576364f..5962ca8 100644
--- a/kernel/src/proc/mod.rs
+++ b/kernel/src/proc/mod.rs
@@ -1,7 +1,7 @@
 //! Process and thread manipulation facilities
 
 use crate::mem;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use alloc::{
     boxed::Box,
     collections::{BTreeMap},
@@ -42,8 +42,8 @@ pub fn switch() {
 }
 
 /// Global list of all processes in the system
-pub(self) static PROCESSES: IrqSafeNullLock<BTreeMap<Pid, ProcessRef>> =
-    IrqSafeNullLock::new(BTreeMap::new());
+pub(self) static PROCESSES: IrqSafeSpinLock<BTreeMap<Pid, ProcessRef>> =
+    IrqSafeSpinLock::new(BTreeMap::new());
 
 /// Sets up initial process and enters it.
 ///
diff --git a/kernel/src/proc/process.rs b/kernel/src/proc/process.rs
index 672c6c4..7400e74 100644
--- a/kernel/src/proc/process.rs
+++ b/kernel/src/proc/process.rs
@@ -5,7 +5,7 @@ use crate::mem::{
     virt::{MapAttributes, Space},
 };
 use crate::proc::{PROCESSES, SCHED};
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use alloc::rc::Rc;
 use core::cell::UnsafeCell;
 use core::fmt;
@@ -51,7 +51,7 @@ struct ProcessInner {
 #[allow(dead_code)]
 pub struct Process {
     ctx: UnsafeCell<Context>,
-    inner: IrqSafeNullLock<ProcessInner>,
+    inner: IrqSafeSpinLock<ProcessInner>,
 }
 
 impl From<i32> for ExitCode {
@@ -141,9 +141,6 @@ impl Process {
         proc.inner.lock().state = State::Running;
         let ctx = proc.ctx.get();
 
-        // I don't think this is bad: process can't be dropped fully unless
-        // it's been reaped (and this function won't run for such process)
-        drop(proc);
         (&mut *ctx).enter()
     }
 
@@ -171,10 +168,6 @@ impl Process {
         let src_ctx = src.ctx.get();
         let dst_ctx = dst.ctx.get();
 
-        // See "drop" note in Process::enter()
-        drop(src);
-        drop(dst);
-
         (&mut *src_ctx).switch(&mut *dst_ctx);
     }
 
@@ -188,7 +181,7 @@ impl Process {
         let id = Pid::new_kernel();
         let res = Rc::new(Self {
             ctx: UnsafeCell::new(Context::kernel(entry as usize, arg)),
-            inner: IrqSafeNullLock::new(ProcessInner {
+            inner: IrqSafeSpinLock::new(ProcessInner {
                 id,
                 exit: None,
                 space: None,
@@ -238,7 +231,6 @@ impl Process {
                 debugln!("r = {}", Rc::strong_count(&proc));
                 return Ok(r);
             } else {
-                drop(proc);
                 cortex_a::asm::wfi();
             }
         }
@@ -312,7 +304,6 @@ impl Process {
 
             drop(lock);
 
-            drop(proc);
             (*ctx).enter();
         }
     }
diff --git a/kernel/src/proc/sched.rs b/kernel/src/proc/sched.rs
index 3f2f598..2700fba 100644
--- a/kernel/src/proc/sched.rs
+++ b/kernel/src/proc/sched.rs
@@ -1,7 +1,7 @@
 //!
 use crate::proc::{Pid, Process, ProcessRef, PROCESSES};
 use crate::util::InitOnce;
-use crate::sync::IrqSafeNullLock;
+use crate::sync::IrqSafeSpinLock;
 use alloc::{rc::Rc, collections::VecDeque};
 
 struct SchedulerInner {
@@ -12,7 +12,7 @@ struct SchedulerInner {
 
 /// Process scheduler state and queues
 pub struct Scheduler {
-    inner: InitOnce<IrqSafeNullLock<SchedulerInner>>,
+    inner: InitOnce<IrqSafeSpinLock<SchedulerInner>>,
 }
 
 impl SchedulerInner {
@@ -35,7 +35,7 @@ impl Scheduler {
     /// * idle thread
     /// * process list/queue data structs
     pub fn init(&self) {
-        self.inner.init(IrqSafeNullLock::new(SchedulerInner::new()));
+        self.inner.init(IrqSafeSpinLock::new(SchedulerInner::new()));
     }
 
     /// Schedules a thread for execution
diff --git a/kernel/src/sync.rs b/kernel/src/sync.rs
index 5022ad0..4361065 100644
--- a/kernel/src/sync.rs
+++ b/kernel/src/sync.rs
@@ -1,63 +1,84 @@
 //! Synchronization facilities module
 
 use crate::arch::platform::{irq_mask_save, irq_restore};
+use core::sync::atomic::{AtomicBool, Ordering};
 use core::cell::UnsafeCell;
 use core::ops::{Deref, DerefMut};
 
 /// Lock structure ensuring IRQs are disabled when inner value is accessed
-pub struct IrqSafeNullLock<T: ?Sized> {
+pub struct IrqSafeSpinLock<T> {
     value: UnsafeCell<T>,
+    state: AtomicBool
 }
 
-/// Guard-structure wrapping a reference to value owned by [IrqSafeNullLock].
+/// Guard-structure wrapping a reference to value owned by [IrqSafeSpinLock].
 /// Restores saved IRQ state when dropped.
-pub struct IrqSafeNullLockGuard<'a, T: ?Sized> {
-    value: &'a mut T,
+pub struct IrqSafeSpinLockGuard<'a, T> {
+    lock: &'a IrqSafeSpinLock<T>,
     irq_state: u64,
 }
 
-impl<T> IrqSafeNullLock<T> {
+impl<T> IrqSafeSpinLock<T> {
     /// Constructs a new instance of the lock, wrapping `value`
     #[inline(always)]
     pub const fn new(value: T) -> Self {
         Self {
             value: UnsafeCell::new(value),
+            state: AtomicBool::new(false)
         }
     }
 
-    /// Returns [IrqSafeNullLockGuard] for this lock
+    #[inline(always)]
+    fn try_lock(&self) -> Result<bool, bool> {
+        self.state.compare_exchange_weak(false, true, Ordering::Acquire, Ordering::Relaxed)
+    }
+
+    #[inline(always)]
+    unsafe fn force_release(&self) {
+        self.state.store(false, Ordering::Release);
+        cortex_a::asm::sev();
+    }
+
+    /// Returns [IrqSafeSpinLockGuard] for this lock
     #[inline]
-    pub fn lock(&self) -> IrqSafeNullLockGuard<T> {
+    pub fn lock(&self) -> IrqSafeSpinLockGuard<T> {
+        let irq_state = unsafe { irq_mask_save() };
+
+        while self.try_lock().is_err() {
+            cortex_a::asm::wfe();
+        }
+
         unsafe {
-            IrqSafeNullLockGuard {
-                value: &mut *self.value.get(),
-                irq_state: irq_mask_save(),
+            IrqSafeSpinLockGuard {
+                lock: self,
+                irq_state
             }
         }
     }
 }
 
-impl<T: ?Sized> Deref for IrqSafeNullLockGuard<'_, T> {
+impl<T> Deref for IrqSafeSpinLockGuard<'_, T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
-        self.value
+        unsafe { &*self.lock.value.get() }
     }
 }
 
-impl<T: ?Sized> DerefMut for IrqSafeNullLockGuard<'_, T> {
+impl<T> DerefMut for IrqSafeSpinLockGuard<'_, T> {
     fn deref_mut(&mut self) -> &mut Self::Target {
-        self.value
+        unsafe { &mut *self.lock.value.get() }
     }
 }
 
-impl<T: ?Sized> Drop for IrqSafeNullLockGuard<'_, T> {
+impl<T> Drop for IrqSafeSpinLockGuard<'_, T> {
     #[inline(always)]
     fn drop(&mut self) {
         unsafe {
+            self.lock.force_release();
             irq_restore(self.irq_state);
         }
     }
 }
 
-unsafe impl<T: ?Sized> Sync for IrqSafeNullLock<T> {}
+unsafe impl<T> Sync for IrqSafeSpinLock<T> {}