diff --git a/arch/x86_64/mem.c b/arch/x86_64/mem.c
index 462efd5..2753850 100644
--- a/arch/x86_64/mem.c
+++ b/arch/x86_64/mem.c
@@ -1,4 +1,3 @@
-#include <zinnia/types.h>
 #include <arch/mem.h>
 #include <stddef.h>
 #include <stdint.h>
diff --git a/arch/x86_64/meson.build b/arch/x86_64/meson.build
index b73eb4f..bdb743b 100644
--- a/arch/x86_64/meson.build
+++ b/arch/x86_64/meson.build
@@ -14,7 +14,6 @@ kernel_sources += files(
     'mem.c',
     'percpu.c',
     'pmap.c',
-    'pmap.c',
     'random.c',
     'sched.c',
     'serial.c',
diff --git a/arch/x86_64/sched.c b/arch/x86_64/sched.c
index 1bfc345..f2cfbd2 100644
--- a/arch/x86_64/sched.c
+++ b/arch/x86_64/sched.c
@@ -11,6 +11,7 @@
 #include <bits/sched.h>
 #include <stddef.h>
 #include <stdint.h>
+#include <string.h>
 #include <x86_64/apic.h>
 #include <x86_64/asm.h>
 #include <x86_64/defs.h>
@@ -93,6 +94,11 @@ struct task* arch_sched_switch(struct task* from, struct task* to) {
     return perform_switch(&from_ctx->rsp, to_ctx->rsp, from);
 }
 
+constexpr size_t FPU_FCW_OFFSET = 0;
+constexpr size_t FPU_MXCSR_OFFSET = 24;
+constexpr uint16_t FPU_DEFAULT_FCW = 0x37F;
+constexpr uint32_t FPU_DEFAULT_MXCSR = 0x1F80;
+
 // Calls task_entry with the correct parameters.
 [[__naked]]
 void task_entry_thunk() {
@@ -142,6 +148,11 @@ errno_t arch_task_init(
         context->fpu_region = (void*)fpu_base;
         context->fpu_phys = pages;
 
+        const uint16_t fcw = FPU_DEFAULT_FCW;
+        const uint32_t mxcsr = FPU_DEFAULT_MXCSR;
+        memcpy((uint8_t*)fpu_base + FPU_FCW_OFFSET, &fcw, sizeof(fcw));
+        memcpy((uint8_t*)fpu_base + FPU_MXCSR_OFFSET, &mxcsr, sizeof(mxcsr));
+
         context->ds = asm_read_ds();
         context->es = asm_read_es();
         context->fs = asm_read_fs();
diff --git a/arch/x86_64/smp.c b/arch/x86_64/smp.c
index 7feebc1..ccc36bb 100644
--- a/arch/x86_64/smp.c
+++ b/arch/x86_64/smp.c
@@ -148,7 +148,7 @@ static void smp_trampoline() {
           [kernel64_cs] "i"(offsetof(struct gdt, kernel_code64)),
           [kernel64_ds] "i"(offsetof(struct gdt, kernel_data64)),
           [cr0] "i"(CR0_PE | CR0_ET),
-          [cr0_pg] "i"(CR0_PG),
+          [cr0_pg] "i"((uint32_t)CR0_PG),
           [cr4_pae] "i"(CR4_PAE),
           [msr_efer] "i"(MSR_EFER),
           [efer_lme] "i"(MSR_EFER_LME),
diff --git a/core/spin.c b/core/spin.c
index 8cfac39..24d7897 100644
--- a/core/spin.c
+++ b/core/spin.c
@@ -17,6 +17,16 @@ void spin_lock(struct spinlock* spin) {
     }
 }
 
+bool spin_trylock(struct spinlock* spin) {
+    irq_lock();
+    uint32_t owner = atomic_load(&spin->owner, ATOMIC_RELAXED);
+    uint32_t expected = owner;
+    if (atomic_compare_exchange(&spin->next, &expected, owner + 1, ATOMIC_ACQUIRE, ATOMIC_RELAXED))
+        return true;
+    irq_unlock();
+    return false;
+}
+
 void spin_unlock(struct spinlock* spin) {
     uint32_t val = atomic_load(&spin->owner, ATOMIC_RELAXED);
     atomic_store(&spin->owner, val + 1, ATOMIC_RELEASE);
diff --git a/fs/vfs/ident.c b/fs/vfs/ident.c
index 24cf39d..5106fa3 100644
--- a/fs/vfs/ident.c
+++ b/fs/vfs/ident.c
@@ -5,3 +5,13 @@ static const struct ident kernel_identity = {0};
 const struct ident* ident_kernel() {
     return &kernel_identity;
 }
+
+bool ident_in_group(const struct ident* identity, gid_t gid, bool use_real) {
+    if (gid == (use_real ? identity->gid : identity->egid))
+        return true;
+    vec_foreach(&identity->groups, i) {
+        if (vec_elem_get(&identity->groups, i) == gid)
+            return true;
+    }
+    return false;
+}
diff --git a/include/zinnia/ident.h b/include/zinnia/ident.h
index 7fd3ee1..b064716 100644
--- a/include/zinnia/ident.h
+++ b/include/zinnia/ident.h
@@ -11,3 +11,5 @@ struct ident {
 };
 
 const struct ident* ident_kernel(void);
+
+bool ident_in_group(const struct ident* identity, gid_t gid, bool use_real);
diff --git a/include/zinnia/list.h b/include/zinnia/list.h
index d7c2114..9a8c025 100644
--- a/include/zinnia/list.h
+++ b/include/zinnia/list.h
@@ -10,7 +10,7 @@
         type _sl_link; \
     }
 
-#define list_is_empty(head)   ((head)->_sl_head == NULL)
+#define list_is_empty(head)   ((head)->_sl_head == nullptr)
 #define list_first(head)      ((head)->_sl_head)
 #define list_next(elm, field) ((elm)->field._sl_link)
 
diff --git a/include/zinnia/refcount.h b/include/zinnia/refcount.h
index d1ede0f..7469cb2 100644
--- a/include/zinnia/refcount.h
+++ b/include/zinnia/refcount.h
@@ -16,6 +16,15 @@ static inline void refcount_inc(struct refcount* rc) {
     atomic_fetch_add(&rc->count, 1, ATOMIC_RELAXED);
 }
 
+static inline bool refcount_inc_not_zero(struct refcount* rc) {
+    size_t count = atomic_load(&rc->count, ATOMIC_RELAXED);
+    do {
+        if (count == 0)
+            return false;
+    } while (!atomic_compare_exchange_weak(&rc->count, &count, count + 1, ATOMIC_ACQUIRE, ATOMIC_RELAXED));
+    return true;
+}
+
 static inline bool refcount_dec(struct refcount* rc) {
     if (atomic_fetch_sub(&rc->count, 1, ATOMIC_RELEASE) != 1)
         return false;
diff --git a/include/zinnia/spin.h b/include/zinnia/spin.h
index 810e7ae..f513534 100644
--- a/include/zinnia/spin.h
+++ b/include/zinnia/spin.h
@@ -14,5 +14,7 @@ void spin_init(struct spinlock* spin);
 // Attempts to lock a spinlock. If it's already locked, waits until it's freed.
 void spin_lock(struct spinlock* spin);
 
+bool spin_trylock(struct spinlock* spin);
+
 // Unlocks a spinlock.
 void spin_unlock(struct spinlock* spin);