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mm/zone: add hardening features

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Loïc Grégoire
2026-07-04 23:43:57 -04:00
parent 2d18761822
commit 79b96ed3dc
1 changed files with 160 additions and 68 deletions
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src/mm/zone.zig
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@@ -1,38 +1,84 @@
//! Slab allocator implementation with per-CPU object caching. //! Slab allocator implementation with per-CPU object caching.
//! Roughly based on XNU's zone allocator, which itself is based on FreeBSD's UMA. //! Roughly based on XNU's zone allocator, which itself is based on FreeBSD's
//! First described in Jeff Bonwick's "The Slab Allocator: An Object-Caching Kernel Memory Allocator" //! UMA. First described in Jeff Bonwick's "The Slab Allocator: An
//! and "Magazines and Vmem: Extending the Slab Allocator to Many CPUs and Arbitrary Resources", both from Solaris. //! Object-Caching Kernel Memory Allocator" and "Magazines and Vmem: Extending
//! the Slab Allocator to Many CPUs and Arbitrary Resources", both from Solaris.
//! //!
//! ## Structure
//! ----------------
//! The allocator is split in three layers: //! The allocator is split in three layers:
//! 1. Per-CPU layer //! 1. Per-CPU layer
//! 2. Zone depot layer //! 2. Zone depot layer
//! 3. Slab layer //! 3. Slab layer
//! Both (1) and (2) rely on so-called "magazines", an array of (constructed) objects that is either loaded in the CPU or sits in a *depot*, //! Both (1) and (2) rely on so-called "magazines", an array of (constructed)
//! a collection of magazines. //! objects that is either loaded in the CPU or sits in a *depot*, a collection
//! Each depot maintains full and empty magazine lists used to satisfy magazine allocation requests. //! of magazines. Each depot maintains full and empty magazine lists used to
//! satisfy magazine allocation requests.
//! //!
//! ## Per-CPU layer //! ## Per-CPU layer
//! Each CPU has an `alloc` and `free` magazine, where objects are allocated from and freed to, respectively. //! ----------------
//! This separation avoids hysteresis and might prove useful in the future for safe memory reclamation mechanisms (see FreeBSD GUS or XNU SMR). //! Each CPU has an `alloc` and `free` magazine, where objects are allocated
//! When one side runs dry/full, the magazines may be swapped. //! from and freed to, respectively. This separation avoids hysteresis and might
//! Each CPU also has its own depot, from which it allocates and frees its magazines to first. If there is //! prove useful in the future for safe memory reclamation mechanisms (see
//! no magazine in the local depot, the magazine will be provided from the zone depot layer. We keep track of the size of the depot //! FreeBSD GUS or XNU SMR). When one side runs dry/full, the magazines may be
//! and grow or shrink it according to configured limits (by default 128 KiB of memory is allowed to be kept around for each CPU) and //! swapped.
//! using a weighted moving average (WMA) based on the contention on the zone depot's lock; if contention is determined to be too high, //! Each CPU also has its own depot, from which it allocates and frees its
//! the CPU's depot is grown as to avoid falling back onto the zone depot too much. //! magazines to first. If there is no magazine in the local depot, the magazine
//! will be provided from the zone depot layer. We keep track of the size of the
//! depot and grow or shrink it according to configured limits (by default
//! 128 KiB of memory is allowed to be kept around for each CPU) and using a
//! weighted moving average (WMA) based on the contention on the zone depot's
//! lock; if contention is determined to be too high, the CPU's depot is grown
//! as to avoid falling back onto the zone depot too much.
//! //!
//! ## Zone depot layer //! ## Zone depot layer
//! The zone depot layer serves as a fallback when no magazines are available in the per-CPU depot, its size is managed through //! -------------------
//! a working-set size algorithm that uses the WMA of the minimum required magazines in an update window. Moving between the zone depot //! The zone depot layer serves as a fallback when no magazines are available in
//! layer and the per-CPU layer is done in batches as to avoid overly holding the zone depot lock and satisfy the desired per-CPU depot size. //! the per-CPU depot, its size is managed through a working-set size algorithm
//! that uses the WMA of the minimum required magazines in an update window.
//! Moving between the zone depot layer and the per-CPU layer is done in batches
//! as to avoid overly holding the zone depot lock and satisfy the desired
//! per-CPU depot size.
//! //!
//! ## Slab layer //! ## Slab layer
//! The slab layer is the fallback when all previous layers failed. A slab represents a contiguous chunk of memory holding //! -------------
//! a fixed number of constructed objects, determined when the zone is created, and is allocated via the kernel's virtual memory allocator. //! The slab layer is the fallback when all previous layers failed. A slab
//! Allocation in the slab is managed by a bitmap and slab metadata is retrieved through the `mm.Page` structure representing the page of allocated memory. //! represents a contiguous chunk of memory holding a fixed number of constructed
//! objects, determined when the zone is created, and is allocated via the
//! kernel's virtual memory allocator. Allocation in the slab is managed by a
//! bitmap and slab metadata is retrieved through the `mm.Page` structure
//! representing the page of allocated memory.
//!
//! ## Hardening features
//! ---------------------
//! Some basic hardening features are implemented in the allocator. Firstly,
//! all allocations are done in a FIFO manner as to annoy attackers which might
//! try exploiting double-free or use-after-free bugs (which shouldn't happen
//! since I never write bugs :^)).
//! For example, consider this use-after-free sequence in a LIFO allocator:
//! 1. Dangling pointer to A (oops!)
//! 2. free A
//! 3. alloc B
//! 4. The dangling pointer to A and B now point to the same address.
//!
//! For a double free scenario, an exploit would look like this:
//! 1. free A
//! 2. alloc B -> B points to the last freed address (A)
//! 3. free A (oops!)
//! 4. alloc C -> C points to the last freed address (A)
//! 5. Both C and B now point to the same address.
//!
//! Doing things in a FIFO way makes things less predictable but might incur
//! performance degradation as older elements may be colder in cache),so this
//! policy can be disabled changing a Zone's reuse policy on creation.
//! Additionally, heap poisoning can be enabled via a compile-time zonfig
//! option, `slab_poison` will only poison objects (potentially detecting the
//! use of uninitialized memory), and `slab_check_poison` will actively enforce
//! that the poison data is still intact inside an object, detecting
//! use-after-free bugs.
//! //!
//! ## Extra notes //! ## Extra notes
//! //! ---------------------
//! With poisoning enabled, constructors run when an object is allocated and //! With poisoning enabled, constructors run when an object is allocated and
//! destructors run when it is freed. Without poisoning, constructors run once //! destructors run when it is freed. Without poisoning, constructors run once
//! when the slab is created and destructors run when the slab is destroyed. //! when the slab is created and destructors run when the slab is destroyed.
@@ -120,8 +166,14 @@ const Slab = struct {
capacity: u16, capacity: u16,
/// Base address of the slab + its color. /// Base address of the slab + its color.
base: usize, base: usize,
/// Base address of the slab allocation. /// Color that was added to the base.
buf: usize, color: u16,
/// Round-robin cursor that is used to allocate objects from.
/// This is used to avoid predictable heap behavior; an attacker
/// will have more trouble exploiting double-free and use-after-free
/// bugs (as if anyone would try exploiting this :p).
alloc_rr: u16,
pub fn bitmap(self: *Slab) [*]u64 { pub fn bitmap(self: *Slab) [*]u64 {
return @ptrFromInt(@intFromPtr(self) + @sizeOf(Slab)); return @ptrFromInt(@intFromPtr(self) + @sizeOf(Slab));
@@ -134,18 +186,34 @@ const Slab = struct {
/// Allocates a free bit from the bitmap, returns the allocated bit. /// Allocates a free bit from the bitmap, returns the allocated bit.
pub fn bitmap_alloc(self: *Slab) ?u16 { pub fn bitmap_alloc(self: *Slab) ?u16 {
const bitmaps = std.mem.alignForward(usize, self.capacity, 64) / 64; const bitmaps = std.mem.alignForward(usize, self.capacity, 64) / 64;
for (0..bitmaps) |i| { const start_word = self.alloc_rr / 64;
const chunk = self.bitmap()[i]; const start_bit = self.alloc_rr % 64;
if (chunk == 0) continue; const low_mask: u64 = (@as(u64, 1) << @intCast(start_bit)) - 1;
const bit = @ctz(chunk);
self.bitmap()[i] &= ~(@as(u64, 1) << @intCast(bit)); for (0..bitmaps) |i| {
return @intCast((i * 64) + bit); const word_idx = (start_word + i) % bitmaps;
var chunk = self.bitmap()[word_idx];
// Skip the bits behind the cursor on the first word we check.
if (i == 0) chunk &= ~low_mask;
if (chunk == 0) continue;
return self.take_bit(word_idx, @ctz(chunk));
} }
// Wrap around, check the bits behind the cursor that we skipped.
const chunk = self.bitmap()[start_word] & low_mask;
if (chunk != 0) return self.take_bit(start_word, @ctz(chunk));
return null; return null;
} }
fn take_bit(self: *Slab, word_idx: usize, bit: anytype) u16 {
self.bitmap()[word_idx] &= ~(@as(u64, 1) << @intCast(bit));
const allocated: u16 = @intCast(word_idx * 64 + bit);
self.alloc_rr = if (allocated + 1 >= self.capacity) 0 else allocated + 1;
return allocated;
}
/// Free a bit to the bitmap. /// Free a bit to the bitmap.
pub fn bitmap_free(self: *Slab, idx: usize) void { pub fn bitmap_free(self: *Slab, idx: usize) void {
const bm = self.bitmap(); const bm = self.bitmap();
@@ -220,7 +288,8 @@ const Magazine = struct {
const MagazineList = struct { const MagazineList = struct {
/// List of magazines. /// List of magazines.
list: ?*Magazine, head: ?*Magazine,
tail: ?*Magazine,
/// Number of magazines. /// Number of magazines.
num: usize, num: usize,
/// Minimum since last update /// Minimum since last update
@@ -229,20 +298,37 @@ const MagazineList = struct {
wma: usize, wma: usize,
}; };
const ReusePolicy = enum {
LIFO,
FIFO,
};
const Depot = struct { const Depot = struct {
empty_mags: MagazineList, empty_mags: MagazineList,
full_mags: MagazineList, full_mags: MagazineList,
fn maglist_alloc(list: *MagazineList) ?*Magazine { fn maglist_alloc(list: *MagazineList) ?*Magazine {
const ret = list.list orelse return null; const ret = list.head orelse return null;
list.list = ret.next; list.head = ret.next;
if (list.head == null) list.tail = null;
ret.next = null;
return ret; return ret;
} }
fn maglist_free(list: *MagazineList, mag: *Magazine) void { fn maglist_free(list: *MagazineList, mag: *Magazine, policy: ReusePolicy) void {
mag.next = list.list; mag.next = null;
list.list = mag;
if (policy == .FIFO) {
if (list.tail) |tail| {
tail.next = mag;
} else {
list.head = mag;
}
list.tail = mag;
} else {
list.head = mag;
}
} }
fn alloc(maglist: *MagazineList) ?*Magazine { fn alloc(maglist: *MagazineList) ?*Magazine {
@@ -254,8 +340,8 @@ const Depot = struct {
return ret; return ret;
} }
fn free(mag: *Magazine, maglist: *MagazineList) void { fn free(mag: *Magazine, maglist: *MagazineList, policy: ReusePolicy) void {
maglist_free(maglist, mag); maglist_free(maglist, mag, policy);
maglist.num += 1; maglist.num += 1;
} }
}; };
@@ -334,7 +420,7 @@ pub const Zone = struct {
/// Size of objects in this zone. /// Size of objects in this zone.
obj_size: usize, obj_size: usize,
/// Alignment of objects in this zone. /// Alignment of objects in this zone.
alignment: usize, alignment: u16,
/// Size of a slab. /// Size of a slab.
slab_size: usize, slab_size: usize,
/// Size of a chunk. /// Size of a chunk.
@@ -342,9 +428,9 @@ pub const Zone = struct {
/// Offset for buf-to-bufctl conversion. /// Offset for buf-to-bufctl conversion.
offset: usize, offset: usize,
/// Max color for slab coloring. /// Max color for slab coloring.
max_color: usize, max_color: u16,
/// Current color for slab coloring. /// Current color for slab coloring.
color: usize, color: u16,
/// Zone lock. /// Zone lock.
lock: ke.Mutex, lock: ke.Mutex,
/// List of full slabs in this zone. /// List of full slabs in this zone.
@@ -372,13 +458,16 @@ pub const Zone = struct {
use_magazines: bool, use_magazines: bool,
reuse_policy: ReusePolicy,
const Self = @This(); const Self = @This();
pub const InitOptions = struct { const InitOptions = struct {
alignment: usize = 0, alignment: u16 = 0,
ctor: ?*const fn (*anyopaque) void = null, ctor: ?*const fn (*anyopaque) void = null,
dtor: ?*const fn (*anyopaque) void = null, dtor: ?*const fn (*anyopaque) void = null,
magazines: bool = true, magazines: bool = true,
reuse_policy: ReusePolicy = .FIFO,
}; };
/// Initialize a zone. /// Initialize a zone.
@@ -402,7 +491,7 @@ pub const Zone = struct {
self.alignment = obj_align; self.alignment = obj_align;
self.slab_size = slab_size; self.slab_size = slab_size;
self.chunk_size = chunk_size; self.chunk_size = chunk_size;
self.max_color = max_color; self.max_color = @intCast(max_color);
self.color = 0; self.color = 0;
self.ctor = options.ctor; self.ctor = options.ctor;
self.dtor = options.dtor; self.dtor = options.dtor;
@@ -415,6 +504,7 @@ pub const Zone = struct {
self.cpu_depot_size = 0; self.cpu_depot_size = 0;
self.cpu_depot_limit = max_local_memory.load() / (self.chunk_size * magazine_size.load()); self.cpu_depot_limit = max_local_memory.load() / (self.chunk_size * magazine_size.load());
self.trim_depot = false; self.trim_depot = false;
self.reuse_policy = options.reuse_policy;
zone_list_lock.acquire(); zone_list_lock.acquire();
@@ -489,7 +579,7 @@ pub const Zone = struct {
if (Depot.alloc(&cpu.depot.full_mags)) |full_mag| { if (Depot.alloc(&cpu.depot.full_mags)) |full_mag| {
// Discard our empty alloc magazine to the depot. // Discard our empty alloc magazine to the depot.
if (cpu.alloc) |empty_mag| { if (cpu.alloc) |empty_mag| {
Depot.free(empty_mag, &cpu.depot.empty_mags); Depot.free(empty_mag, &cpu.depot.empty_mags, self.reuse_policy);
} }
cpu.alloc = full_mag; cpu.alloc = full_mag;
@@ -508,7 +598,7 @@ pub const Zone = struct {
if (Depot.alloc(&cpu.depot.full_mags)) |full_mag| { if (Depot.alloc(&cpu.depot.full_mags)) |full_mag| {
// Discard our empty alloc magazine to the depot. // Discard our empty alloc magazine to the depot.
if (cpu.alloc) |empty_mag| { if (cpu.alloc) |empty_mag| {
Depot.free(empty_mag, &cpu.depot.empty_mags); Depot.free(empty_mag, &cpu.depot.empty_mags, self.reuse_policy);
} }
cpu.alloc = full_mag; cpu.alloc = full_mag;
@@ -609,7 +699,7 @@ pub const Zone = struct {
if (Depot.alloc(&cpu.depot.empty_mags)) |empty_mag| { if (Depot.alloc(&cpu.depot.empty_mags)) |empty_mag| {
// Put the free magazine on the full list. // Put the free magazine on the full list.
if (cpu.free) |full_mag| { if (cpu.free) |full_mag| {
Depot.free(full_mag, &cpu.depot.full_mags); Depot.free(full_mag, &cpu.depot.full_mags, self.reuse_policy);
} }
cpu.free = empty_mag; cpu.free = empty_mag;
@@ -627,7 +717,7 @@ pub const Zone = struct {
if (Depot.alloc(&cpu.depot.empty_mags)) |empty_mag| { if (Depot.alloc(&cpu.depot.empty_mags)) |empty_mag| {
// Put the free magazine on the full list. // Put the free magazine on the full list.
if (cpu.free) |full_mag| { if (cpu.free) |full_mag| {
Depot.free(full_mag, &cpu.depot.full_mags); Depot.free(full_mag, &cpu.depot.full_mags, self.reuse_policy);
} }
cpu.free = empty_mag; cpu.free = empty_mag;
@@ -648,7 +738,7 @@ pub const Zone = struct {
if (new_mag) |m| { if (new_mag) |m| {
// Got one, try again. // Got one, try again.
Depot.free(m, &cpu.depot.empty_mags); Depot.free(m, &cpu.depot.empty_mags, self.reuse_policy);
continue; continue;
} }
@@ -692,7 +782,7 @@ pub const Zone = struct {
// There were no buffers in the slab, so it wasn't in the freelist. // There were no buffers in the slab, so it wasn't in the freelist.
// Now that there is a buffer, add it back to the freelist. // Now that there is a buffer, add it back to the freelist.
slab.link.remove(); slab.link.remove();
self.partial_slabs.insert_head(&slab.link); self.partial_slabs.insert_tail(&slab.link);
} }
if (slab.refcount == 0) { if (slab.refcount == 0) {
@@ -804,11 +894,11 @@ pub const Zone = struct {
var depot = std.mem.zeroes(Depot); var depot = std.mem.zeroes(Depot);
for (0..ke.ncpus) |i| { for (0..ke.ncpus) |i| {
trim_cpu(&self.cpus[i], &depot, self.cpu_depot_size); self.trim_cpu(&self.cpus[i], &depot, self.cpu_depot_size);
} }
self.maglist_destroy(depot.empty_mags.list, 0); self.maglist_destroy(depot.empty_mags.head, 0);
self.maglist_destroy(depot.full_mags.list, magazine_size.load()); self.maglist_destroy(depot.full_mags.head, magazine_size.load());
} }
self.lock.release(); self.lock.release();
@@ -833,11 +923,11 @@ pub const Zone = struct {
// Trim all CPU depots to 0. // Trim all CPU depots to 0.
for (0..ke.ncpus) |i| { for (0..ke.ncpus) |i| {
trim_cpu(&self.cpus[i], &depot, 0); self.trim_cpu(&self.cpus[i], &depot, 0);
} }
self.maglist_destroy(depot.empty_mags.list, 0); self.maglist_destroy(depot.empty_mags.head, 0);
self.maglist_destroy(depot.full_mags.list, magazine_size.load()); self.maglist_destroy(depot.full_mags.head, magazine_size.load());
self.lock.release(); self.lock.release();
} }
@@ -851,14 +941,14 @@ pub const Zone = struct {
maglist.wma, maglist.wma,
) / wma_unit; ) / wma_unit;
var removed_head: ?*Magazine = maglist.list; var removed_head: ?*Magazine = maglist.head;
var last_removed: ?*Magazine = null; var last_removed: ?*Magazine = null;
var removed: usize = 0; var removed: usize = 0;
for (0..target) |_| { for (0..target) |_| {
if (maglist.list) |head| { if (maglist.head) |head| {
last_removed = head; last_removed = head;
maglist.list = head.next; maglist.head = head.next;
removed += 1; removed += 1;
} else break; } else break;
} }
@@ -880,7 +970,7 @@ pub const Zone = struct {
} }
/// Trim a CPU's depot to `target`. /// Trim a CPU's depot to `target`.
fn trim_cpu(cpu: *Cpu, depot: *Depot, target: usize) void { fn trim_cpu(self: *Self, cpu: *Cpu, depot: *Depot, target: usize) void {
const ipl = cpu.lock.acquire(); const ipl = cpu.lock.acquire();
// Split the target (cpu_depot_size) in 2 for each magazine type. // Split the target (cpu_depot_size) in 2 for each magazine type.
@@ -895,7 +985,7 @@ pub const Zone = struct {
// Move them to our depot. // Move them to our depot.
for (0..n) |_| { for (0..n) |_| {
Depot.free(Depot.alloc(&cpu.depot.full_mags).?, &depot.full_mags); Depot.free(Depot.alloc(&cpu.depot.full_mags).?, &depot.full_mags, self.reuse_policy);
} }
} }
@@ -905,7 +995,7 @@ pub const Zone = struct {
// Move them to our depot. // Move them to our depot.
for (0..n) |_| { for (0..n) |_| {
Depot.free(Depot.alloc(&cpu.depot.empty_mags).?, &depot.empty_mags); Depot.free(Depot.alloc(&cpu.depot.empty_mags).?, &depot.empty_mags, self.reuse_policy);
} }
} }
@@ -960,6 +1050,7 @@ pub const Zone = struct {
// Slab info is located at the beginning of the page. // Slab info is located at the beginning of the page.
var slab: *Slab = @ptrCast(@alignCast(buf)); var slab: *Slab = @ptrCast(@alignCast(buf));
slab.alloc_rr = 0;
slab.refcount = 0; slab.refcount = 0;
slab.capacity = @intCast(capacity); slab.capacity = @intCast(capacity);
slab.base = @intFromPtr(slab) + @sizeOf(Slab) + Slab.bitmap_bytes(slab.capacity) + self.color; slab.base = @intFromPtr(slab) + @sizeOf(Slab) + Slab.bitmap_bytes(slab.capacity) + self.color;
@@ -1005,9 +1096,10 @@ pub const Zone = struct {
if (rem > 0) bm[full_words] = (@as(u64, 1) << @intCast(rem)) - 1; if (rem > 0) bm[full_words] = (@as(u64, 1) << @intCast(rem)) - 1;
ret.base = @intFromPtr(buf) + self.color; ret.base = @intFromPtr(buf) + self.color;
ret.buf = @intFromPtr(buf); ret.color = self.color;
ret.capacity = @intCast(capacity); ret.capacity = @intCast(capacity);
ret.refcount = 0; ret.refcount = 0;
ret.alloc_rr = 0;
for (0..self.slab_size / mm.page_size) |i| { for (0..self.slab_size / mm.page_size) |i| {
const phys_page = mi.kernel_space.pmap.query(@intFromPtr(buf) + i * mm.page_size) orelse @panic("Could not query page"); const phys_page = mi.kernel_space.pmap.query(@intFromPtr(buf) + i * mm.page_size) orelse @panic("Could not query page");
@@ -1050,7 +1142,7 @@ pub const Zone = struct {
const alloc_size = @sizeOf(Slab) + Slab.bitmap_bytes(slab.capacity); const alloc_size = @sizeOf(Slab) + Slab.bitmap_bytes(slab.capacity);
gpa.free(@as([*]u8, @ptrCast(slab))[0..alloc_size]); gpa.free(@as([*]u8, @ptrCast(slab))[0..alloc_size]);
mm.heap.free(slab.buf, self.slab_size); mm.heap.free(slab.base - slab.color, self.slab_size);
} else { } else {
free_page(@ptrFromInt(std.mem.alignBackward(usize, @intFromPtr(slab), mm.page_size))); free_page(@ptrFromInt(std.mem.alignBackward(usize, @intFromPtr(slab), mm.page_size)));
} }
@@ -1071,14 +1163,14 @@ pub const Zone = struct {
const n = cpu.depot.empty_mags.num - target / 2; const n = cpu.depot.empty_mags.num - target / 2;
for (0..n) |_| { for (0..n) |_| {
Depot.free(Depot.alloc(&cpu.depot.empty_mags).?, &self.depot.empty_mags); Depot.free(Depot.alloc(&cpu.depot.empty_mags).?, &self.depot.empty_mags, self.reuse_policy);
} }
} }
// Grab a batch of full magazines from the zone depot. // Grab a batch of full magazines from the zone depot.
const n = @min(target - cpu.depot.empty_mags.num, self.depot.full_mags.num); const n = @min(target - cpu.depot.empty_mags.num, self.depot.full_mags.num);
for (0..n) |_| { for (0..n) |_| {
Depot.free(Depot.alloc(&self.depot.full_mags).?, &cpu.depot.full_mags); Depot.free(Depot.alloc(&self.depot.full_mags).?, &cpu.depot.full_mags, self.reuse_policy);
} }
self.depot_lock.release_no_ipl(); self.depot_lock.release_no_ipl();
@@ -1099,14 +1191,14 @@ pub const Zone = struct {
const n = cpu.depot.full_mags.num - target / 2; const n = cpu.depot.full_mags.num - target / 2;
for (0..n) |_| { for (0..n) |_| {
Depot.free(Depot.alloc(&cpu.depot.full_mags).?, &self.depot.full_mags); Depot.free(Depot.alloc(&cpu.depot.full_mags).?, &self.depot.full_mags, self.reuse_policy);
} }
} }
// Grab a batch of empty magazines from the zone depot. // Grab a batch of empty magazines from the zone depot.
const n = @min(target - cpu.depot.full_mags.num, self.depot.empty_mags.num); const n = @min(target - cpu.depot.full_mags.num, self.depot.empty_mags.num);
for (0..n) |_| { for (0..n) |_| {
Depot.free(Depot.alloc(&self.depot.empty_mags).?, &cpu.depot.empty_mags); Depot.free(Depot.alloc(&self.depot.empty_mags).?, &cpu.depot.empty_mags, self.reuse_policy);
} }
self.depot_lock.release_no_ipl(); self.depot_lock.release_no_ipl();