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std.Progress: fix race condition with IPC nodes
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It stored some metadata into the canonical node storage data but that is
a race condition because another thread recycles those nodes.

Also, keep the parent name for empty child root node names.
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@andrewrk
andrewrk committed May 24, 2024
1 parent da2a9c1 commit a0c6e72
Showing 1 changed file with 49 additions and 40 deletions.
89 changes: 49 additions & 40 deletions lib/std/Progress.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -86,17 +86,7 @@ pub const Node = struct {
name: [max_name_len]u8,

fn getIpcFd(s: Storage) ?posix.fd_t {
if (s.estimated_total_count != std.math.maxInt(u32))
return null;

const low: u16 = @truncate(s.completed_count);
return low;
}

fn getMainStorageIndex(s: Storage) Node.Index {
assert(s.estimated_total_count == std.math.maxInt(u32));
const i: u16 = @truncate(s.completed_count >> 16);
return @enumFromInt(i);
return if (s.estimated_total_count != std.math.maxInt(u32)) null else @bitCast(s.completed_count);
}

fn setIpcFd(s: *Storage, fd: posix.fd_t) void {
Expand Down Expand Up @@ -538,14 +528,9 @@ fn serialize() Serialized {
@memcpy(&dest_storage.name, &storage_ptr.name);
dest_storage.completed_count = @atomicLoad(u32, &storage_ptr.completed_count, .monotonic);
dest_storage.estimated_total_count = @atomicLoad(u32, &storage_ptr.estimated_total_count, .monotonic);

if (dest_storage.getIpcFd() != null) {
any_ipc = true;
dest_storage.completed_count |= @as(u32, @intCast(i)) << 16;
}

const end_parent = @atomicLoad(Node.Parent, parent_ptr, .seq_cst);
if (begin_parent == end_parent) {
any_ipc = any_ipc or (dest_storage.getIpcFd() != null);
serialized_node_parents_buffer[serialized_len] = begin_parent;
serialized_node_map_buffer[i] = @enumFromInt(serialized_len);
serialized_len += 1;
Expand Down Expand Up @@ -577,23 +562,25 @@ fn serialize() Serialized {

var parents_copy: [default_node_storage_buffer_len]Node.Parent = undefined;
var storage_copy: [default_node_storage_buffer_len]Node.Storage = undefined;
var ipc_metadata_copy: [default_node_storage_buffer_len]SavedMetadata = undefined;

const SavedMetadata = extern struct {
var ipc_metadata: [default_node_storage_buffer_len]SavedMetadata = undefined;
var ipc_metadata_len: u16 = 0;

const SavedMetadata = struct {
ipc_fd: u16,
main_index: u16,
start_index: u16,
nodes_len: u16,
main_index: u16,
flags: Flags,

const Flags = enum(u16) {
saved = std.math.maxInt(u16),
_,
};
};

fn serializeIpc(start_serialized_len: usize) usize {
var serialized_len = start_serialized_len;
var pipe_buf: [2 * 4096]u8 align(4) = undefined;

const old_ipc_metadata = ipc_metadata_copy[0..ipc_metadata_len];
ipc_metadata_len = 0;

main_loop: for (
serialized_node_parents_buffer[0..serialized_len],
serialized_node_storage_buffer[0..serialized_len],
Expand All @@ -618,23 +605,23 @@ fn serializeIpc(start_serialized_len: usize) usize {
// Ignore all but the last message on the pipe.
var input: []align(2) u8 = pipe_buf[0..bytes_read];
if (input.len == 0) {
serialized_len = useSavedIpcData(serialized_len, main_storage, main_index);
serialized_len = useSavedIpcData(serialized_len, main_storage, main_index, old_ipc_metadata);
continue;
}

const storage, const parents = while (true) {
if (input.len < 4) {
std.log.warn("short read: {d} out of 4 header bytes", .{input.len});
// TODO keep track of the short read to trash odd bytes with the next read
serialized_len = useSavedIpcData(serialized_len, main_storage, main_index);
serialized_len = useSavedIpcData(serialized_len, main_storage, main_index, old_ipc_metadata);
continue :main_loop;
}
const subtree_len = std.mem.readInt(u32, input[0..4], .little);
const expected_bytes = 4 + subtree_len * (@sizeOf(Node.Storage) + @sizeOf(Node.Parent));
if (input.len < expected_bytes) {
std.log.warn("short read: {d} out of {d} ({d} nodes)", .{ input.len, expected_bytes, subtree_len });
// TODO keep track of the short read to trash odd bytes with the next read
serialized_len = useSavedIpcData(serialized_len, main_storage, main_index);
serialized_len = useSavedIpcData(serialized_len, main_storage, main_index, old_ipc_metadata);
continue :main_loop;
}
if (input.len > expected_bytes) {
Expand All @@ -650,16 +637,16 @@ fn serializeIpc(start_serialized_len: usize) usize {
};

// Remember in case the pipe is empty on next update.
const real_storage: *Node.Storage = Node.storageByIndex(main_storage.getMainStorageIndex());
@as(*SavedMetadata, @ptrCast(&real_storage.name)).* = .{
ipc_metadata[ipc_metadata_len] = .{
.ipc_fd = @intCast(fd),
.start_index = @intCast(serialized_len),
.nodes_len = @intCast(parents.len),
.main_index = @intCast(main_index),
.flags = .saved,
};
ipc_metadata_len += 1;

// Mount the root here.
main_storage.* = storage[0];
copyRoot(main_storage, &storage[0]);

// Copy the rest of the tree to the end.
@memcpy(serialized_node_storage_buffer[serialized_len..][0 .. storage.len - 1], storage[1..]);
Expand All @@ -685,34 +672,56 @@ fn serializeIpc(start_serialized_len: usize) usize {
// Save a copy in case any pipes are empty on the next update.
@memcpy(parents_copy[0..serialized_len], serialized_node_parents_buffer[0..serialized_len]);
@memcpy(storage_copy[0..serialized_len], serialized_node_storage_buffer[0..serialized_len]);
@memcpy(ipc_metadata_copy[0..ipc_metadata_len], ipc_metadata[0..ipc_metadata_len]);

return serialized_len;
}

fn useSavedIpcData(start_serialized_len: usize, main_storage: *Node.Storage, main_index: usize) usize {
const saved_metadata: *SavedMetadata = @ptrCast(&main_storage.name);
if (saved_metadata.flags != .saved) {
fn copyRoot(dest: *Node.Storage, src: *align(2) Node.Storage) void {
dest.* = .{
.completed_count = src.completed_count,
.estimated_total_count = src.estimated_total_count,
.name = if (src.name[0] == 0) dest.name else src.name,
};
}

fn findOld(ipc_fd: posix.fd_t, old_metadata: []const SavedMetadata) ?*const SavedMetadata {
for (old_metadata) |*m| {
if (m.ipc_fd == ipc_fd)
return m;
}
return null;
}

fn useSavedIpcData(
start_serialized_len: usize,
main_storage: *Node.Storage,
main_index: usize,
old_metadata: []const SavedMetadata,
) usize {
const ipc_fd = main_storage.getIpcFd().?;
const saved_metadata = findOld(ipc_fd, old_metadata) orelse {
main_storage.completed_count = 0;
main_storage.estimated_total_count = 0;
return start_serialized_len;
}
};

const start_index = saved_metadata.start_index;
const nodes_len = saved_metadata.nodes_len;
const old_main_index = saved_metadata.main_index;

const real_storage: *Node.Storage = Node.storageByIndex(main_storage.getMainStorageIndex());
@as(*SavedMetadata, @ptrCast(&real_storage.name)).* = .{
ipc_metadata[ipc_metadata_len] = .{
.ipc_fd = @intCast(ipc_fd),
.start_index = @intCast(start_serialized_len),
.nodes_len = nodes_len,
.main_index = @intCast(main_index),
.flags = .saved,
};
ipc_metadata_len += 1;

const parents = parents_copy[start_index..][0 .. nodes_len - 1];
const storage = storage_copy[start_index..][0 .. nodes_len - 1];

main_storage.* = storage_copy[old_main_index];
copyRoot(main_storage, &storage_copy[old_main_index]);

@memcpy(serialized_node_storage_buffer[start_serialized_len..][0..storage.len], storage);

Expand Down

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