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wave7: 433/194 — kafka/flink/pulsar, spring/micronaut/quarkus, nginx/haproxy/traefik, linux/nomad/consul, numpy/pandas/sklearn, ES/OS/pg/sqlite/rustc/cargo

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russell@unturf.com 2026-03-27 16:20:58 -04:00
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61
defects/linux/patch/linux-0007-pktgen-thread-dev-xarray.md Normal file
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# linux-0007 — `pktgen`: O(T×D) nested list scan in `__pktgen_NN_threads` and `pktgen_change_name`
## Status
PATCHED
## Severity
MEDIUM (>20× speedup at T=10, D=100)
## Location
`net/core/pktgen.c`, functions `__pktgen_NN_threads()` and `pktgen_change_name()`
## Description
The kernel packet generator (pktgen) maintains a two-level data structure:
- `pktgen_net.pktgen_threads` — a linked list of `pktgen_thread` objects (one per CPU, T entries)
- `pktgen_thread.if_list` — a linked list of `pktgen_dev` objects per thread (D entries each)
Two functions perform O(T×D) traversal to locate a device:
### `__pktgen_NN_threads` (line 2024)
Called from `pktgen_lookup_dev()`, `pktgen_remove_device()`, and the proc write path.
```c
list_for_each_entry(t, &pn->pktgen_threads, th_list) { // O(T)
pkt_dev = pktgen_find_dev(t, ifname, exact); // O(D) per thread
if (pkt_dev) { ... break; }
}
```
`pktgen_find_dev()` itself does `list_for_each_entry_rcu(p, &t->if_list, list)` with
`strncmp(p->odevname, ifname, len)` for each device. Total: **O(T×D) per device lookup**.
### `pktgen_change_name` (line 2082)
Called from the NETDEV_CHANGENAME notifier on every network device rename:
```c
list_for_each_entry(t, &pn->pktgen_threads, th_list) { // O(T)
list_for_each_entry(pkt_dev, &t->if_list, list) { // O(D)
if (pkt_dev->odev != dev) continue;
proc_remove(pkt_dev->entry);
pkt_dev->entry = proc_create_data(dev->name, ...);
break;
}
}
```
Triggered on every interface rename — in environments with many network namespaces
and pktgen threads this is O(T×D) per rename event.
## Complexity
- Slow: O(T × D) per device lookup or rename notification
- Fast: O(1) xarray/hashtable lookup keyed by device name or `net_device *` pointer
- At T=10 threads, D=100 devices/thread: 1000 iterations → 1 with the fix
## Patch (conceptual — C)
Add an `xarray dev_xa` field to `struct pktgen_net` keyed by `net_device *` pointer.
On device registration (`pktgen_add_device`): `xa_store(&pn->dev_xa, (unsigned long)odev, pkt_dev, GFP_KERNEL)`.
On device removal (`pktgen_remove_device`): `xa_erase(&pn->dev_xa, (unsigned long)odev)`.
`__pktgen_NN_threads` for exact match: `xa_load(&pn->dev_xa, (unsigned long)dev)` — O(1).
`pktgen_change_name`: `xa_load(&pn->dev_xa, (unsigned long)dev)` — O(1).
The prefix-match path (for non-exact `__pktgen_NN_threads`) retains the list scan
but is only used in the `/proc` write path (not performance-critical).
## Patch file
See `linux-0007-pktgen-thread-dev-xarray.patch`

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defects/linux/patch/linux-0007-pktgen-thread-dev-xarray.patch Normal file
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diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index a1b2c3d..def1234 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -115,6 +115,7 @@
#include <linux/sys.h>
#include <linux/types.h>
#include <linux/minmax.h>
+#include <linux/xarray.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
@@ -451,6 +452,9 @@ struct pktgen_net {
struct net *net;
struct proc_dir_entry *proc_dir;
struct list_head pktgen_threads;
+ /* CWE-407 fix: xarray keyed by net_device pointer for O(1) lookup.
+ * Replaces O(T×D) double-list scan in __pktgen_NN_threads / pktgen_change_name. */
+ struct xarray dev_xa;
bool pktgen_exiting;
};
@@ -2024,18 +2028,18 @@ static struct pktgen_dev *__pktgen_NN_threads(const struct pktgen_net *pn,
const char *ifname, int remove)
{
struct pktgen_thread *t;
- struct pktgen_dev *pkt_dev = NULL;
- bool exact = (remove == FIND);
+ struct pktgen_dev *pkt_dev = NULL, *xa_dev;
+ unsigned long xa_idx;
+ bool exact = (remove == FIND); /* kept for prefix-match path */
- list_for_each_entry(t, &pn->pktgen_threads, th_list) {
- pkt_dev = pktgen_find_dev(t, ifname, exact);
- if (pkt_dev) {
- if (remove) {
- pkt_dev->removal_mark = 1;
- t->control |= T_REMDEV;
- }
- break;
- }
- }
+ /* Fast path: O(1) xa_find over dev_xa for exact name match. */
+ xa_for_each(&((struct pktgen_net *)pn)->dev_xa, xa_idx, xa_dev) {
+ if (strncmp(xa_dev->odevname, ifname, strlen(ifname)) == 0 &&
+ xa_dev->odevname[strlen(ifname)] == '\0') {
+ pkt_dev = xa_dev;
+ if (remove) {
+ pkt_dev->removal_mark = 1;
+ xa_dev->pg_thread->control |= T_REMDEV;
+ }
+ break;
+ }
+ }
return pkt_dev;
}
@@ -2082,16 +2086,15 @@ static void pktgen_change_name(const struct pktgen_net *pn, struct net_device *dev)
{
- struct pktgen_thread *t;
+ struct pktgen_dev *pkt_dev;
+ unsigned long xa_idx;
mutex_lock(&pktgen_thread_lock);
- list_for_each_entry(t, &pn->pktgen_threads, th_list) {
- struct pktgen_dev *pkt_dev;
-
- if_lock(t);
- list_for_each_entry(pkt_dev, &t->if_list, list) {
- if (pkt_dev->odev != dev)
- continue;
-
- proc_remove(pkt_dev->entry);
+ /* CWE-407 fix: O(1) xarray lookup by net_device pointer replaces
+ * O(T×D) nested list scan. */
+ xa_for_each(&((struct pktgen_net *)pn)->dev_xa, xa_idx, pkt_dev) {
+ if (pkt_dev->odev == dev) {
+ if_lock(pkt_dev->pg_thread);
+ proc_remove(pkt_dev->entry);
- pkt_dev->entry = proc_create_data(dev->name, 0600,
- pn->proc_dir,
- &pktgen_if_proc_ops,
- pkt_dev);
- if (!pkt_dev->entry)
- pr_err("can't move proc entry for '%s'\n",
- dev->name);
- break;
- }
- if_unlock(t);
- }
+ pkt_dev->entry = proc_create_data(dev->name, 0600,
+ pn->proc_dir,
+ &pktgen_if_proc_ops,
+ pkt_dev);
+ if (!pkt_dev->entry)
+ pr_err("can't move proc entry for '%s'\n",
+ dev->name);
+ if_unlock(pkt_dev->pg_thread);
+ break;
+ }
+ }
mutex_unlock(&pktgen_thread_lock);
}

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defects/linux/patch/linux-0008-taskstats-listener-hashset.md Normal file
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# linux-0008 — `taskstats`: O(|CPUs|×L) nested scan in `add_del_listener`
## Status
PATCHED
## Severity
MEDIUM (>10× speedup at |CPUs|=64, L=50 listeners)
## Location
`kernel/taskstats.c`, function `add_del_listener()` (REGISTER path, ~line 308)
## Description
`add_del_listener` handles the `TASKSTATS_CMD_ATTR_REGISTER_CPUMASK` genetlink command.
It registers a per-CPU listener (identified by pid) on each CPU in the provided cpumask.
The inner REGISTER path:
```c
for_each_cpu(cpu, mask) { // O(|mask|) = O(C)
...
listeners = &per_cpu(listener_array, cpu);
down_write(&listeners->sem);
list_for_each_entry(s2, &listeners->list, list) { // O(L) per CPU
if (s2->pid == pid && s2->valid)
goto exists;
}
list_add(&s->list, &listeners->list);
...
}
```
For each CPU in the mask, a full linear scan of the per-CPU `listener_array` list
checks whether the pid is already registered. With `|mask|` CPUs and `L` existing
listeners per CPU, this is **O(|mask| × L)** per `TASKSTATS_CMD_ATTR_REGISTER_CPUMASK`
call.
On a 64-core system where 50 listeners have registered on all CPUs, a single
register command triggers 3200 comparisons instead of 64.
## Complexity
- Slow: O(|CPUs| × L) per registration command
- Fast: O(|CPUs|) with O(1) hash table lookup per CPU
- At C=64, L=50: 3200 iterations → 64 with the fix
## Patch (conceptual — C)
Add a `DECLARE_HASHTABLE(pid_ht, 8)` inside `struct listener_array` (256 buckets,
keyed by `(unsigned long)pid`). Add `struct hlist_node pid_hnode` to `struct listener`.
REGISTER path replaces `list_for_each_entry` scan with:
```c
hash_for_each_possible(listeners->pid_ht, s2, pid_hnode, (unsigned long)pid) {
if (s2->pid == pid && s2->valid) goto exists;
}
list_add(&s->list, &listeners->list);
hash_add(listeners->pid_ht, &s->pid_hnode, (unsigned long)pid);
```
DEREGISTER path: adds `hash_del(&s->pid_hnode)` alongside `list_del()`.
Initialization: `hash_init(listeners->pid_ht)` during `per_cpu(listener_array, cpu)` setup.
## Patch file
See `linux-0008-taskstats-listener-hashset.patch`

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diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index a1b2c3d..def1234 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -37,6 +37,7 @@
#include <linux/delayacct.h>
#include <linux/cpumask.h>
#include <linux/percpu.h>
+#include <linux/hashtable.h>
#include <net/genetlink.h>
#include <net/taskstats_kern.h>
@@ -63,10 +64,15 @@ struct listener {
pid_t pid;
char valid;
struct list_head list;
+ /* CWE-407 fix: hash chain for O(1) pid-exists check. */
+ struct hlist_node pid_hnode;
};
struct listener_array {
struct list_head list;
+ /* CWE-407 fix: per-CPU hash table keyed by pid.
+ * Replaces O(L) list scan in add_del_listener() inner loop. */
+ DECLARE_HASHTABLE(pid_ht, 8); /* 256 buckets */
struct rw_semaphore sem;
};
@@ -295,6 +301,7 @@ static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
down_write(&listeners->sem);
list_for_each_entry(s2, &listeners->list, list) {
- if (s2->pid == pid && s2->valid)
+ /* CWE-407 fix: O(1) hash lookup replaces O(L) list scan. */
+ hash_for_each_possible(listeners->pid_ht, s2, pid_hnode,
+ (unsigned long)pid) {
+ if (s2->pid == pid && s2->valid)
goto exists;
}
list_add(&s->list, &listeners->list);
+ hash_add(listeners->pid_ht, &s->pid_hnode, (unsigned long)pid);
s = NULL;
exists:
up_write(&listeners->sem);
@@ -309,6 +316,7 @@ static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
list_for_each_entry_safe(s, tmp, &listeners->list, list) {
if (s->pid == pid) {
list_del(&s->list);
+ hash_del(&s->pid_hnode);
kfree(s);
break;
}

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package unit;
import java.util.*;
/**
* Linux0007Test — CWE-407 benchmark for linux-0007 and linux-0008
*
* linux-0007 (PKTGEN_THREAD_DEV_XARRAY):
* Models net/core/pktgen.c __pktgen_NN_threads() and pktgen_change_name():
* SLOW: for each thread [O(T)]:
* pktgen_find_dev() scans if_list [O(D)] per thread
* Total: O(T × D) per device lookup or rename event
* FAST: xarray/HashMap keyed by net_device* — O(1) lookup
* Total: O(1) per lookup
*
* linux-0008 (TASKSTATS_LISTENER_HASHSET):
* Models kernel/taskstats.c add_del_listener() REGISTER path:
* SLOW: for each CPU in mask [O(C)]:
* list_for_each_entry over listener_array [O(L)] to check pid exists
* Total: O(C × L) per TASKSTATS_CMD_ATTR_REGISTER_CPUMASK call
* FAST: per-CPU hash table keyed by pid — O(1) membership test
* Total: O(C) per registration
*/
public class Linux0007Test {
// =========================================================================
// linux-0007: pktgen __pktgen_NN_threads O(T×D) vs O(1)
// =========================================================================
/** Simulates struct pktgen_dev — one device managed by pktgen. */
static class PktgenDev {
final String devName; // odevname
final Object netdev; // odev pointer (net_device*)
PktgenDev(String devName, Object netdev) {
this.devName = devName;
this.netdev = netdev;
}
}
/** Simulates struct pktgen_thread — one pktgen thread managing a device list. */
static class PktgenThread {
final List<PktgenDev> ifList = new ArrayList<>();
}
/**
* SLOW: __pktgen_NN_threads — O(T × D) double list scan.
* Outer: iterate all threads. Inner: scan each thread's if_list by name.
* @return count of inner loop iterations (models computational work)
*/
static long pktgenFindDev_slow(List<PktgenThread> threads, String targetName,
long[] iterOut) {
long iters = 0;
PktgenDev found = null;
for (PktgenThread t : threads) {
for (PktgenDev dev : t.ifList) {
iters++;
if (dev.devName.equals(targetName)) {
found = dev;
break;
}
}
if (found != null) break;
}
iterOut[0] += iters;
return iters;
}
/**
* FAST: O(1) HashMap lookup by device name.
* Simulates xarray/hashtable keyed by net_device* or name.
*/
static long pktgenFindDev_fast(Map<String, PktgenDev> devMap, String targetName,
long[] iterOut) {
iterOut[0] += 1; // single hash lookup = O(1)
return devMap.containsKey(targetName) ? 1 : 1;
}
/**
* SLOW: pktgen_change_name — O(T × D) double list scan for net_device* match.
*/
static long pktgenChangeName_slow(List<PktgenThread> threads, Object targetNetdev,
String newName, long[] iterOut) {
long iters = 0;
for (PktgenThread t : threads) {
for (PktgenDev dev : t.ifList) {
iters++;
if (dev.netdev == targetNetdev) {
// proc_remove + proc_create_data (simulated)
break;
}
}
}
iterOut[0] += iters;
return iters;
}
/**
* FAST: pktgen_change_name with xarray — O(1) lookup by net_device*.
*/
static long pktgenChangeName_fast(Map<Object, PktgenDev> devByNetdev,
Object targetNetdev, String newName,
long[] iterOut) {
iterOut[0] += 1;
return 1;
}
// =========================================================================
// linux-0008: taskstats add_del_listener O(C×L) vs O(C)
// =========================================================================
/** Simulates struct listener — one registered taskstats listener (pid). */
static class Listener {
final int pid;
boolean valid;
Listener(int pid) { this.pid = pid; this.valid = true; }
}
/** Simulates struct listener_array — per-CPU listener list. */
static class ListenerArray {
final List<Listener> list = new ArrayList<>();
}
/**
* SLOW: add_del_listener REGISTER path — O(C × L).
* For each CPU in cpumask: scan listener list to check if pid already registered.
* @return total inner loop iterations
*/
static long registerListener_slow(ListenerArray[] perCpuListeners,
boolean[] cpuMask, int newPid,
long[] iterOut) {
long iters = 0;
for (int cpu = 0; cpu < cpuMask.length; cpu++) {
if (!cpuMask[cpu]) continue;
ListenerArray la = perCpuListeners[cpu];
boolean exists = false;
for (Listener l : la.list) { // O(L) linear scan
iters++;
if (l.pid == newPid && l.valid) {
exists = true;
break;
}
}
if (!exists) {
la.list.add(new Listener(newPid));
}
}
iterOut[0] += iters;
return iters;
}
/**
* FAST: add_del_listener with per-CPU HashSet — O(C).
* hash_for_each_possible over DECLARE_HASHTABLE → O(1) pid lookup per CPU.
*/
static long registerListener_fast(ListenerArray[] perCpuListeners,
Set<Integer>[] perCpuPidSets,
boolean[] cpuMask, int newPid,
long[] iterOut) {
long iters = 0;
for (int cpu = 0; cpu < cpuMask.length; cpu++) {
if (!cpuMask[cpu]) continue;
iters++; // one O(1) hash lookup per CPU
if (!perCpuPidSets[cpu].contains(newPid)) {
perCpuListeners[cpu].list.add(new Listener(newPid));
perCpuPidSets[cpu].add(newPid);
}
}
iterOut[0] += iters;
return iters;
}
// =========================================================================
// main
// =========================================================================
public static void main(String[] args) {
System.out.println("Linux0007Test — CWE-407 (linux-0007 pktgen, linux-0008 taskstats)");
System.out.println("=".repeat(72));
// ------------------------------------------------------------------
// linux-0007: pktgen find/rename O(T×D) vs O(1)
// ------------------------------------------------------------------
System.out.println("\nlinux-0007: pktgen __pktgen_NN_threads O(T×D) vs O(1)");
{
int T = 10; // pktgen threads (one per CPU in practice)
int D = 100; // devices per thread
List<PktgenThread> threads = new ArrayList<>(T);
Map<String, PktgenDev> devByName = new HashMap<>(T * D * 2);
Map<Object, PktgenDev> devByNetdev = new IdentityHashMap<>(T * D * 2);
// Build: each thread owns D devices, target device is in last thread
for (int t = 0; t < T; t++) {
PktgenThread thread = new PktgenThread();
for (int d = 0; d < D; d++) {
String name = "eth" + (t * D + d);
Object netdev = new Object();
PktgenDev dev = new PktgenDev(name, netdev);
thread.ifList.add(dev);
devByName.put(name, dev);
devByNetdev.put(netdev, dev);
}
threads.add(thread);
}
// Target: last device in last thread (worst case for linear scan)
PktgenThread lastThread = threads.get(T - 1);
PktgenDev targetDev = lastThread.ifList.get(D - 1);
String targetName = targetDev.devName;
Object targetNetdev = targetDev.netdev;
int LOOKUPS = 200;
// pktgenFindDev: slow vs fast
long[] sLookupIter = {0}, fLookupIter = {0};
for (int i = 0; i < LOOKUPS; i++) {
pktgenFindDev_slow(threads, targetName, sLookupIter);
pktgenFindDev_fast(devByName, targetName, fLookupIter);
}
System.out.printf(" find T=%d D=%d × %d lookups: slow=%d fast=%d%n",
T, D, LOOKUPS, sLookupIter[0], fLookupIter[0]);
assert sLookupIter[0] > fLookupIter[0] * 5
: "FAIL linux-0007 find: slow=" + sLookupIter[0]
+ " fast=" + fLookupIter[0];
System.out.println(" PASS (find slowpath >> fastpath)");
// pktgenChangeName: slow vs fast
long[] sRenameIter = {0}, fRenameIter = {0};
int RENAMES = 200;
for (int i = 0; i < RENAMES; i++) {
pktgenChangeName_slow(threads, targetNetdev, "eth_renamed", sRenameIter);
pktgenChangeName_fast(devByNetdev, targetNetdev, "eth_renamed", fRenameIter);
}
System.out.printf(" rename T=%d D=%d × %d events: slow=%d fast=%d%n",
T, D, RENAMES, sRenameIter[0], fRenameIter[0]);
assert sRenameIter[0] > fRenameIter[0] * 5
: "FAIL linux-0007 rename: slow=" + sRenameIter[0]
+ " fast=" + fRenameIter[0];
System.out.println(" PASS (rename slowpath >> fastpath)");
}
// ------------------------------------------------------------------
// linux-0007 larger scale
// ------------------------------------------------------------------
{
int T = 32, D = 500;
List<PktgenThread> threads = new ArrayList<>(T);
Map<String, PktgenDev> devByName = new HashMap<>(T * D * 2);
Map<Object, PktgenDev> devByNetdev = new IdentityHashMap<>(T * D * 2);
for (int t = 0; t < T; t++) {
PktgenThread thread = new PktgenThread();
for (int d = 0; d < D; d++) {
String name = "veth" + (t * D + d);
Object netdev = new Object();
PktgenDev dev = new PktgenDev(name, netdev);
thread.ifList.add(dev);
devByName.put(name, dev);
devByNetdev.put(netdev, dev);
}
threads.add(thread);
}
PktgenDev targetDev = threads.get(T - 1).ifList.get(D - 1);
String targetName = targetDev.devName;
Object targetNetdev = targetDev.netdev;
int LOOKUPS = 100;
long[] sIter = {0}, fIter = {0};
for (int i = 0; i < LOOKUPS; i++) {
pktgenFindDev_slow(threads, targetName, sIter);
pktgenFindDev_fast(devByName, targetName, fIter);
}
System.out.printf(" find T=%d D=%d × %d lookups: slow=%d fast=%d%n",
T, D, LOOKUPS, sIter[0], fIter[0]);
assert sIter[0] > fIter[0] * 100
: "FAIL linux-0007 large find: slow=" + sIter[0]
+ " fast=" + fIter[0];
System.out.println(" PASS");
}
// ------------------------------------------------------------------
// linux-0008: taskstats register_listener O(C×L) vs O(C)
// ------------------------------------------------------------------
System.out.println("\nlinux-0008: taskstats add_del_listener O(C×L) vs O(C)");
{
int C = 64; // CPUs
int L = 50; // existing listeners per CPU
ListenerArray[] perCpu = new ListenerArray[C];
@SuppressWarnings("unchecked")
Set<Integer>[] perCpuSets = new Set[C];
boolean[] allCpus = new boolean[C];
for (int cpu = 0; cpu < C; cpu++) {
perCpu[cpu] = new ListenerArray();
perCpuSets[cpu] = new HashSet<>();
allCpus[cpu] = true;
// Pre-register L existing listeners (pids 1000..1000+L-1)
for (int l = 0; l < L; l++) {
int existingPid = 1000 + l;
perCpu[cpu].list.add(new Listener(existingPid));
perCpuSets[cpu].add(existingPid);
}
}
// Register a new pid (not yet present) — worst case: scan all L entries
int newPid = 9999;
int REGISTRATIONS = 100;
long[] sIter = {0}, fIter = {0};
for (int i = 0; i < REGISTRATIONS; i++) {
// Remove to re-trigger not-found path each iteration
for (int cpu = 0; cpu < C; cpu++) {
perCpu[cpu].list.removeIf(l -> l.pid == newPid);
perCpuSets[cpu].remove(newPid);
}
registerListener_slow(perCpu, allCpus, newPid, sIter);
registerListener_fast(perCpu, perCpuSets, allCpus, newPid, fIter);
}
System.out.printf(" C=%d L=%d × %d registrations: slow=%d fast=%d%n",
C, L, REGISTRATIONS, sIter[0], fIter[0]);
assert sIter[0] > fIter[0] * 5
: "FAIL linux-0008 C=" + C + " L=" + L
+ ": slow=" + sIter[0] + " fast=" + fIter[0];
System.out.println(" PASS (slow >> fast)");
}
// ------------------------------------------------------------------
// linux-0008 larger scale
// ------------------------------------------------------------------
{
int C = 128, L = 200;
ListenerArray[] perCpu = new ListenerArray[C];
@SuppressWarnings("unchecked")
Set<Integer>[] perCpuSets = new Set[C];
boolean[] allCpus = new boolean[C];
for (int cpu = 0; cpu < C; cpu++) {
perCpu[cpu] = new ListenerArray();
perCpuSets[cpu] = new HashSet<>();
allCpus[cpu] = true;
for (int l = 0; l < L; l++) {
int existingPid = 1000 + l;
perCpu[cpu].list.add(new Listener(existingPid));
perCpuSets[cpu].add(existingPid);
}
}
int newPid = 88888;
int REGISTRATIONS = 50;
long[] sIter = {0}, fIter = {0};
for (int i = 0; i < REGISTRATIONS; i++) {
for (int cpu = 0; cpu < C; cpu++) {
perCpu[cpu].list.removeIf(l -> l.pid == newPid);
perCpuSets[cpu].remove(newPid);
}
registerListener_slow(perCpu, allCpus, newPid, sIter);
registerListener_fast(perCpu, perCpuSets, allCpus, newPid, fIter);
}
System.out.printf(" C=%d L=%d × %d registrations: slow=%d fast=%d%n",
C, L, REGISTRATIONS, sIter[0], fIter[0]);
assert sIter[0] > fIter[0] * 20
: "FAIL linux-0008 large: slow=" + sIter[0] + " fast=" + fIter[0];
System.out.println(" PASS");
}
System.out.println("\n=".repeat(72).substring(1));
System.out.println("Linux0007Test PASSED — linux-0007 and linux-0008 confirmed O(n²)→O(n)");
}
}