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workqueue: debug possible lockups in flush_workqueue

PATCH In review Jarek Poplawski 2 participants 3 messages Apr 19, 2007 Workqueue

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Jarek Poplawski

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#0 lore raw

PATCH 1/1 workqueue: debug possible lockups in flush_workqueue

Hi,

Here is my patch proposal for detecting possible lockups, when flush_workqueue caller holds a lock (e.g. rtnl_lock) also used in work functions.

Regards,
Jarek P.

Signed-off-by Jarek Poplawski <[email protected]>

---

kernel/workqueue.c +21 -0
diff -Nurp 2.6.21-rc6-mm1-/kernel/workqueue.c 2.6.21-rc6-mm1/kernel/workqueue.c
@@ -67,6 +67,12 @@ struct workqueue_struct {
 /* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
    threads to each one as cpus come/go. */
 static DEFINE_MUTEX(workqueue_mutex);
+
+#ifdef CONFIG_PROVE_LOCKING
+/* Detect possible flush_workqueue() lockup with circular dependency check. */
+static struct lockdep_map flush_dep_map = { .name = "flush_dep_map" };
+#endif
+
 static LIST_HEAD(workqueues);
 
 static int singlethread_cpu __read_mostly;

@@ -247,8 +253,15 @@ static void run_workqueue(struct cpu_wor
 
 		BUG_ON(get_wq_data(work) != cwq);
 		work_clear_pending(work);
+#ifdef CONFIG_PROVE_LOCKING
+		/* lockdep dependency: flush_dep_map (read) before any lock: */
+		lock_acquire(&flush_dep_map, 0, 0, 1, 2, _THIS_IP_);
+#endif
 		f(work);
 
+#ifdef CONFIG_PROVE_LOCKING
+		lock_release(&flush_dep_map, 1, _THIS_IP_);
+#endif
 		if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
 			printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
 					"%s/0x%08x/%d\n",

@@ -389,6 +402,14 @@ void fastcall flush_workqueue(struct wor
 	int cpu;
 
 	might_sleep();
+#ifdef CONFIG_PROVE_LOCKING
+	/*
+	 * Add lockdep dependency: flush_dep_map (exclusive)
+	 * after any held mutex or rwsem.
+	 */
+	lock_acquire(&flush_dep_map, 0, 0, 0, 2, _THIS_IP_);
+	lock_release(&flush_dep_map, 1, _THIS_IP_);
+#endif
 	for_each_cpu_mask(cpu, *cpu_map)
 		flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
 }
#1 lore raw
Quoted 3 lines · Jarek Poplawski

Here is my patch proposal for detecting possible lockups, when flush_workqueue caller holds a lock (e.g. rtnl_lock) also used in work functions.

looks good in principle - did you test it and it caught a bug that wasnt caught before?

kernel/workqueue.c struct workqueue_struct {

Quoted 9 lines
kernel/workqueue.c +8 -0
+#ifdef CONFIG_PROVE_LOCKING
+/* Detect possible flush_workqueue() lockup with circular dependency check. */
+static struct lockdep_map flush_dep_map = { .name = "flush_dep_map" };
+#endif
 
+#ifdef CONFIG_PROVE_LOCKING
+		/* lockdep dependency: flush_dep_map (read) before any lock: */
+		lock_acquire(&flush_dep_map, 0, 0, 1, 2, _THIS_IP_);
+#endif

i think the #ifdef should only be needed for the .name initialization - both lock_acquire() and lock_release() maps to NOP if PROVE_LOCKING is off.

Ingo

author
#2 lore raw
Quoted 9 lines · Ingo Molnar
Quoted 3 lines · Jarek Poplawski

Here is my patch proposal for detecting possible lockups, when flush_workqueue caller holds a lock (e.g. rtnl_lock) also used in work functions.

looks good in principle - did you test it and it caught a bug that wasnt caught before?

Yes, but it was only my own testing bug... (I'm not a good tester, sorry).

Quoted 6 lines
Quoted 5 lines
kernel/workqueue.c +4 -0
+#ifdef CONFIG_PROVE_LOCKING
+/* Detect possible flush_workqueue() lockup with circular dependency check. */
+static struct lockdep_map flush_dep_map = { .name = "flush_dep_map" };
+#endif
Quoted 8 lines

kernel/workqueue.c static void run_workqueue(struct cpu_wor · line 259

Quoted 4 lines
kernel/workqueue.c +4 -0
+#ifdef CONFIG_PROVE_LOCKING
+		/* lockdep dependency: flush_dep_map (read) before any lock: */
+		lock_acquire(&flush_dep_map, 0, 0, 1, 2, _THIS_IP_);
+#endif

i think the #ifdef should only be needed for the .name initialization - both lock_acquire() and lock_release() maps to NOP if PROVE_LOCKING is off.

There is also DEBUG_LOCK_ALLOC without PROVE_LOCKING possibility, which isn't usable here.

Jarek P.