[PATCH 02/12] workqueue: disallow set_cpus_allowed_ptr() from work item

[Lai Jiangshan]

workers depend on local-wake-up, if a work function change its CPU, it will
corrupt workqueue, disallow this behavior.

When set_cpus_allowed_ptr() is called from workqueue.c in worker_thread(),
we clear the PF_WQ_WORKER before set_cpus_allowed_ptr() and set it back
after. (rescuer thread has no PF_WQ_WORKER, skip this behavior)

It prevents other/future BUGs like https://bugzilla.kernel.org/show_bug.cgi?id=47301.

CC: tangchen <tangchen@xxxxxxxxxxxxxx>
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
 kernel/sched/core.c |    8 +++++---
 kernel/workqueue.c  |   10 +++++++++-
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d325c4b..355d3cc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5187,9 +5187,11 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 		goto out;
 	}
 
-	if (unlikely((p->flags & PF_THREAD_BOUND) && p != current)) {
-		ret = -EINVAL;
-		goto out;
+	if (unlikely(p->flags & PF_THREAD_BOUND)) {
+		if (WARN_ON_ONCE(p->flags & PF_WQ_WORKER) || p != current) {
+			ret = -EINVAL;
+			goto out;
+		}
 	}
 
 	do_set_cpus_allowed(p, new_mask);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ec882a6..c55884d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1600,6 +1600,7 @@ __acquires(&gcwq->lock)
 	struct global_cwq *gcwq = worker->pool->gcwq;
 	struct task_struct *task = worker->task;
 
+	BUG_ON(task != current);
 	while (true) {
 		/*
 		 * The following call may fail, succeed or succeed
@@ -1607,9 +1608,16 @@ __acquires(&gcwq->lock)
 		 * it races with cpu hotunplug operation.  Verify
 		 * against GCWQ_DISASSOCIATED.
 		 */
-		if (!(gcwq->flags & GCWQ_DISASSOCIATED))
+		if (!(gcwq->flags & GCWQ_DISASSOCIATED)) {
+			if (!(worker->flags & WORKER_RESCUER))
+				task->flags &= ~PF_WQ_WORKER;
+
 			set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu));
 
+			if (!(worker->flags & WORKER_RESCUER))
+				task->flags |= PF_WQ_WORKER;
+		}
+
 		spin_lock_irq(&gcwq->lock);
 		if (gcwq->flags & GCWQ_DISASSOCIATED)
 			return false;
-- 
1.7.7.6

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