add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/mm/backing-dev.c
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@@ -378,6 +378,15 @@
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 static DEFINE_SPINLOCK(cgwb_lock);
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 static struct workqueue_struct *cgwb_release_wq;
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+static void cgwb_free_rcu(struct rcu_head *rcu_head)
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+{
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+	struct bdi_writeback *wb = container_of(rcu_head,
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+			struct bdi_writeback, rcu);
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+
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+	percpu_ref_exit(&wb->refcnt);
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+	kfree(wb);
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+}
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+
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 static void cgwb_release_workfn(struct work_struct *work)
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 {
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 	struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
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@@ -395,9 +404,8 @@
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 	blkcg_unpin_online(blkcg);
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 	fprop_local_destroy_percpu(&wb->memcg_completions);
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-	percpu_ref_exit(&wb->refcnt);
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 	wb_exit(wb);
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-	kfree_rcu(wb, rcu);
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+	call_rcu(&wb->rcu, cgwb_free_rcu);
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 }
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 static void cgwb_release(struct percpu_ref *refcnt)