FAILED: patch "[PATCH] io_uring: close a small race gap for files cancel" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From dfea9fce29fda6f2f91161677e0e0d9b671bc099 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <[email protected]>
Date: Fri, 18 Dec 2020 13:12:21 +0000
Subject: [PATCH] io_uring: close a small race gap for files cancel

The purpose of io_uring_cancel_files() is to wait for all requests matching ->files to go/be cancelled. We should first drop files of a request in io_req_drop_files() and only then make it undiscoverable for io_uring_cancel_files.

First drop, then delete from list. It's ok to leave req->id->files dangling, because it's not dereferenced by cancellation code, only compared against. It would potentially go to sleep and be awaken by following in io_req_drop_files() wake_up().

index 8cf6f22afc5e..b74957856e68 100644
@@ -6098,15 +6098,15 @@ static void io_req_drop_files(struct io_kiocb *req)
 	struct io_uring_task *tctx = req->task->io_uring;
 	unsigned long flags;
 
+	put_files_struct(req->work.identity->files);
+	put_nsproxy(req->work.identity->nsproxy);
 	spin_lock_irqsave(&ctx->inflight_lock, flags);
 	list_del(&req->inflight_entry);
-	if (atomic_read(&tctx->in_idle))
-		wake_up(&tctx->wait);
 	spin_unlock_irqrestore(&ctx->inflight_lock, flags);
 	req->flags &= ~REQ_F_INFLIGHT;
-	put_files_struct(req->work.identity->files);
-	put_nsproxy(req->work.identity->nsproxy);
 	req->work.flags &= ~IO_WQ_WORK_FILES;
+	if (atomic_read(&tctx->in_idle))
+		wake_up(&tctx->wait);
 }
 
 static void __io_clean_op(struct io_kiocb *req)