FAILED: patch "[PATCH] io_uring: enable lookup of links holding inflight files" failed to apply to 5.7-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.7-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 <stable@vger.kernel.org>.

thanks,

greg k-h

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

From f254ac04c8744cf7bfed012717eac34eacc65dfb Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Wed, 12 Aug 2020 17:33:30 -0600
Subject: [PATCH] io_uring: enable lookup of links holding inflight files

When a process exits, we cancel whatever requests it has pending that
are referencing the file table. However, if a link is holding a
reference, then we cannot find it by simply looking at the inflight
list.

Enable checking of the poll and timeout list to find the link, and
cancel it appropriately.

Cc: stable@vger.kernel.org
Reported-by: Josef <josef.grieb@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 8a2afd8c33c9..1ec25ee71372 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4937,6 +4937,7 @@ static bool io_poll_remove_one(struct io_kiocb *req)
 		io_cqring_fill_event(req, -ECANCELED);
 		io_commit_cqring(req->ctx);
 		req->flags |= REQ_F_COMP_LOCKED;
+		req_set_fail_links(req);
 		io_put_req(req);
 	}
 
@@ -5109,6 +5110,23 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer)
 	return HRTIMER_NORESTART;
 }
 
+static int __io_timeout_cancel(struct io_kiocb *req)
+{
+	int ret;
+
+	list_del_init(&req->timeout.list);
+
+	ret = hrtimer_try_to_cancel(&req->io->timeout.timer);
+	if (ret == -1)
+		return -EALREADY;
+
+	req_set_fail_links(req);
+	req->flags |= REQ_F_COMP_LOCKED;
+	io_cqring_fill_event(req, -ECANCELED);
+	io_put_req(req);
+	return 0;
+}
+
 static int io_timeout_cancel(struct io_ring_ctx *ctx, __u64 user_data)
 {
 	struct io_kiocb *req;
@@ -5116,7 +5134,6 @@ static int io_timeout_cancel(struct io_ring_ctx *ctx, __u64 user_data)
 
 	list_for_each_entry(req, &ctx->timeout_list, timeout.list) {
 		if (user_data == req->user_data) {
-			list_del_init(&req->timeout.list);
 			ret = 0;
 			break;
 		}
@@ -5125,15 +5142,7 @@ static int io_timeout_cancel(struct io_ring_ctx *ctx, __u64 user_data)
 	if (ret == -ENOENT)
 		return ret;
 
-	ret = hrtimer_try_to_cancel(&req->io->timeout.timer);
-	if (ret == -1)
-		return -EALREADY;
-
-	req_set_fail_links(req);
-	req->flags |= REQ_F_COMP_LOCKED;
-	io_cqring_fill_event(req, -ECANCELED);
-	io_put_req(req);
-	return 0;
+	return __io_timeout_cancel(req);
 }
 
 static int io_timeout_remove_prep(struct io_kiocb *req,
@@ -7935,6 +7944,71 @@ static bool io_wq_files_match(struct io_wq_work *work, void *data)
 	return work->files == files;
 }
 
+/*
+ * Returns true if 'preq' is the link parent of 'req'
+ */
+static bool io_match_link(struct io_kiocb *preq, struct io_kiocb *req)
+{
+	struct io_kiocb *link;
+
+	if (!(preq->flags & REQ_F_LINK_HEAD))
+		return false;
+
+	list_for_each_entry(link, &preq->link_list, link_list) {
+		if (link == req)
+			return true;
+	}
+
+	return false;
+}
+
+/*
+ * We're looking to cancel 'req' because it's holding on to our files, but
+ * 'req' could be a link to another request. See if it is, and cancel that
+ * parent request if so.
+ */
+static bool io_poll_remove_link(struct io_ring_ctx *ctx, struct io_kiocb *req)
+{
+	struct hlist_node *tmp;
+	struct io_kiocb *preq;
+	bool found = false;
+	int i;
+
+	spin_lock_irq(&ctx->completion_lock);
+	for (i = 0; i < (1U << ctx->cancel_hash_bits); i++) {
+		struct hlist_head *list;
+
+		list = &ctx->cancel_hash[i];
+		hlist_for_each_entry_safe(preq, tmp, list, hash_node) {
+			found = io_match_link(preq, req);
+			if (found) {
+				io_poll_remove_one(preq);
+				break;
+			}
+		}
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+	return found;
+}
+
+static bool io_timeout_remove_link(struct io_ring_ctx *ctx,
+				   struct io_kiocb *req)
+{
+	struct io_kiocb *preq;
+	bool found = false;
+
+	spin_lock_irq(&ctx->completion_lock);
+	list_for_each_entry(preq, &ctx->timeout_list, timeout.list) {
+		found = io_match_link(preq, req);
+		if (found) {
+			__io_timeout_cancel(preq);
+			break;
+		}
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+	return found;
+}
+
 static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 				  struct files_struct *files)
 {
@@ -7989,6 +8063,9 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 			}
 		} else {
 			io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
+			/* could be a link, check and remove if it is */
+			if (!io_poll_remove_link(ctx, cancel_req))
+				io_timeout_remove_link(ctx, cancel_req);
 			io_put_req(cancel_req);
 		}