[PATCH] io_uring: drop the old style inflight file tracking

[Jens Axboe <axboe@kernel.dk>]

io_uring tracks requests that are referencing an io_uring descriptor to
be able to cancel without worrying about loops in the references. Since
we now assign the file at execution time, the easier approach is to drop
a potentially problematic reference before we punt the request. This
eliminates the need to special case these types of files beyond just
marking them as such.

This also fixes a recent issue where an async punted tee operation would
with the io_uring descriptor as the output file would crash when
attempting to get a reference to the file from the io-wq worker. We
could have worked around that, but this is the much cleaner fix.

Fixes: 734a69489dd7 ("io_uring: defer file assignment")
Reported-by: syzbot+c4b9303500a21750b250@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 00bc123ab5e7..1b929ca181a0 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -501,7 +501,6 @@ struct io_uring_task {
 	const struct io_ring_ctx *last;
 	struct io_wq		*io_wq;
 	struct percpu_counter	inflight;
-	atomic_t		inflight_tracked;
 	atomic_t		in_idle;
 
 	spinlock_t		task_lock;
@@ -1190,6 +1189,7 @@ static int __io_register_rsrc_update(struct io_ring_ctx *ctx, unsigned type,
 static void io_clean_op(struct io_kiocb *req);
 static struct file *io_file_get(struct io_ring_ctx *ctx,
 				struct io_kiocb *req, int fd, bool fixed);
+static void io_drop_inflight_file(struct io_kiocb *req);
 static void __io_queue_sqe(struct io_kiocb *req);
 static void io_rsrc_put_work(struct work_struct *work);
 
@@ -1642,14 +1642,6 @@ static inline bool io_req_ffs_set(struct io_kiocb *req)
 	return req->flags & REQ_F_FIXED_FILE;
 }
 
-static inline void io_req_track_inflight(struct io_kiocb *req)
-{
-	if (!(req->flags & REQ_F_INFLIGHT)) {
-		req->flags |= REQ_F_INFLIGHT;
-		atomic_inc(&current->io_uring->inflight_tracked);
-	}
-}
-
 static struct io_kiocb *__io_prep_linked_timeout(struct io_kiocb *req)
 {
 	if (WARN_ON_ONCE(!req->link))
@@ -2560,6 +2552,8 @@ static void io_req_task_work_add(struct io_kiocb *req, bool priority)
 
 	WARN_ON_ONCE(!tctx);
 
+	io_drop_inflight_file(req);
+
 	spin_lock_irqsave(&tctx->task_lock, flags);
 	if (priority)
 		wq_list_add_tail(&req->io_task_work.node, &tctx->prior_task_list);
@@ -7198,11 +7192,6 @@ static void io_clean_op(struct io_kiocb *req)
 		kfree(req->apoll);
 		req->apoll = NULL;
 	}
-	if (req->flags & REQ_F_INFLIGHT) {
-		struct io_uring_task *tctx = req->task->io_uring;
-
-		atomic_dec(&tctx->inflight_tracked);
-	}
 	if (req->flags & REQ_F_CREDS)
 		put_cred(req->creds);
 	if (req->flags & REQ_F_ASYNC_DATA) {
@@ -7487,6 +7476,19 @@ static inline struct file *io_file_get_fixed(struct io_ring_ctx *ctx,
 	return file;
 }
 
+/*
+ * Drop the file for requeue operations. Only used of req->file is the
+ * io_uring descriptor itself.
+ */
+static void io_drop_inflight_file(struct io_kiocb *req)
+{
+	if (unlikely(req->flags & REQ_F_INFLIGHT)) {
+		fput(req->file);
+		req->file = NULL;
+		req->flags &= ~REQ_F_INFLIGHT;
+	}
+}
+
 static struct file *io_file_get_normal(struct io_ring_ctx *ctx,
 				       struct io_kiocb *req, int fd)
 {
@@ -7495,8 +7497,8 @@ static struct file *io_file_get_normal(struct io_ring_ctx *ctx,
 	trace_io_uring_file_get(ctx, req, req->user_data, fd);
 
 	/* we don't allow fixed io_uring files */
-	if (file && unlikely(file->f_op == &io_uring_fops))
-		io_req_track_inflight(req);
+	if (unlikely(file && unlikely(file->f_op == &io_uring_fops)))
+		req->flags |= REQ_F_INFLIGHT;
 	return file;
 }
 
@@ -9412,7 +9414,6 @@ static __cold int io_uring_alloc_task_context(struct task_struct *task,
 	xa_init(&tctx->xa);
 	init_waitqueue_head(&tctx->wait);
 	atomic_set(&tctx->in_idle, 0);
-	atomic_set(&tctx->inflight_tracked, 0);
 	task->io_uring = tctx;
 	spin_lock_init(&tctx->task_lock);
 	INIT_WQ_LIST(&tctx->task_list);
@@ -10605,7 +10606,7 @@ static __cold void io_uring_clean_tctx(struct io_uring_task *tctx)
 static s64 tctx_inflight(struct io_uring_task *tctx, bool tracked)
 {
 	if (tracked)
-		return atomic_read(&tctx->inflight_tracked);
+		return 0;
 	return percpu_counter_sum(&tctx->inflight);
 }
 
-- 
Jens Axboe