Merge tag 'io_uring-5.9-2020-10-02' of git://git.kernel.dk/linux-block

Pull io_uring fixes from Jens Axboe:

 - fix for async buffered reads if read-ahead is fully disabled (Hao)

 - double poll match fix

 - ->show_fdinfo() potential ABBA deadlock complaint fix

* tag 'io_uring-5.9-2020-10-02' of git://git.kernel.dk/linux-block:
  io_uring: fix async buffered reads when readahead is disabled
  io_uring: fix potential ABBA deadlock in ->show_fdinfo()
  io_uring: always delete double poll wait entry on match

Author: torvalds

fs/io_uring.c

@@ -3049,6 +3049,7 @@ static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode,
 	if (!wake_page_match(wpq, key))
 		return 0;
 
+	req->rw.kiocb.ki_flags &= ~IOCB_WAITQ;
 	list_del_init(&wait->entry);
 
 	init_task_work(&req->task_work, io_req_task_submit);
@@ -3106,6 +3107,7 @@ static bool io_rw_should_retry(struct io_kiocb *req)
 	wait->wait.flags = 0;
 	INIT_LIST_HEAD(&wait->wait.entry);
 	kiocb->ki_flags |= IOCB_WAITQ;
+	kiocb->ki_flags &= ~IOCB_NOWAIT;
 	kiocb->ki_waitq = wait;
 
 	io_get_req_task(req);
@@ -4743,6 +4745,8 @@ static int io_poll_double_wake(struct wait_queue_entry *wait, unsigned mode,
 	if (mask && !(mask & poll->events))
 		return 0;
 
+	list_del_init(&wait->entry);
+
 	if (poll && poll->head) {
 		bool done;
 
@@ -8412,11 +8416,19 @@ static int io_uring_show_cred(int id, void *p, void *data)
 
 static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 {
+	bool has_lock;
 	int i;
 
-	mutex_lock(&ctx->uring_lock);
+	/*
+	 * Avoid ABBA deadlock between the seq lock and the io_uring mutex,
+	 * since fdinfo case grabs it in the opposite direction of normal use
+	 * cases. If we fail to get the lock, we just don't iterate any
+	 * structures that could be going away outside the io_uring mutex.
+	 */
+	has_lock = mutex_trylock(&ctx->uring_lock);
+
 	seq_printf(m, "UserFiles:\t%u\n", ctx->nr_user_files);
-	for (i = 0; i < ctx->nr_user_files; i++) {
+	for (i = 0; has_lock && i < ctx->nr_user_files; i++) {
 		struct fixed_file_table *table;
 		struct file *f;
 
@@ -8428,13 +8440,13 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 			seq_printf(m, "%5u: <none>\n", i);
 	}
 	seq_printf(m, "UserBufs:\t%u\n", ctx->nr_user_bufs);
-	for (i = 0; i < ctx->nr_user_bufs; i++) {
+	for (i = 0; has_lock && i < ctx->nr_user_bufs; i++) {
 		struct io_mapped_ubuf *buf = &ctx->user_bufs[i];
 
 		seq_printf(m, "%5u: 0x%llx/%u\n", i, buf->ubuf,
 						(unsigned int) buf->len);
 	}
-	if (!idr_is_empty(&ctx->personality_idr)) {
+	if (has_lock && !idr_is_empty(&ctx->personality_idr)) {
 		seq_printf(m, "Personalities:\n");
 		idr_for_each(&ctx->personality_idr, io_uring_show_cred, m);
 	}
@@ -8449,7 +8461,8 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 					req->task->task_works != NULL);
 	}
 	spin_unlock_irq(&ctx->completion_lock);
-	mutex_unlock(&ctx->uring_lock);
+	if (has_lock)
+		mutex_unlock(&ctx->uring_lock);
 }
 
 static void io_uring_show_fdinfo(struct seq_file *m, struct file *f)

mm/filemap.c

@@ -2365,7 +2365,11 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
 		}
 
 		if (!PageUptodate(page)) {
-			error = lock_page_killable(page);
+			if (iocb->ki_flags & IOCB_WAITQ)
+				error = lock_page_async(page, iocb->ki_waitq);
+			else
+				error = lock_page_killable(page);
+
 			if (unlikely(error))
 				goto readpage_error;
 			if (!PageUptodate(page)) {