From 52504a61ab999289d406f5dec930d3e3f386365d Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Fri, 18 Dec 2020 13:12:21 +0000 Subject: [PATCH] io_uring: close a small race gap for files cancel commit dfea9fce29fda6f2f91161677e0e0d9b671bc099 upstream. 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(). Fixes: 0f2122045b946 ("io_uring: don't rely on weak ->files references") Cc: # 5.5+ Signed-off-by: Pavel Begunkov Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- fs/io_uring.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 0fcd065baa76..96598b6fbc81 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -5861,15 +5861,15 @@ static void io_req_drop_files(struct io_kiocb *req) struct io_ring_ctx *ctx = req->ctx; unsigned long flags; - spin_lock_irqsave(&ctx->inflight_lock, flags); - list_del(&req->inflight_entry); - if (waitqueue_active(&ctx->inflight_wait)) - wake_up(&ctx->inflight_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); + spin_lock_irqsave(&ctx->inflight_lock, flags); + list_del(&req->inflight_entry); + spin_unlock_irqrestore(&ctx->inflight_lock, flags); + req->flags &= ~REQ_F_INFLIGHT; req->work.flags &= ~IO_WQ_WORK_FILES; + if (waitqueue_active(&ctx->inflight_wait)) + wake_up(&ctx->inflight_wait); } static void __io_clean_op(struct io_kiocb *req)