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 <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From dfea9fce29fda6f2f91161677e0e0d9b671bc099 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@xxxxxxxxx>
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().
Fixes: 0f2122045b946 ("io_uring: don't rely on weak ->files references")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.5+
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 8cf6f22afc5e..b74957856e68 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -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)
