linux-kernel - Re: [RFC PATCH] io_uring: stop issue failed request to fix panic

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Date:   Wed, 1 Sep 2021 10:47:15 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     王贇 <yun.wang@...ux.alibaba.com>,
        Jens Axboe <axboe@...nel.dk>,
        "open list:IO_URING" <io-uring@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] io_uring: stop issue failed request to fix panic

On 9/1/21 10:39 AM, 王贇 wrote:
> We observed panic:
>   BUG: kernel NULL pointer dereference, address:0000000000000028
>   [skip]
>   Oops: 0000 [#1] SMP PTI
>   CPU: 1 PID: 737 Comm: a.out Not tainted 5.14.0+ #58
>   Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
>   RIP: 0010:vfs_fadvise+0x1e/0x80
>   [skip]
>   Call Trace:
>    ? tctx_task_work+0x111/0x2a0
>    io_issue_sqe+0x524/0x1b90

Most likely it was fixed yesterday. Can you try?
https://git.kernel.dk/cgit/linux-block/log/?h=for-5.15/io_uring

Or these two patches in particular

https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.15/io_uring&id=c6d3d9cbd659de8f2176b4e4721149c88ac096d4
https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.15/io_uring&id=b8ce1b9d25ccf81e1bbabd45b963ed98b2222df8

> This is caused by io_wq_submit_work() calling io_issue_sqe()
> on a failed fadvise request, and the io_init_req() return error
> before initialize the file for it, lead into the panic when
> vfs_fadvise() try to access 'req->file'.
> 
> This patch add the missing check & handle for failed request
> before calling io_issue_sqe().
> 
> Signed-off-by: Michael Wang <yun.wang@...ux.alibaba.com>
> ---
>  fs/io_uring.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 6f35b12..bfec7bf 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2214,7 +2214,8 @@ static void io_req_task_submit(struct io_kiocb *req, bool *locked)
> 
>  	io_tw_lock(ctx, locked);
>  	/* req->task == current here, checking PF_EXITING is safe */
> -	if (likely(!(req->task->flags & PF_EXITING)))
> +	if (likely(!(req->task->flags & PF_EXITING) &&
> +		   !(req->flags & REQ_F_FAIL)))
>  		__io_queue_sqe(req);
>  	else
>  		io_req_complete_failed(req, -EFAULT);
> @@ -6704,7 +6705,10 @@ static void io_wq_submit_work(struct io_wq_work *work)
> 
>  	if (!ret) {
>  		do {
> -			ret = io_issue_sqe(req, 0);
> +			if (likely(!(req->flags & REQ_F_FAIL)))
> +				ret = io_issue_sqe(req, 0);
> +			else
> +				io_req_complete_failed(req, -EFAULT);
>  			/*
>  			 * We can get EAGAIN for polled IO even though we're
>  			 * forcing a sync submission from here, since we can't
> 

-- 
Pavel Begunkov