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

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Date:   Wed, 1 Sep 2021 11:59:33 +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 10:52 AM, 王贇 wrote:
]> On 2021/9/1 下午5:47, Pavel Begunkov wrote:
>> 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
> 
> Yup, it no longer panic :-)

awesome, thanks

> 
> Regards,
> Michael Wang
> 
>>
>>> 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