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

[王贇 <yun.wang@linux.alibaba.com>]

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 :-)

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@linux.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
>>
>