Re: [PATCH v2] io_uring: fix dead-hung for non-iter fixed rw

[Jackie Liu <jackieliu@byteisland.com>]

> 2019年11月25日 01:52，Pavel Begunkov <asml.silence@gmail.com> 写道：
> 
> On 24/11/2019 20:10, Jens Axboe wrote:
>> On 11/24/19 1:58 AM, Pavel Begunkov wrote:
>>> Read/write requests to devices without implemented read/write_iter
>>> using fixed buffers causes general protection fault, which totally
>>> hangs a machine.
>>> 
>>> io_import_fixed() initialises iov_iter with bvec, but loop_rw_iter()
>>> accesses it as iovec, so dereferencing random address.
>>> 
>>> kmap() page by page in this case
>> 
>> This looks good to me, much cleaner/simpler. I've added a few pipe fixed
>> buffer tests to liburing as well. Didn't crash for me, but obvious
>> garbage coming out. I've flagged this for stable as well.
>> 
> The problem I have is that __user pointer is meant to be checked
> for not being a kernel address. I suspect, it could fail in some
> device, which double checks the pointer after vfs (e.g. using access_ok()).
> Am I wrong? Not a fault at least...
> 
> #define access_ok(...) __range_not_ok(addr, user_addr_max());
> 
> BTW, is there anybody testing it for non x86-64 arch?
> 

I have some aarch64 platform, What test do you want me to do?

--
Jackie Liu