[Ocfs2-devel] [PATCH] ocfs2: don't use iocb when EIOCBQUEUED returns

[Joseph Qi]

Hi Changwei,

I agree with Gang that currently we still haven't figured out why iocb
was freed. Though you fix won't bring any side effect, it looks like a
workaround.
That means, the freed iocb may still have risk in other place.

Thanks,
Joseph

On 18/5/8 23:23, Changwei Ge wrote:
> Hi Gang,
> 
> I don't think this patch is a workaround trick.
> 
> We do face the risk using freed iocb although it is actually indeed hard 
> to encounter, it still exists.
> 
> So I propose to fix it making ocfs2 more reliable.
> 
> 
> Moreover, this patch has been kept in -mm tree for one month. Can anyone 
> help review it with ack or nack? So I can do some improvement for it. :-)
> 
> 
> Thanks,
> 
> Changwei
> 
> 
> On 04/11/2018 10:51 AM, Gang He wrote:
>> Hi Changwei,
>>
>> The code change just works around the problem, but theoretically the IOCB object should not be freed before which is handled.
>> Anyway, if we can find the root cause behind via some way (e.g. inject delay in some place), the result is more perfect.
>>
>>
>> Thanks
>> Gang
>>
>>
>>> Hi Jun,
>>>
>>> On 2018/4/11 8:52, piaojun wrote:
>>>> Hi Changwei,
>>>>
>>>> It looks like a code bug, and 'iocb' should not be freed at this place.
>>>> Could this BUG reproduced easily?
>>> Actually, it's not easy to be reproduced since IO is much slower than CPU
>>> executing instructions. But the logic here is broken, we'd better fix this.
>>>
>>> Thanks,
>>> Changwei
>>>
>>>> thanks,
>>>> Jun
>>>>
>>>> On 2018/4/10 20:00, Changwei Ge wrote:
>>>>> When -EIOCBQUEUED returns, it means that aio_complete() will be called
>>>>> from dio_complete(), which is an asynchronous progress against write_iter.
>>>>> Generally, IO is a very slow progress than executing instruction, but we
>>>>> still can't take the risk to access a freed iocb.
>>>>>
>>>>> And we do face a BUG crash issue.
>>>>> >From crash tool, iocb is obviously freed already.
>>>>> crash> struct -x kiocb ffff881a350f5900
>>>>> struct kiocb {
>>>>>     ki_filp = 0xffff881a350f5a80,
>>>>>     ki_pos = 0x0,
>>>>>     ki_complete = 0x0,
>>>>>     private = 0x0,
>>>>>     ki_flags = 0x0
>>>>> }
>>>>>
>>>>> And the backtrace shows:
>>>>> ocfs2_file_write_iter+0xcaa/0xd00 [ocfs2]
>>>>> ? ocfs2_check_range_for_refcount+0x150/0x150 [ocfs2]
>>>>> aio_run_iocb+0x229/0x2f0
>>>>> ? try_to_wake_up+0x380/0x380
>>>>> do_io_submit+0x291/0x540
>>>>> ? syscall_trace_leave+0xad/0x130
>>>>> SyS_io_submit+0x10/0x20
>>>>> system_call_fastpath+0x16/0x75
>>>>>
>>>>> Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
>>>>> ---
>>>>>    fs/ocfs2/file.c | 4 ++--
>>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
>>>>> index 5d1784a..1393ff2 100644
>>>>> --- a/fs/ocfs2/file.c
>>>>> +++ b/fs/ocfs2/file.c
>>>>> @@ -2343,7 +2343,7 @@ static ssize_t ocfs2_file_write_iter(struct kiocb
>>> *iocb,
>>>>>    
>>>>>    	written = __generic_file_write_iter(iocb, from);
>>>>>    	/* buffered aio wouldn't have proper lock coverage today */
>>>>> -	BUG_ON(written == -EIOCBQUEUED && !(iocb->ki_flags & IOCB_DIRECT));
>>>>> +	BUG_ON(written == -EIOCBQUEUED && !direct_io);
>>>>>    
>>>>>    	/*
>>>>>    	 * deep in g_f_a_w_n()->ocfs2_direct_IO we pass in a ocfs2_dio_end_io
>>>>> @@ -2463,7 +2463,7 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
>>>>>    	trace_generic_file_aio_read_ret(ret);
>>>>>    
>>>>>    	/* buffered aio wouldn't have proper lock coverage today */
>>>>> -	BUG_ON(ret == -EIOCBQUEUED && !(iocb->ki_flags & IOCB_DIRECT));
>>>>> +	BUG_ON(ret == -EIOCBQUEUED && !direct_io);
>>>>>    
>>>>>    	/* see ocfs2_file_write_iter */
>>>>>    	if (ret == -EIOCBQUEUED || !ocfs2_iocb_is_rw_locked(iocb)) {
>>>>>
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>>> Ocfs2-devel at oss.oracle.com
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>>
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