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

[Gang He]

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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