Re: [PATCH 2/2] io_uring: don't hold uring_lock when calling io_run_task_work*

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/2/4 上午12:45, Pavel Begunkov 写道:
> On 03/02/2021 16:35, Pavel Begunkov wrote:
>> On 03/02/2021 14:57, Hao Xu wrote:
>>> This is caused by calling io_run_task_work_sig() to do work under
>>> uring_lock while the caller io_sqe_files_unregister() already held
>>> uring_lock.
>>> we need to check if uring_lock is held by us when doing unlock around
>>> io_run_task_work_sig() since there are code paths down to that place
>>> without uring_lock held.
>>
>> 1. we don't want to allow parallel io_sqe_files_unregister()s
>> happening, it's synchronised by uring_lock atm. Otherwise it's
>> buggy.
Here "since there are code paths down to that place without uring_lock 
held" I mean code path of io_ring_ctx_free().
> 
> This one should be simple, alike to
> 
> if (percpu_refs_is_dying())
> 	return error; // fail *files_unregister();
> 
>>
>> 2. probably same with unregister and submit.
>>
>>>
>>> Reported-by: Abaci <abaci@linux.alibaba.com>
>>> Fixes: 1ffc54220c44 ("io_uring: fix io_sqe_files_unregister() hangs")
>>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>>> ---
>>>   fs/io_uring.c | 19 +++++++++++++------
>>>   1 file changed, 13 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>> index efb6d02fea6f..b093977713ee 100644
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -7362,18 +7362,25 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx, bool locked)
>>>   
>>>   	/* wait for all refs nodes to complete */
>>>   	flush_delayed_work(&ctx->file_put_work);
>>> +	if (locked)
>>> +		mutex_unlock(&ctx->uring_lock);
>>>   	do {
>>>   		ret = wait_for_completion_interruptible(&data->done);
>>>   		if (!ret)
>>>   			break;
>>>   		ret = io_run_task_work_sig();
>>> -		if (ret < 0) {
>>> -			percpu_ref_resurrect(&data->refs);
>>> -			reinit_completion(&data->done);
>>> -			io_sqe_files_set_node(data, backup_node);
>>> -			return ret;
>>> -		}
>>> +		if (ret < 0)
>>> +			break;
>>>   	} while (1);
>>> +	if (locked)
>>> +		mutex_lock(&ctx->uring_lock);
>>> +
>>> +	if (ret < 0) {
>>> +		percpu_ref_resurrect(&data->refs);
>>> +		reinit_completion(&data->done);
>>> +		io_sqe_files_set_node(data, backup_node);
>>> +		return ret;
>>> +	}
>>>   
>>>   	__io_sqe_files_unregister(ctx);
>>>   	nr_tables = DIV_ROUND_UP(ctx->nr_user_files, IORING_MAX_FILES_TABLE);
>>>
>>
>