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

[Pavel Begunkov <asml.silence@gmail.com>]

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.

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);
>>
> 

-- 
Pavel Begunkov