Re: [PATCH 2/2] io_uring: fix race between poll completion and cancel_hash insertion

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

在 2021/9/15 下午5:50, Pavel Begunkov 写道:
> On 9/12/21 5:23 PM, Hao Xu wrote:
>> If poll arming and poll completion runs parallelly, there maybe races.
>> For instance, run io_poll_add in iowq and io_poll_task_func in original
>> context, then:
>>               iowq                          original context
>>    io_poll_add
>>      vfs_poll
>>       (interruption happens
>>        tw queued to original
>>        context)                              io_poll_task_func
>>                                                generate cqe
>>                                                del from cancel_hash[]
>>      if !poll.done
>>        insert to cancel_hash[]
>>
>> The entry left in cancel_hash[], similar case for fast poll.
>> Fix it by set poll.done = true when del from cancel_hash[].
> 
> Sounds like a valid concern. And the code looks good, but one
> of two patches crashed the kernel somewhere in io_read().
> 
> ./232c93d07b74-test
I'll run it too, didn't meet that when I did the test.
> 
> will be retesting
> 
> 
>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>> ---
>>
>> Didn't find the exact commit to add Fixes: for..
> 
> That's ok. Maybe you can find which kernel versions are
> affected? So we can add stable and specify where it should
> be backported? E.g.
Sure, will do that.
> 
> Cc: stable@vger.kernel.org # 5.12+
> 
> 
>>   fs/io_uring.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index c16f6be3d46b..988679e5063f 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -5118,10 +5118,8 @@ static bool __io_poll_complete(struct io_kiocb *req, __poll_t mask)
>>   	}
>>   	if (req->poll.events & EPOLLONESHOT)
>>   		flags = 0;
>> -	if (!io_cqring_fill_event(ctx, req->user_data, error, flags)) {
>> -		req->poll.done = true;
>> +	if (!io_cqring_fill_event(ctx, req->user_data, error, flags))
>>   		flags = 0;
>> -	}
>>   	if (flags & IORING_CQE_F_MORE)
>>   		ctx->cq_extra++;
>>   
>> @@ -5152,6 +5150,7 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
>>   		if (done) {
>>   			io_poll_remove_double(req);
>>   			hash_del(&req->hash_node);
>> +			req->poll.done = true;
>>   		} else {
>>   			req->result = 0;
>>   			add_wait_queue(req->poll.head, &req->poll.wait);
>> @@ -5289,6 +5288,7 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked)
>>   
>>   	hash_del(&req->hash_node);
>>   	io_poll_remove_double(req);
>> +	req->poll.done = true;
>>   	spin_unlock(&ctx->completion_lock);
>>   
>>   	if (!READ_ONCE(apoll->poll.canceled))
>>
>