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From: Hao Xu <haoxu@linux.alibaba.com>
To: Pavel Begunkov <asml.silence@gmail.com>, Jens Axboe <axboe@kernel.dk>
Cc: io-uring@vger.kernel.org, Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: Re: [PATCH 2/2] io_uring: fix race between poll completion and cancel_hash insertion
Date: Wed, 15 Sep 2021 18:50:49 +0800	[thread overview]
Message-ID: <7db1302e-4064-73db-5c3e-bc98c03e54c4@linux.alibaba.com> (raw)
In-Reply-To: <b4d71d4e-187d-c96e-2122-e50362c8ead0@gmail.com>

在 2021/9/15 下午6:12, 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[].
>>
>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>> ---
>>
>> Didn't find the exact commit to add Fixes: for..
>>
>>   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;
> 
> Only poll request has req->poll. E.g. it overwrites parts of req->rw.kiocb,
> I guess .ki_complete in particular.
> 
> struct async_poll *apoll = req->apoll;
> apoll->poll.done = true;
Thanks!
> 
> 
>>   	spin_unlock(&ctx->completion_lock);
>>   
>>   	if (!READ_ONCE(apoll->poll.canceled))
>>
> 


      reply	other threads:[~2021-09-15 10:51 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-12 16:23 [PATCH 0/2] poll fixes Hao Xu
2021-09-12 16:23 ` [PATCH 1/2] io_uring: fix tw list mess-up by adding tw while it's already in tw list Hao Xu
2021-09-15  9:44   ` Pavel Begunkov
2021-09-15 10:48     ` Hao Xu
2021-09-26  9:48       ` Hao Xu
2021-09-29 11:16         ` Pavel Begunkov
2021-09-12 16:23 ` [PATCH 2/2] io_uring: fix race between poll completion and cancel_hash insertion Hao Xu
2021-09-15  9:50   ` Pavel Begunkov
2021-09-15 10:49     ` Hao Xu
2021-09-15 10:12   ` Pavel Begunkov
2021-09-15 10:50     ` Hao Xu [this message]

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