[PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[Hao Xu]

For pure poll requests, we should remove the double poll wait entry.
And io_poll_remove_double() is good enough for it compared with
io_poll_remove_waitqs().

Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
---

v1-->v2
  delete redundant io_poll_remove_double()

 fs/io_uring.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f2fe4eca150b..c5fe8b9e26b4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4903,7 +4903,6 @@ 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)) {
-		io_poll_remove_waitqs(req);
 		req->poll.done = true;
 		flags = 0;
 	}
@@ -4926,6 +4925,7 @@ static void io_poll_task_func(struct io_kiocb *req)
 
 		done = io_poll_complete(req, req->result);
 		if (done) {
+			io_poll_remove_double(req);
 			hash_del(&req->hash_node);
 		} else {
 			req->result = 0;
@@ -5113,7 +5113,7 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
 		ipt->error = -EINVAL;
 
 	spin_lock_irq(&ctx->completion_lock);
-	if (ipt->error)
+	if (ipt->error || (mask && (poll->events & EPOLLONESHOT)))
 		io_poll_remove_double(req);
 	if (likely(poll->head)) {
 		spin_lock(&poll->head->lock);
@@ -5185,7 +5185,6 @@ static int io_arm_poll_handler(struct io_kiocb *req)
 	ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
 					io_async_wake);
 	if (ret || ipt.error) {
-		io_poll_remove_double(req);
 		spin_unlock_irq(&ctx->completion_lock);
 		if (ret)
 			return IO_APOLL_READY;
-- 
2.24.4

Re: [PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[Pavel Begunkov]

On 7/23/21 10:22 AM, Hao Xu wrote:
> For pure poll requests, we should remove the double poll wait entry.
> And io_poll_remove_double() is good enough for it compared with
> io_poll_remove_waitqs().

5.14 in the subject hints me that it's a fix. Is it?
Can you add what it fixes or expand on why it's better?


> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
> 
> v1-->v2
>   delete redundant io_poll_remove_double()
> 
>  fs/io_uring.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index f2fe4eca150b..c5fe8b9e26b4 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -4903,7 +4903,6 @@ 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)) {
> -		io_poll_remove_waitqs(req);
>  		req->poll.done = true;
>  		flags = 0;
>  	}
> @@ -4926,6 +4925,7 @@ static void io_poll_task_func(struct io_kiocb *req)
>  
>  		done = io_poll_complete(req, req->result);
>  		if (done) {
> +			io_poll_remove_double(req);
>  			hash_del(&req->hash_node);
>  		} else {
>  			req->result = 0;
> @@ -5113,7 +5113,7 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
>  		ipt->error = -EINVAL;
>  
>  	spin_lock_irq(&ctx->completion_lock);
> -	if (ipt->error)
> +	if (ipt->error || (mask && (poll->events & EPOLLONESHOT)))
>  		io_poll_remove_double(req);
>  	if (likely(poll->head)) {
>  		spin_lock(&poll->head->lock);
> @@ -5185,7 +5185,6 @@ static int io_arm_poll_handler(struct io_kiocb *req)
>  	ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
>  					io_async_wake);
>  	if (ret || ipt.error) {
> -		io_poll_remove_double(req);
>  		spin_unlock_irq(&ctx->completion_lock);
>  		if (ret)
>  			return IO_APOLL_READY;
> 

-- 
Pavel Begunkov

Re: [PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[Jens Axboe]

On 7/23/21 8:31 AM, Pavel Begunkov wrote:
> On 7/23/21 10:22 AM, Hao Xu wrote:
>> For pure poll requests, we should remove the double poll wait entry.
>> And io_poll_remove_double() is good enough for it compared with
>> io_poll_remove_waitqs().
> 
> 5.14 in the subject hints me that it's a fix. Is it?
> Can you add what it fixes or expand on why it's better?

Ditto that, the commit message explains what is being done, it should
explain _why_ it's being done. For the 'what' part you can read the
code. So while the patch doesn't look wrong, I also can't quite tell why
the change is necessary.

-- 
Jens Axboe

Re: [PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[Hao Xu]

在 2021/7/23 下午10:31, Pavel Begunkov 写道:
> On 7/23/21 10:22 AM, Hao Xu wrote:
>> For pure poll requests, we should remove the double poll wait entry.
>> And io_poll_remove_double() is good enough for it compared with
>> io_poll_remove_waitqs().
> 
> 5.14 in the subject hints me that it's a fix. Is it?
> Can you add what it fixes or expand on why it's better?
Hi Pavel, I found that for poll_add() requests, it doesn't remove the
double poll wait entry when it's done, neither after vfs_poll() or in
the poll completion handler. The patch is mainly to fix it.

> 
> 
>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>> ---
>>
>> v1-->v2
>>    delete redundant io_poll_remove_double()
>>
>>   fs/io_uring.c | 5 ++---
>>   1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index f2fe4eca150b..c5fe8b9e26b4 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -4903,7 +4903,6 @@ 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)) {
>> -		io_poll_remove_waitqs(req);
Currently I only see it does that with io_poll_remove_waitqs() when
cqring overflow and then ocqe allocation failed. Using
io_poll_remove_waitqs() here is not very suitable since (1) it calls
__io_poll_remove_one() which set poll->cancelled = true, why do we set
poll->cancelled and poll->done to true at the same time though I think
that doesn't cause any problem. (2) it does
list_del_init(&poll->wait.entry) and hash_del(&req->hash_node) which
has been already done.
Correct me if I'm wrong since I may misunderstand the code.

Regards,
Hao
>>   		req->poll.done = true;
>>   		flags = 0;
>>   	}
>> @@ -4926,6 +4925,7 @@ static void io_poll_task_func(struct io_kiocb *req)
>>   
>>   		done = io_poll_complete(req, req->result);
>>   		if (done) {
>> +			io_poll_remove_double(req);
>>   			hash_del(&req->hash_node);
>>   		} else {
>>   			req->result = 0;
>> @@ -5113,7 +5113,7 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
>>   		ipt->error = -EINVAL;
>>   
>>   	spin_lock_irq(&ctx->completion_lock);
>> -	if (ipt->error)
>> +	if (ipt->error || (mask && (poll->events & EPOLLONESHOT)))
>>   		io_poll_remove_double(req);
>>   	if (likely(poll->head)) {
>>   		spin_lock(&poll->head->lock);
>> @@ -5185,7 +5185,6 @@ static int io_arm_poll_handler(struct io_kiocb *req)
>>   	ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
>>   					io_async_wake);
>>   	if (ret || ipt.error) {
>> -		io_poll_remove_double(req);
>>   		spin_unlock_irq(&ctx->completion_lock);
>>   		if (ret)
>>   			return IO_APOLL_READY;
>>
> 

Re: [PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[Pavel Begunkov]

On 7/24/21 5:48 AM, Hao Xu wrote:
> 在 2021/7/23 下午10:31, Pavel Begunkov 写道:
>> On 7/23/21 10:22 AM, Hao Xu wrote:
>>> For pure poll requests, we should remove the double poll wait entry.
>>> And io_poll_remove_double() is good enough for it compared with
>>> io_poll_remove_waitqs().
>>
>> 5.14 in the subject hints me that it's a fix. Is it?
>> Can you add what it fixes or expand on why it's better?
> Hi Pavel, I found that for poll_add() requests, it doesn't remove the
> double poll wait entry when it's done, neither after vfs_poll() or in
> the poll completion handler. The patch is mainly to fix it.

Ok, sounds good. Please resend with updated description, and
let's add some tags.

Fixes: 88e41cf928a6 ("io_uring: add multishot mode for IORING_OP_POLL_ADD")
Cc: stable@vger.kernel.org # 5.13+

Also, I'd prefer the commit title to make more clear that it's a
fix. E.g. "io_uring: fix poll requests leaking second poll entries".

Btw, seems it should fix hangs in ./poll-mshot-update


>>
>>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>>> ---
>>>
>>> v1-->v2
>>>    delete redundant io_poll_remove_double()
>>>
>>>   fs/io_uring.c | 5 ++---
>>>   1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>> index f2fe4eca150b..c5fe8b9e26b4 100644
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -4903,7 +4903,6 @@ 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)) {
>>> -        io_poll_remove_waitqs(req);
> Currently I only see it does that with io_poll_remove_waitqs() when
> cqring overflow and then ocqe allocation failed. Using
> io_poll_remove_waitqs() here is not very suitable since (1) it calls
> __io_poll_remove_one() which set poll->cancelled = true, why do we set
> poll->cancelled and poll->done to true at the same time though I think
> that doesn't cause any problem. (2) it does
> list_del_init(&poll->wait.entry) and hash_del(&req->hash_node) which
> has been already done.
> Correct me if I'm wrong since I may misunderstand the code.
> 
> Regards,
> Hao
>>>           req->poll.done = true;
>>>           flags = 0;
>>>       }
>>> @@ -4926,6 +4925,7 @@ static void io_poll_task_func(struct io_kiocb *req)
>>>             done = io_poll_complete(req, req->result);
>>>           if (done) {
>>> +            io_poll_remove_double(req);
>>>               hash_del(&req->hash_node);
>>>           } else {
>>>               req->result = 0;
>>> @@ -5113,7 +5113,7 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
>>>           ipt->error = -EINVAL;
>>>         spin_lock_irq(&ctx->completion_lock);
>>> -    if (ipt->error)
>>> +    if (ipt->error || (mask && (poll->events & EPOLLONESHOT)))
>>>           io_poll_remove_double(req);
>>>       if (likely(poll->head)) {
>>>           spin_lock(&poll->head->lock);
>>> @@ -5185,7 +5185,6 @@ static int io_arm_poll_handler(struct io_kiocb *req)
>>>       ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
>>>                       io_async_wake);
>>>       if (ret || ipt.error) {
>>> -        io_poll_remove_double(req);
>>>           spin_unlock_irq(&ctx->completion_lock);
>>>           if (ret)
>>>               return IO_APOLL_READY;
>>>
>>
> 

-- 
Pavel Begunkov

Re: [PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[Hao Xu]

在 2021/7/26 下午8:40, Pavel Begunkov 写道:
> On 7/24/21 5:48 AM, Hao Xu wrote:
>> 在 2021/7/23 下午10:31, Pavel Begunkov 写道:
>>> On 7/23/21 10:22 AM, Hao Xu wrote:
>>>> For pure poll requests, we should remove the double poll wait entry.
>>>> And io_poll_remove_double() is good enough for it compared with
>>>> io_poll_remove_waitqs().
>>>
>>> 5.14 in the subject hints me that it's a fix. Is it?
>>> Can you add what it fixes or expand on why it's better?
>> Hi Pavel, I found that for poll_add() requests, it doesn't remove the
>> double poll wait entry when it's done, neither after vfs_poll() or in
>> the poll completion handler. The patch is mainly to fix it.
> 
> Ok, sounds good. Please resend with updated description, and
> let's add some tags.
> 
> Fixes: 88e41cf928a6 ("io_uring: add multishot mode for IORING_OP_POLL_ADD")
> Cc: stable@vger.kernel.org # 5.13+
> 
> Also, I'd prefer the commit title to make more clear that it's a
> fix. E.g. "io_uring: fix poll requests leaking second poll entries".
> 
> Btw, seems it should fix hangs in ./poll-mshot-update
Sure，I'll send v3 soon, sorry for my unprofessionalism..
> 
> 
>>>
>>>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>>>> ---
>>>>
>>>> v1-->v2
>>>>     delete redundant io_poll_remove_double()
>>>>
>>>>    fs/io_uring.c | 5 ++---
>>>>    1 file changed, 2 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>> index f2fe4eca150b..c5fe8b9e26b4 100644
>>>> --- a/fs/io_uring.c
>>>> +++ b/fs/io_uring.c
>>>> @@ -4903,7 +4903,6 @@ 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)) {
>>>> -        io_poll_remove_waitqs(req);
>> Currently I only see it does that with io_poll_remove_waitqs() when
>> cqring overflow and then ocqe allocation failed. Using
>> io_poll_remove_waitqs() here is not very suitable since (1) it calls
>> __io_poll_remove_one() which set poll->cancelled = true, why do we set
>> poll->cancelled and poll->done to true at the same time though I think
>> that doesn't cause any problem. (2) it does
>> list_del_init(&poll->wait.entry) and hash_del(&req->hash_node) which
>> has been already done.
>> Correct me if I'm wrong since I may misunderstand the code.
>>
>> Regards,
>> Hao
>>>>            req->poll.done = true;
>>>>            flags = 0;
>>>>        }
>>>> @@ -4926,6 +4925,7 @@ static void io_poll_task_func(struct io_kiocb *req)
>>>>              done = io_poll_complete(req, req->result);
>>>>            if (done) {
>>>> +            io_poll_remove_double(req);
>>>>                hash_del(&req->hash_node);
>>>>            } else {
>>>>                req->result = 0;
>>>> @@ -5113,7 +5113,7 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
>>>>            ipt->error = -EINVAL;
>>>>          spin_lock_irq(&ctx->completion_lock);
>>>> -    if (ipt->error)
>>>> +    if (ipt->error || (mask && (poll->events & EPOLLONESHOT)))
>>>>            io_poll_remove_double(req);
>>>>        if (likely(poll->head)) {
>>>>            spin_lock(&poll->head->lock);
>>>> @@ -5185,7 +5185,6 @@ static int io_arm_poll_handler(struct io_kiocb *req)
>>>>        ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
>>>>                        io_async_wake);
>>>>        if (ret || ipt.error) {
>>>> -        io_poll_remove_double(req);
>>>>            spin_unlock_irq(&ctx->completion_lock);
>>>>            if (ret)
>>>>                return IO_APOLL_READY;
>>>>
>>>
>>
> 

Re: [PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[Jens Axboe]

On 7/26/21 8:39 AM, Hao Xu wrote:
> 在 2021/7/26 下午8:40, Pavel Begunkov 写道:
>> On 7/24/21 5:48 AM, Hao Xu wrote:
>>> 在 2021/7/23 下午10:31, Pavel Begunkov 写道:
>>>> On 7/23/21 10:22 AM, Hao Xu wrote:
>>>>> For pure poll requests, we should remove the double poll wait entry.
>>>>> And io_poll_remove_double() is good enough for it compared with
>>>>> io_poll_remove_waitqs().
>>>>
>>>> 5.14 in the subject hints me that it's a fix. Is it?
>>>> Can you add what it fixes or expand on why it's better?
>>> Hi Pavel, I found that for poll_add() requests, it doesn't remove the
>>> double poll wait entry when it's done, neither after vfs_poll() or in
>>> the poll completion handler. The patch is mainly to fix it.
>>
>> Ok, sounds good. Please resend with updated description, and
>> let's add some tags.
>>
>> Fixes: 88e41cf928a6 ("io_uring: add multishot mode for IORING_OP_POLL_ADD")
>> Cc: stable@vger.kernel.org # 5.13+
>>
>> Also, I'd prefer the commit title to make more clear that it's a
>> fix. E.g. "io_uring: fix poll requests leaking second poll entries".
>>
>> Btw, seems it should fix hangs in ./poll-mshot-update
> Sure，I'll send v3 soon, sorry for my unprofessionalism..

Are you going to send out v3?

-- 
Jens Axboe

Re: [PATCH io_uring-5.14 v2] io_uring: remove double poll wait entry for pure poll

[Hao Xu]

在 2021/7/28 上午6:46, Jens Axboe 写道:
> On 7/26/21 8:39 AM, Hao Xu wrote:
>> 在 2021/7/26 下午8:40, Pavel Begunkov 写道:
>>> On 7/24/21 5:48 AM, Hao Xu wrote:
>>>> 在 2021/7/23 下午10:31, Pavel Begunkov 写道:
>>>>> On 7/23/21 10:22 AM, Hao Xu wrote:
>>>>>> For pure poll requests, we should remove the double poll wait entry.
>>>>>> And io_poll_remove_double() is good enough for it compared with
>>>>>> io_poll_remove_waitqs().
>>>>>
>>>>> 5.14 in the subject hints me that it's a fix. Is it?
>>>>> Can you add what it fixes or expand on why it's better?
>>>> Hi Pavel, I found that for poll_add() requests, it doesn't remove the
>>>> double poll wait entry when it's done, neither after vfs_poll() or in
>>>> the poll completion handler. The patch is mainly to fix it.
>>>
>>> Ok, sounds good. Please resend with updated description, and
>>> let's add some tags.
>>>
>>> Fixes: 88e41cf928a6 ("io_uring: add multishot mode for IORING_OP_POLL_ADD")
>>> Cc: stable@vger.kernel.org # 5.13+
>>>
>>> Also, I'd prefer the commit title to make more clear that it's a
>>> fix. E.g. "io_uring: fix poll requests leaking second poll entries".
>>>
>>> Btw, seems it should fix hangs in ./poll-mshot-update
>> Sure，I'll send v3 soon, sorry for my unprofessionalism..
> 
> Are you going to send out v3?
> 
v3 sent. Btw I'm working on letting fast poll support multishot,
I believe that will benefit non-persistent programming, let's see
if it helps accept().