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* [PATCH] io-wq: Remove unnecessary rcu_read_lock/unlock() in raw spinlock critical section
@ 2021-10-26  3:23 Zqiang
  2021-10-26 10:32 ` Muchun Song
  0 siblings, 1 reply; 4+ messages in thread
From: Zqiang @ 2021-10-26  3:23 UTC (permalink / raw)
  To: axboe, asml.silence, io-uring; +Cc: linux-kernel, Zqiang

Due to raw_spin_lock/unlock() contains preempt_disable/enable() action,
already regarded as RCU critical region, so remove unnecessary
rcu_read_lock/unlock().

Signed-off-by: Zqiang <[email protected]>
---
 fs/io-wq.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index cd88602e2e81..401be005d089 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -855,9 +855,7 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
 	io_wqe_insert_work(wqe, work);
 	clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
 
-	rcu_read_lock();
 	do_create = !io_wqe_activate_free_worker(wqe, acct);
-	rcu_read_unlock();
 
 	raw_spin_unlock(&wqe->lock);
 
-- 
2.17.1


^ permalink raw reply related	[flat|nested] 4+ messages in thread

* Re: [PATCH] io-wq: Remove unnecessary rcu_read_lock/unlock() in raw spinlock critical section
  2021-10-26  3:23 [PATCH] io-wq: Remove unnecessary rcu_read_lock/unlock() in raw spinlock critical section Zqiang
@ 2021-10-26 10:32 ` Muchun Song
  2021-10-26 14:47   ` Jens Axboe
  0 siblings, 1 reply; 4+ messages in thread
From: Muchun Song @ 2021-10-26 10:32 UTC (permalink / raw)
  To: Zqiang; +Cc: Jens Axboe, asml.silence, io-uring, LKML

On Tue, Oct 26, 2021 at 11:23 AM Zqiang <[email protected]> wrote:
>
> Due to raw_spin_lock/unlock() contains preempt_disable/enable() action,
> already regarded as RCU critical region, so remove unnecessary
> rcu_read_lock/unlock().
>
> Signed-off-by: Zqiang <[email protected]>
> ---
>  fs/io-wq.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index cd88602e2e81..401be005d089 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -855,9 +855,7 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
>         io_wqe_insert_work(wqe, work);
>         clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
>
> -       rcu_read_lock();

Add a comment like:
/* spin_lock can serve as an RCU read-side critical section. */

With that.

Reviewed-by: Muchun Song <[email protected]>

Thanks.

>         do_create = !io_wqe_activate_free_worker(wqe, acct);
> -       rcu_read_unlock();
>
>         raw_spin_unlock(&wqe->lock);
>
> --
> 2.17.1
>

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] io-wq: Remove unnecessary rcu_read_lock/unlock() in raw spinlock critical section
  2021-10-26 10:32 ` Muchun Song
@ 2021-10-26 14:47   ` Jens Axboe
  2021-10-27  7:06     ` Zqiang
  0 siblings, 1 reply; 4+ messages in thread
From: Jens Axboe @ 2021-10-26 14:47 UTC (permalink / raw)
  To: Muchun Song, Zqiang; +Cc: asml.silence, io-uring, LKML

On 10/26/21 4:32 AM, Muchun Song wrote:
> On Tue, Oct 26, 2021 at 11:23 AM Zqiang <[email protected]> wrote:
>>
>> Due to raw_spin_lock/unlock() contains preempt_disable/enable() action,
>> already regarded as RCU critical region, so remove unnecessary
>> rcu_read_lock/unlock().
>>
>> Signed-off-by: Zqiang <[email protected]>
>> ---
>>  fs/io-wq.c | 2 --
>>  1 file changed, 2 deletions(-)
>>
>> diff --git a/fs/io-wq.c b/fs/io-wq.c
>> index cd88602e2e81..401be005d089 100644
>> --- a/fs/io-wq.c
>> +++ b/fs/io-wq.c
>> @@ -855,9 +855,7 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
>>         io_wqe_insert_work(wqe, work);
>>         clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
>>
>> -       rcu_read_lock();
> 
> Add a comment like:
> /* spin_lock can serve as an RCU read-side critical section. */

Note that it's a raw spinlock. Honestly I'd probably prefer if we just leave
it as-is. There are plans to improve the io-wq locking, and a rcu lock/unlock
is pretty cheap.

That said, if resend with a comment fully detailing why it's OK currently,
then I'd be fine with that as well.

-- 
Jens Axboe


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] io-wq: Remove unnecessary rcu_read_lock/unlock() in raw spinlock critical section
  2021-10-26 14:47   ` Jens Axboe
@ 2021-10-27  7:06     ` Zqiang
  0 siblings, 0 replies; 4+ messages in thread
From: Zqiang @ 2021-10-27  7:06 UTC (permalink / raw)
  To: Jens Axboe, Muchun Song; +Cc: asml.silence, io-uring, LKML


On 2021/10/26 下午10:47, Jens Axboe wrote:
> On 10/26/21 4:32 AM, Muchun Song wrote:
>> On Tue, Oct 26, 2021 at 11:23 AM Zqiang <[email protected]> wrote:
>>> Due to raw_spin_lock/unlock() contains preempt_disable/enable() action,
>>> already regarded as RCU critical region, so remove unnecessary
>>> rcu_read_lock/unlock().
>>>
>>> Signed-off-by: Zqiang <[email protected]>
>>> ---
>>>   fs/io-wq.c | 2 --
>>>   1 file changed, 2 deletions(-)
>>>
>>> diff --git a/fs/io-wq.c b/fs/io-wq.c
>>> index cd88602e2e81..401be005d089 100644
>>> --- a/fs/io-wq.c
>>> +++ b/fs/io-wq.c
>>> @@ -855,9 +855,7 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
>>>          io_wqe_insert_work(wqe, work);
>>>          clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
>>>
>>> -       rcu_read_lock();
>> Add a comment like:
>> /* spin_lock can serve as an RCU read-side critical section. */
> Note that it's a raw spinlock. Honestly I'd probably prefer if we just leave
> it as-is. There are plans to improve the io-wq locking, and a rcu lock/unlock
> is pretty cheap.
>
> That said, if resend with a comment fully detailing why it's OK currently,
> then I'd be fine with that as well.
>
Thanks Jens Axboe, Muchun

  I  will  add a comment fully detailing and resend.




^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2021-10-27  7:06 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2021-10-26  3:23 [PATCH] io-wq: Remove unnecessary rcu_read_lock/unlock() in raw spinlock critical section Zqiang
2021-10-26 10:32 ` Muchun Song
2021-10-26 14:47   ` Jens Axboe
2021-10-27  7:06     ` Zqiang

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