[PATCH v2] io_uring: remove req cancel in ->flush()

[PATCH v2] io_uring: remove req cancel in ->flush()

[Pavel Begunkov]

Every close(io_uring) causes cancellation of all inflight requests
carrying ->files. That's not nice but was neccessary up until recently.
Now task->files removal is handled in the core code, so that part of
flush can be removed.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
v2: move exiting checks into io_uring_attempt_task_drop() (Jens)
    remove not needed __io_uring_attempt_task_drop()

 fs/io_uring.c | 28 +++++-----------------------
 1 file changed, 5 insertions(+), 23 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 754363ff3ad6..29170bbdd708 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8668,19 +8668,11 @@ static void io_uring_del_task_file(struct file *file)
 		fput(file);
 }
 
-static void __io_uring_attempt_task_drop(struct file *file)
-{
-	struct file *old = xa_load(&current->io_uring->xa, (unsigned long)file);
-
-	if (old == file)
-		io_uring_del_task_file(file);
-}
-
 /*
  * Drop task note for this file if we're the only ones that hold it after
  * pending fput()
  */
-static void io_uring_attempt_task_drop(struct file *file, bool exiting)
+static void io_uring_attempt_task_drop(struct file *file)
 {
 	if (!current->io_uring)
 		return;
@@ -8688,10 +8680,9 @@ static void io_uring_attempt_task_drop(struct file *file, bool exiting)
 	 * fput() is pending, will be 2 if the only other ref is our potential
 	 * task file note. If the task is exiting, drop regardless of count.
 	 */
-	if (!exiting && atomic_long_read(&file->f_count) != 2)
-		return;
-
-	__io_uring_attempt_task_drop(file);
+	if (fatal_signal_pending(current) || (current->flags & PF_EXITING) ||
+	    atomic_long_read(&file->f_count) == 2)
+		io_uring_del_task_file(file);
 }
 
 void __io_uring_files_cancel(struct files_struct *files)
@@ -8749,16 +8740,7 @@ void __io_uring_task_cancel(void)
 
 static int io_uring_flush(struct file *file, void *data)
 {
-	struct io_ring_ctx *ctx = file->private_data;
-
-	/*
-	 * If the task is going away, cancel work it may have pending
-	 */
-	if (fatal_signal_pending(current) || (current->flags & PF_EXITING))
-		data = NULL;
-
-	io_uring_cancel_task_requests(ctx, data);
-	io_uring_attempt_task_drop(file, !data);
+	io_uring_attempt_task_drop(file);
 	return 0;
 }
 
-- 
2.24.0

Re: [PATCH v2] io_uring: remove req cancel in ->flush()

[Jeff Moyer]

Pavel Begunkov <asml.silence@gmail.com> writes:

> Every close(io_uring) causes cancellation of all inflight requests
> carrying ->files. That's not nice but was neccessary up until recently.
> Now task->files removal is handled in the core code, so that part of
> flush can be removed.

I don't understand the motivation for this patch.  Why would an
application close the io_uring fd with outstanding requests?

-Jeff

>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> v2: move exiting checks into io_uring_attempt_task_drop() (Jens)
>     remove not needed __io_uring_attempt_task_drop()
>
>  fs/io_uring.c | 28 +++++-----------------------
>  1 file changed, 5 insertions(+), 23 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 754363ff3ad6..29170bbdd708 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -8668,19 +8668,11 @@ static void io_uring_del_task_file(struct file *file)
>  		fput(file);
>  }
>  
> -static void __io_uring_attempt_task_drop(struct file *file)
> -{
> -	struct file *old = xa_load(&current->io_uring->xa, (unsigned long)file);
> -
> -	if (old == file)
> -		io_uring_del_task_file(file);
> -}
> -
>  /*
>   * Drop task note for this file if we're the only ones that hold it after
>   * pending fput()
>   */
> -static void io_uring_attempt_task_drop(struct file *file, bool exiting)
> +static void io_uring_attempt_task_drop(struct file *file)
>  {
>  	if (!current->io_uring)
>  		return;
> @@ -8688,10 +8680,9 @@ static void io_uring_attempt_task_drop(struct file *file, bool exiting)
>  	 * fput() is pending, will be 2 if the only other ref is our potential
>  	 * task file note. If the task is exiting, drop regardless of count.
>  	 */
> -	if (!exiting && atomic_long_read(&file->f_count) != 2)
> -		return;
> -
> -	__io_uring_attempt_task_drop(file);
> +	if (fatal_signal_pending(current) || (current->flags & PF_EXITING) ||
> +	    atomic_long_read(&file->f_count) == 2)
> +		io_uring_del_task_file(file);
>  }
>  
>  void __io_uring_files_cancel(struct files_struct *files)
> @@ -8749,16 +8740,7 @@ void __io_uring_task_cancel(void)
>  
>  static int io_uring_flush(struct file *file, void *data)
>  {
> -	struct io_ring_ctx *ctx = file->private_data;
> -
> -	/*
> -	 * If the task is going away, cancel work it may have pending
> -	 */
> -	if (fatal_signal_pending(current) || (current->flags & PF_EXITING))
> -		data = NULL;
> -
> -	io_uring_cancel_task_requests(ctx, data);
> -	io_uring_attempt_task_drop(file, !data);
> +	io_uring_attempt_task_drop(file);
>  	return 0;
>  }

Re: [PATCH v2] io_uring: remove req cancel in ->flush()

[Jens Axboe]

On 10/22/20 11:52 AM, Jeff Moyer wrote:
> Pavel Begunkov <asml.silence@gmail.com> writes:
> 
>> Every close(io_uring) causes cancellation of all inflight requests
>> carrying ->files. That's not nice but was neccessary up until recently.
>> Now task->files removal is handled in the core code, so that part of
>> flush can be removed.
> 
> I don't understand the motivation for this patch.  Why would an
> application close the io_uring fd with outstanding requests?

It normally wouldn't, of course. It's important to understand that this
triggers for _any_ close. So if the app did a dup+close, then it'd
still trigger.

The point is that previously we _had_ to cancel requests that had
->files assigned, due to using a weak reference. Now we no longer have
to, so the point is to just get rid of that previous oddity.

-- 
Jens Axboe

Re: [PATCH v2] io_uring: remove req cancel in ->flush()

[Jeff Moyer]

Jens Axboe <axboe@kernel.dk> writes:

> On 10/22/20 11:52 AM, Jeff Moyer wrote:
>> Pavel Begunkov <asml.silence@gmail.com> writes:
>> 
>>> Every close(io_uring) causes cancellation of all inflight requests
>>> carrying ->files. That's not nice but was neccessary up until recently.
>>> Now task->files removal is handled in the core code, so that part of
>>> flush can be removed.
>> 
>> I don't understand the motivation for this patch.  Why would an
>> application close the io_uring fd with outstanding requests?
>
> It normally wouldn't, of course. It's important to understand that this
> triggers for _any_ close. So if the app did a dup+close, then it'd
> still trigger.

Ah, I see.  That makes more sense, thanks.

-Jeff

Re: [PATCH v2] io_uring: remove req cancel in ->flush()

[Jens Axboe]

On 10/22/20 9:38 AM, Pavel Begunkov wrote:
> Every close(io_uring) causes cancellation of all inflight requests
> carrying ->files. That's not nice but was neccessary up until recently.
> Now task->files removal is handled in the core code, so that part of
> flush can be removed.

Applied, thanks.

-- 
Jens Axboe