linux-kernel - Re: [PATCH v2 1/2] io_uring: Add new functions to handle user fault scenarios

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Message-ID: <CANHzP_tGxKmcQpVZOt077a-MYb3YHLcZvZDcFxsha4BLt1y16g@mail.gmail.com>
Date: Thu, 24 Apr 2025 00:07:19 +0800
From: 姜智伟 <qq282012236@...il.com>
To: Jens Axboe <axboe@...nel.dk>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz, 
	akpm@...ux-foundation.org, peterx@...hat.com, asml.silence@...il.com, 
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, io-uring@...r.kernel.org
Subject: Re: [PATCH v2 1/2] io_uring: Add new functions to handle user fault scenarios

Jens Axboe <axboe@...nel.dk> 于2025年4月23日周三 23:55写道：
>
> Something like this, perhaps - it'll ensure that io-wq workers get a
> chance to flush out pending work, which should prevent the looping. I've
> attached a basic test case. It'll issue a write that will fault, and
> then try and cancel that as a way to trigger the TIF_NOTIFY_SIGNAL based
> looping.
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index d80f94346199..e18926dbf20a 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -32,6 +32,7 @@
>  #include <linux/swapops.h>
>  #include <linux/miscdevice.h>
>  #include <linux/uio.h>
> +#include <linux/io_uring.h>
>
>  static int sysctl_unprivileged_userfaultfd __read_mostly;
>
> @@ -376,6 +377,8 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
>          */
>         if (current->flags & (PF_EXITING|PF_DUMPCORE))
>                 goto out;
> +       else if (current->flags & PF_IO_WORKER)
> +               io_worker_fault();
>
>         assert_fault_locked(vmf);
>
> diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
> index 85fe4e6b275c..d93dd7402a28 100644
> --- a/include/linux/io_uring.h
> +++ b/include/linux/io_uring.h
> @@ -28,6 +28,7 @@ static inline void io_uring_free(struct task_struct *tsk)
>         if (tsk->io_uring)
>                 __io_uring_free(tsk);
>  }
> +void io_worker_fault(void);
>  #else
>  static inline void io_uring_task_cancel(void)
>  {
> @@ -46,6 +47,9 @@ static inline bool io_is_uring_fops(struct file *file)
>  {
>         return false;
>  }
> +static inline void io_worker_fault(void)
> +{
> +}
>  #endif
>
>  #endif
> diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
> index d52069b1177b..f74bea028ec7 100644
> --- a/io_uring/io-wq.c
> +++ b/io_uring/io-wq.c
> @@ -1438,3 +1438,13 @@ static __init int io_wq_init(void)
>         return 0;
>  }
>  subsys_initcall(io_wq_init);
> +
> +void io_worker_fault(void)
> +{
> +       if (test_thread_flag(TIF_NOTIFY_SIGNAL))
> +               clear_notify_signal();
> +       if (test_thread_flag(TIF_NOTIFY_RESUME))
> +               resume_user_mode_work(NULL);
> +       if (task_work_pending(current))
> +               task_work_run();
> +}
>
> --
> Jens Axboe
I understand some of what you said. I was indeed lost in appearances.
It's very late here now, and I'll take a deeper look tomorrow.
Thank you very much.