Re: [PATCH 5/6] kernel: better document the use_mm/unuse_mm API contract

[Felix Kuehling <felix.kuehling@amd.com>]

Am 2020-04-04 um 5:41 a.m. schrieb Christoph Hellwig:
> Switch the function documentation to kerneldoc comments, and add
> WARN_ON_ONCE asserts that the calling thread is a kernel thread and
> does not have ->mm set (or has ->mm set in the case of unuse_mm).
>
> Also give the functions a kthread_ prefix to better document the
> use case.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>


> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h |  4 +--
>  drivers/gpu/drm/i915/gvt/kvmgt.c           |  4 +--
>  drivers/usb/gadget/function/f_fs.c         |  4 +--
>  drivers/usb/gadget/legacy/inode.c          |  4 +--
>  drivers/vhost/vhost.c                      |  4 +--
>  fs/io-wq.c                                 |  6 ++--
>  fs/io_uring.c                              |  6 ++--
>  include/linux/kthread.h                    |  4 +--
>  kernel/kthread.c                           | 33 +++++++++++-----------
>  mm/oom_kill.c                              |  6 ++--
>  mm/vmacache.c                              |  4 +--
>  11 files changed, 39 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
> index bce5e93fefc8..63db84e09408 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
> @@ -192,9 +192,9 @@ uint8_t amdgpu_amdkfd_get_xgmi_hops_count(struct kgd_dev *dst, struct kgd_dev *s
>  			if ((mmptr) == current->mm) {			\
>  				valid = !get_user((dst), (wptr));	\
>  			} else if (current->flags & PF_KTHREAD) {	\
> -				use_mm(mmptr);				\
> +				kthread_use_mm(mmptr);			\
>  				valid = !get_user((dst), (wptr));	\
> -				unuse_mm(mmptr);			\
> +				kthread_unuse_mm(mmptr);		\
>  			}						\
>  			pagefault_enable();				\
>  		}							\
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index dee01c371bf5..92e9b340dbc2 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -2048,7 +2048,7 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa,
>  	if (kthread) {
>  		if (!mmget_not_zero(kvm->mm))
>  			return -EFAULT;
> -		use_mm(kvm->mm);
> +		kthread_use_mm(kvm->mm);
>  	}
>  
>  	idx = srcu_read_lock(&kvm->srcu);
> @@ -2057,7 +2057,7 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa,
>  	srcu_read_unlock(&kvm->srcu, idx);
>  
>  	if (kthread) {
> -		unuse_mm(kvm->mm);
> +		kthread_unuse_mm(kvm->mm);
>  		mmput(kvm->mm);
>  	}
>  
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index c57b1b2507c6..d9e48bd7c692 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -827,9 +827,9 @@ static void ffs_user_copy_worker(struct work_struct *work)
>  		mm_segment_t oldfs = get_fs();
>  
>  		set_fs(USER_DS);
> -		use_mm(io_data->mm);
> +		kthread_use_mm(io_data->mm);
>  		ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
> -		unuse_mm(io_data->mm);
> +		kthread_unuse_mm(io_data->mm);
>  		set_fs(oldfs);
>  	}
>  
> diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
> index 8b5233888bf8..a05552bc2ff8 100644
> --- a/drivers/usb/gadget/legacy/inode.c
> +++ b/drivers/usb/gadget/legacy/inode.c
> @@ -462,9 +462,9 @@ static void ep_user_copy_worker(struct work_struct *work)
>  	struct kiocb *iocb = priv->iocb;
>  	size_t ret;
>  
> -	use_mm(mm);
> +	kthread_use_mm(mm);
>  	ret = copy_to_iter(priv->buf, priv->actual, &priv->to);
> -	unuse_mm(mm);
> +	kthread_unuse_mm(mm);
>  	if (!ret)
>  		ret = -EFAULT;
>  
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 4e9ce54869af..1787d426a956 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -336,7 +336,7 @@ static int vhost_worker(void *data)
>  	mm_segment_t oldfs = get_fs();
>  
>  	set_fs(USER_DS);
> -	use_mm(dev->mm);
> +	kthread_use_mm(dev->mm);
>  
>  	for (;;) {
>  		/* mb paired w/ kthread_stop */
> @@ -364,7 +364,7 @@ static int vhost_worker(void *data)
>  				schedule();
>  		}
>  	}
> -	unuse_mm(dev->mm);
> +	kthread_unuse_mm(dev->mm);
>  	set_fs(oldfs);
>  	return 0;
>  }
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index c49c2bdbafb5..83c2868eff2a 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -169,7 +169,7 @@ static bool __io_worker_unuse(struct io_wqe *wqe, struct io_worker *worker)
>  		}
>  		__set_current_state(TASK_RUNNING);
>  		set_fs(KERNEL_DS);
> -		unuse_mm(worker->mm);
> +		kthread_unuse_mm(worker->mm);
>  		mmput(worker->mm);
>  		worker->mm = NULL;
>  	}
> @@ -416,7 +416,7 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe)
>  static void io_wq_switch_mm(struct io_worker *worker, struct io_wq_work *work)
>  {
>  	if (worker->mm) {
> -		unuse_mm(worker->mm);
> +		kthread_unuse_mm(worker->mm);
>  		mmput(worker->mm);
>  		worker->mm = NULL;
>  	}
> @@ -425,7 +425,7 @@ static void io_wq_switch_mm(struct io_worker *worker, struct io_wq_work *work)
>  		return;
>  	}
>  	if (mmget_not_zero(work->mm)) {
> -		use_mm(work->mm);
> +		kthread_use_mm(work->mm);
>  		if (!worker->mm)
>  			set_fs(USER_DS);
>  		worker->mm = work->mm;
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 27a4ecb724ca..367406381044 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5839,7 +5839,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
>  				err = -EFAULT;
>  				goto fail_req;
>  			}
> -			use_mm(ctx->sqo_mm);
> +			kthread_use_mm(ctx->sqo_mm);
>  			*mm = ctx->sqo_mm;
>  		}
>  
> @@ -5911,7 +5911,7 @@ static int io_sq_thread(void *data)
>  			 * may sleep.
>  			 */
>  			if (cur_mm) {
> -				unuse_mm(cur_mm);
> +				kthread_unuse_mm(cur_mm);
>  				mmput(cur_mm);
>  				cur_mm = NULL;
>  			}
> @@ -5987,7 +5987,7 @@ static int io_sq_thread(void *data)
>  
>  	set_fs(old_fs);
>  	if (cur_mm) {
> -		unuse_mm(cur_mm);
> +		kthread_unuse_mm(cur_mm);
>  		mmput(cur_mm);
>  	}
>  	revert_creds(old_cred);
> diff --git a/include/linux/kthread.h b/include/linux/kthread.h
> index c2d40c9672d6..12258ea077cf 100644
> --- a/include/linux/kthread.h
> +++ b/include/linux/kthread.h
> @@ -200,8 +200,8 @@ bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *work);
>  
>  void kthread_destroy_worker(struct kthread_worker *worker);
>  
> -void use_mm(struct mm_struct *mm);
> -void unuse_mm(struct mm_struct *mm);
> +void kthread_use_mm(struct mm_struct *mm);
> +void kthread_unuse_mm(struct mm_struct *mm);
>  
>  struct cgroup_subsys_state;
>  
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index ce4610316377..316db17f6b4f 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -1208,18 +1208,18 @@ void kthread_destroy_worker(struct kthread_worker *worker)
>  }
>  EXPORT_SYMBOL(kthread_destroy_worker);
>  
> -/*
> - * use_mm
> - *	Makes the calling kernel thread take on the specified
> - *	mm context.
> - *	(Note: this routine is intended to be called only
> - *	from a kernel thread context)
> +/**
> + * kthread_use_mm - make the calling kthread operate on an address space
> + * @mm: address space to operate on
>   */
> -void use_mm(struct mm_struct *mm)
> +void kthread_use_mm(struct mm_struct *mm)
>  {
>  	struct mm_struct *active_mm;
>  	struct task_struct *tsk = current;
>  
> +	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
> +	WARN_ON_ONCE(tsk->mm);
> +
>  	task_lock(tsk);
>  	active_mm = tsk->active_mm;
>  	if (active_mm != mm) {
> @@ -1236,20 +1236,19 @@ void use_mm(struct mm_struct *mm)
>  	if (active_mm != mm)
>  		mmdrop(active_mm);
>  }
> -EXPORT_SYMBOL_GPL(use_mm);
> +EXPORT_SYMBOL_GPL(kthread_use_mm);
>  
> -/*
> - * unuse_mm
> - *	Reverses the effect of use_mm, i.e. releases the
> - *	specified mm context which was earlier taken on
> - *	by the calling kernel thread
> - *	(Note: this routine is intended to be called only
> - *	from a kernel thread context)
> +/**
> + * kthread_use_mm - reverse the effect of kthread_use_mm()
> + * @mm: address space to operate on
>   */
> -void unuse_mm(struct mm_struct *mm)
> +void kthread_unuse_mm(struct mm_struct *mm)
>  {
>  	struct task_struct *tsk = current;
>  
> +	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
> +	WARN_ON_ONCE(!tsk->mm);
> +
>  	task_lock(tsk);
>  	sync_mm_rss(mm);
>  	tsk->mm = NULL;
> @@ -1257,7 +1256,7 @@ void unuse_mm(struct mm_struct *mm)
>  	enter_lazy_tlb(mm, tsk);
>  	task_unlock(tsk);
>  }
> -EXPORT_SYMBOL_GPL(unuse_mm);
> +EXPORT_SYMBOL_GPL(kthread_unuse_mm);
>  
>  #ifdef CONFIG_BLK_CGROUP
>  /**
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index dfc357614e56..958d2972313f 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -126,7 +126,7 @@ static bool oom_cpuset_eligible(struct task_struct *tsk, struct oom_control *oc)
>  
>  /*
>   * The process p may have detached its own ->mm while exiting or through
> - * use_mm(), but one or more of its subthreads may still have a valid
> + * kthread_use_mm(), but one or more of its subthreads may still have a valid
>   * pointer.  Return p, or any of its subthreads with a valid ->mm, with
>   * task_lock() held.
>   */
> @@ -919,8 +919,8 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
>  			continue;
>  		}
>  		/*
> -		 * No use_mm() user needs to read from the userspace so we are
> -		 * ok to reap it.
> +		 * No kthead_use_mm() user needs to read from the userspace so
> +		 * we are ok to reap it.
>  		 */
>  		if (unlikely(p->flags & PF_KTHREAD))
>  			continue;
> diff --git a/mm/vmacache.c b/mm/vmacache.c
> index cdc32a3b02fa..ceedbab82106 100644
> --- a/mm/vmacache.c
> +++ b/mm/vmacache.c
> @@ -25,8 +25,8 @@
>   * task's vmacache pertains to a different mm (ie, its own).  There is
>   * nothing we can do here.
>   *
> - * Also handle the case where a kernel thread has adopted this mm via use_mm().
> - * That kernel thread's vmacache is not applicable to this mm.
> + * Also handle the case where a kernel thread has adopted this mm via
> + * kthread_use_mm(). That kernel thread's vmacache is not applicable to this mm.
>   */
>  static inline bool vmacache_valid_mm(struct mm_struct *mm)
>  {