Re: [PATCH v6 8/8] fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under per-vma locks

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

* Suren Baghdasaryan <surenb@google.com> [250704 02:07]:
> Utilize per-vma locks to stabilize vma after lookup without taking
> mmap_lock during PROCMAP_QUERY ioctl execution. While we might take
> mmap_lock for reading during contention, we do that momentarily only
> to lock the vma.
> This change is designed to reduce mmap_lock contention and prevent
> PROCMAP_QUERY ioctl calls from blocking address space updates.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
>  fs/proc/task_mmu.c | 60 ++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 48 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index ff3fe488ce51..0496d5969a51 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -487,28 +487,64 @@ static int pid_maps_open(struct inode *inode, struct file *file)
>  		PROCMAP_QUERY_VMA_FLAGS				\
>  )
>  
> -static int query_vma_setup(struct mm_struct *mm)
> +#ifdef CONFIG_PER_VMA_LOCK
> +
> +static int query_vma_setup(struct proc_maps_private *priv)
>  {
> -	return mmap_read_lock_killable(mm);
> +	priv->locked_vma = NULL;
> +	priv->mmap_locked = false;
> +
> +	return 0;
>  }
>  
> -static void query_vma_teardown(struct mm_struct *mm, struct vm_area_struct *vma)
> +static void query_vma_teardown(struct proc_maps_private *priv)
>  {
> -	mmap_read_unlock(mm);
> +	unlock_vma(priv);
> +}
> +
> +static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_private *priv,
> +						     unsigned long addr)
> +{
> +	struct vm_area_struct *vma;
> +
> +	rcu_read_lock();
> +	vma_iter_init(&priv->iter, priv->mm, addr);
> +	vma = get_next_vma(priv, addr);
> +	rcu_read_unlock();
> +
> +	return vma;
>  }
>  
> -static struct vm_area_struct *query_vma_find_by_addr(struct mm_struct *mm, unsigned long addr)
> +#else /* CONFIG_PER_VMA_LOCK */
> +
> +static int query_vma_setup(struct proc_maps_private *priv)
>  {
> -	return find_vma(mm, addr);
> +	return mmap_read_lock_killable(priv->mm);
>  }
>  
> -static struct vm_area_struct *query_matching_vma(struct mm_struct *mm,
> +static void query_vma_teardown(struct proc_maps_private *priv)
> +{
> +	mmap_read_unlock(priv->mm);
> +}
> +
> +static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_private *priv,
> +						     unsigned long addr)
> +{
> +	return find_vma(priv->mm, addr);
> +}
> +
> +#endif  /* CONFIG_PER_VMA_LOCK */
> +
> +static struct vm_area_struct *query_matching_vma(struct proc_maps_private *priv,
>  						 unsigned long addr, u32 flags)
>  {
>  	struct vm_area_struct *vma;
>  
>  next_vma:
> -	vma = query_vma_find_by_addr(mm, addr);
> +	vma = query_vma_find_by_addr(priv, addr);
> +	if (IS_ERR(vma))
> +		return vma;
> +
>  	if (!vma)
>  		goto no_vma;
>  
> @@ -584,13 +620,13 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
>  	if (!mm || !mmget_not_zero(mm))
>  		return -ESRCH;
>  
> -	err = query_vma_setup(mm);
> +	err = query_vma_setup(priv);
>  	if (err) {
>  		mmput(mm);
>  		return err;
>  	}
>  
> -	vma = query_matching_vma(mm, karg.query_addr, karg.query_flags);
> +	vma = query_matching_vma(priv, karg.query_addr, karg.query_flags);
>  	if (IS_ERR(vma)) {
>  		err = PTR_ERR(vma);
>  		vma = NULL;
> @@ -675,7 +711,7 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
>  	}
>  
>  	/* unlock vma or mmap_lock, and put mm_struct before copying data to user */
> -	query_vma_teardown(mm, vma);
> +	query_vma_teardown(priv);
>  	mmput(mm);
>  
>  	if (karg.vma_name_size && copy_to_user(u64_to_user_ptr(karg.vma_name_addr),
> @@ -695,7 +731,7 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
>  	return 0;
>  
>  out:
> -	query_vma_teardown(mm, vma);
> +	query_vma_teardown(priv);
>  	mmput(mm);
>  	kfree(name_buf);
>  	return err;
> -- 
> 2.50.0.727.gbf7dc18ff4-goog
>