linux-kernel - Re: [RFC PATCH RESEND 14/28] mm: mark VMAs as locked before isolating them

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Date:   Fri, 9 Sep 2022 15:35:27 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...e.de,
        dave@...olabs.net, willy@...radead.org, liam.howlett@...cle.com,
        peterz@...radead.org, laurent.dufour@...ibm.com,
        paulmck@...nel.org, luto@...nel.org, songliubraving@...com,
        peterx@...hat.com, david@...hat.com, dhowells@...hat.com,
        hughd@...gle.com, bigeasy@...utronix.de, kent.overstreet@...ux.dev,
        rientjes@...gle.com, axelrasmussen@...gle.com, joelaf@...gle.com,
        minchan@...gle.com, kernel-team@...roid.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH RESEND 14/28] mm: mark VMAs as locked before isolating
 them

Le 01/09/2022 à 19:35, Suren Baghdasaryan a écrit :
> Mark VMAs as locked before isolating them and clear their tree node so
> that isolated VMAs are easily identifiable. In the later patches page
> fault handlers will try locking the found VMA and will check whether
> the VMA was isolated. Locking VMAs before isolating them ensures that
> page fault handlers don't operate on isolated VMAs.

Found another place where the VMA should probably mark locked:
*** drivers/gpu/drm/drm_vma_manager.c:
drm_vma_node_revoke[338]       rb_erase(&entry->vm_rb, &node->vm_files);

There are 2 others entries in nommu.c but I guess this is not supported,
isn't it?


> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
>  mm/mmap.c  | 2 ++
>  mm/nommu.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 094678b4434b..b0d78bdc0de0 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -421,12 +421,14 @@ static inline void vma_rb_insert(struct vm_area_struct *vma,
>  
>  static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
>  {
> +	vma_mark_locked(vma);
>  	/*
>  	 * Note rb_erase_augmented is a fairly large inline function,
>  	 * so make sure we instantiate it only once with our desired
>  	 * augmented rbtree callbacks.
>  	 */
>  	rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
> +	RB_CLEAR_NODE(&vma->vm_rb);
>  }
>  
>  static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma,
> diff --git a/mm/nommu.c b/mm/nommu.c
> index e819cbc21b39..ff9933e57501 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -622,6 +622,7 @@ static void delete_vma_from_mm(struct vm_area_struct *vma)
>  	struct mm_struct *mm = vma->vm_mm;
>  	struct task_struct *curr = current;
>  
> +	vma_mark_locked(vma);
>  	mm->map_count--;
>  	for (i = 0; i < VMACACHE_SIZE; i++) {
>  		/* if the vma is cached, invalidate the entire cache */
> @@ -644,6 +645,7 @@ static void delete_vma_from_mm(struct vm_area_struct *vma)
>  
>  	/* remove from the MM's tree and list */
>  	rb_erase(&vma->vm_rb, &mm->mm_rb);
> +	RB_CLEAR_NODE(&vma->vm_rb);
>  
>  	__vma_unlink_list(mm, vma);
>  }