Re: [PATCH v3 5/7] proc/task_mmu: change proc_get_vma() to stop returning gate VMA at the end

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Thu, Sep 10, 2026 at 04:47:35PM -0700, Suren Baghdasaryan wrote:
> proc_get_vma() returning gate VMA at the end is desirable for the its
> current m_start/m_next callers, as they need to report a gate VMA at the
> end of the address space. This behavior is very specific to these callers
> and makes proc_get_vma() hard to use for other purposes.
>
> Move this usage-specific behavior into the callers themselves so that
> proc_get_vma() returns either a valid VMA, an error or a NULL when no
> more VMAs are available. This makes it more generic, simpler and usable
> in the later patches.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Yes, very good change, thanks!

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
>  fs/proc/task_mmu.c | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index ecce7ce116cb..9a3c996c1d61 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -236,9 +236,6 @@ static struct vm_area_struct *proc_get_vma(struct seq_file *m, loff_t *ppos)
>  		 * found the extended vma with the same vm_start.
>  		 */
>  		*ppos = vma->vm_end;
> -	} else {
> -		*ppos = SENTINEL_VMA_GATE;
> -		vma = get_gate_vma(priv->lock_ctx.mm);

Yeah this is just so confusing as-was.

>  	}
>
>  	return vma;
> @@ -248,6 +245,7 @@ static void *m_start(struct seq_file *m, loff_t *ppos)
>  {
>  	struct proc_maps_private *priv = m->private;
>  	struct proc_maps_locking_ctx *lock_ctx;
> +	struct vm_area_struct *vma;
>  	loff_t last_addr = *ppos;
>  	struct mm_struct *mm;
>
> @@ -280,16 +278,31 @@ static void *m_start(struct seq_file *m, loff_t *ppos)
>  	if (last_addr == SENTINEL_VMA_GATE)
>  		return get_gate_vma(mm);
>
> -	return proc_get_vma(m, ppos);
> +	vma = proc_get_vma(m, ppos);
> +	if (vma)
> +		return vma;
> +
> +	/* Return gate VMA at the end */
> +	*ppos = SENTINEL_VMA_GATE;
> +	return get_gate_vma(mm);
>  }
>
>  static void *m_next(struct seq_file *m, void *v, loff_t *ppos)
>  {
> +	struct proc_maps_private *priv = m->private;
> +	struct vm_area_struct *vma;
> +
>  	if (*ppos == SENTINEL_VMA_GATE) {
>  		*ppos = SENTINEL_VMA_END;
>  		return NULL;
>  	}
> -	return proc_get_vma(m, ppos);
> +	vma = proc_get_vma(m, ppos);
> +	if (vma)
> +		return vma;

OK so I guess the logic is, iterate through every VMA, then once you run out,
report the gate VMA. Makes sense.

> +
> +	/* Return gate VMA at the end */
> +	*ppos = SENTINEL_VMA_GATE;
> +	return get_gate_vma(priv->lock_ctx.mm);
>  }
>
>  static void m_stop(struct seq_file *m, void *v)
> --
> 2.55.0.1007.g17ff1f9808-goog
>

--
Cheers, Lorenzo