linux-kernel - Re: [PATCH v6 6/8] fs/proc/task_mmu: remove conversion of seq

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Message-ID: <0e0312c9-9a89-4a1b-a135-4425ea95d6f6@suse.cz>
Date: Tue, 8 Jul 2025 19:37:01 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, david@...hat.com,
 peterx@...hat.com, jannh@...gle.com, hannes@...xchg.org, mhocko@...nel.org,
 paulmck@...nel.org, shuah@...nel.org, adobriyan@...il.com,
 brauner@...nel.org, josef@...icpanda.com, yebin10@...wei.com,
 linux@...ssschuh.net, willy@...radead.org, osalvador@...e.de,
 andrii@...nel.org, ryan.roberts@....com, christophe.leroy@...roup.eu,
 tjmercier@...gle.com, kaleshsingh@...gle.com, aha310510@...il.com,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v6 6/8] fs/proc/task_mmu: remove conversion of seq_file
 position to unsigned

On 7/4/25 08:07, Suren Baghdasaryan wrote:
> Back in 2.6 era, last_addr used to be stored in seq_file->version
> variable, which was unsigned long. As a result, sentinels to represent
> gate vma and end of all vmas used unsigned values. In more recent
> kernels we don't used seq_file->version anymore and therefore conversion
> from loff_t into unsigned type is not needed. Similarly, sentinel values
> don't need to be unsigned. Remove type conversion for set_file position
> and change sentinel values to signed.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Some stuff in the code gave me a pause but it's out of scope here so just in
case someone wants to do some extra churn...

> ---
>  fs/proc/task_mmu.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 751479eb128f..b8bc06d05a72 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -135,7 +135,7 @@ static struct vm_area_struct *proc_get_vma(struct proc_maps_private *priv,
>  	if (vma) {
>  		*ppos = vma->vm_start;
>  	} else {
> -		*ppos = -2UL;
> +		*ppos = -2;
>  		vma = get_gate_vma(priv->mm);
>  	}
>  
> @@ -145,11 +145,11 @@ static struct vm_area_struct *proc_get_vma(struct proc_maps_private *priv,
>  static void *m_start(struct seq_file *m, loff_t *ppos)
>  {
>  	struct proc_maps_private *priv = m->private;
> -	unsigned long last_addr = *ppos;
> +	loff_t last_addr = *ppos;
>  	struct mm_struct *mm;
>  
>  	/* See m_next(). Zero at the start or after lseek. */
> -	if (last_addr == -1UL)
> +	if (last_addr == -1)
>  		return NULL;
>  
>  	priv->task = get_proc_task(priv->inode);
> @@ -170,9 +170,9 @@ static void *m_start(struct seq_file *m, loff_t *ppos)
>  		return ERR_PTR(-EINTR);
>  	}
>  
> -	vma_iter_init(&priv->iter, mm, last_addr);
> +	vma_iter_init(&priv->iter, mm, (unsigned long)last_addr);

I wonder if this should rather be done only after dealing with the -2 case
below. It seems wrong to init the iterator with a bogus address. What if it
acquires some sanity checks?

>  	hold_task_mempolicy(priv);

It seems suboptimal to do that mempolicy refcount dance for numa_maps sake
even if we're reading a different /proc file... maybe priv could have a flag
to determine?

> -	if (last_addr == -2UL)
> +	if (last_addr == -2)
>  		return get_gate_vma(mm);

I think only after the above it makes sense to init the iterator?

>  	return proc_get_vma(priv, ppos);
> @@ -180,8 +180,8 @@ static void *m_start(struct seq_file *m, loff_t *ppos)
>  
>  static void *m_next(struct seq_file *m, void *v, loff_t *ppos)
>  {
> -	if (*ppos == -2UL) {
> -		*ppos = -1UL;
> +	if (*ppos == -2) {
> +		*ppos = -1;
>  		return NULL;
>  	}
>  	return proc_get_vma(m->private, ppos);