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

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Message-ID: <CAJuCfpG+rzpEqDYAOr+CH-4remxJzuGKEH-=zpf_bWcah-1atw@mail.gmail.com>
Date: Wed, 9 Jul 2025 22:49:40 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: akpm@...ux-foundation.org, 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, 
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	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 Tue, Jul 8, 2025 at 10:37 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> 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?

Yes makes sense but let me do that outside of this patchset as it's
rather unrelated.

>
> >       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);
>