Re: [PATCH v4 42/66] fs/proc/task_mmu: Stop using linked list and highest_vm_end

[Vlastimil Babka <vbabka@suse.cz>]

On 12/1/21 15:30, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
> 
> Remove references to mm_struct linked list and highest_vm_end for when
> they are removed
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> ---
>  fs/proc/internal.h |  2 +-
>  fs/proc/task_mmu.c | 73 ++++++++++++++++++++++++++--------------------
>  2 files changed, 42 insertions(+), 33 deletions(-)
> 
> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index 03415f3fb3a8..45b132c609ff 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -290,7 +290,7 @@ struct proc_maps_private {
>  	struct task_struct *task;
>  	struct mm_struct *mm;
>  #ifdef CONFIG_MMU
> -	struct vm_area_struct *tail_vma;
> +	struct vma_iterator iter;
>  #endif
>  #ifdef CONFIG_NUMA
>  	struct mempolicy *task_mempolicy;
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 300911d6575f..7cc97cdb88c2 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -122,12 +122,26 @@ static void release_task_mempolicy(struct proc_maps_private *priv)
>  }
>  #endif
>  
> +static struct vm_area_struct *proc_get_vma(struct proc_maps_private *priv,
> +						loff_t *ppos)
> +{
> +	struct vm_area_struct *vma = vma_next(&priv->iter);

This advances the iterator.

> +
> +	if (vma) {
> +		*ppos = vma->vm_start;

This advances *ppos.

> +	} else {
> +		*ppos = -2UL;
> +		vma = get_gate_vma(priv->mm);
> +	}
> +
> +	return vma;
> +}
> +
>  static void *m_start(struct seq_file *m, loff_t *ppos)
>  {
>  	struct proc_maps_private *priv = m->private;
>  	unsigned long last_addr = *ppos;
>  	struct mm_struct *mm;
> -	struct vm_area_struct *vma;
>  
>  	/* See m_next(). Zero at the start or after lseek. */
>  	if (last_addr == -1UL)
> @@ -151,31 +165,21 @@ static void *m_start(struct seq_file *m, loff_t *ppos)
>  		return ERR_PTR(-EINTR);
>  	}
>  
> +	vma_iter_init(&priv->iter, mm, last_addr);
>  	hold_task_mempolicy(priv);
> -	priv->tail_vma = get_gate_vma(mm);
> -
> -	vma = find_vma(mm, last_addr);
> -	if (vma)
> -		return vma;
> +	if (last_addr == -2UL)
> +		return get_gate_vma(mm);
>  
> -	return priv->tail_vma;
> +	return proc_get_vma(priv, ppos);

So here we advance those as part of m_start(), which I think is wrong in the
seqfile API. See seq_read_iter() in fs/seq_file.c how it handles a full
buffer, around the comment "// need a bigger buffer" it will do a stop() and
start() again and that's supposed to get the same vma.
seqfile is tricky, part #220121

>  }
>  
>  static void *m_next(struct seq_file *m, void *v, loff_t *ppos)
>  {
> -	struct proc_maps_private *priv = m->private;
> -	struct vm_area_struct *next, *vma = v;
> -
> -	if (vma == priv->tail_vma)
> -		next = NULL;
> -	else if (vma->vm_next)
> -		next = vma->vm_next;
> -	else
> -		next = priv->tail_vma;
> -
> -	*ppos = next ? next->vm_start : -1UL;
> -
> -	return next;
> +	if (*ppos == -2UL) {
> +		*ppos = -1UL;
> +		return NULL;
> +	}
> +	return proc_get_vma(m->private, ppos);
>  }
>  
>  static void m_stop(struct seq_file *m, void *v)
> @@ -843,16 +847,16 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
>  {
>  	struct proc_maps_private *priv = m->private;
>  	struct mem_size_stats mss;
> -	struct mm_struct *mm;
> +	struct mm_struct *mm = priv->mm;
>  	struct vm_area_struct *vma;
> -	unsigned long last_vma_end = 0;
> +	unsigned long vma_start = 0, last_vma_end = 0;
>  	int ret = 0;
> +	MA_STATE(mas, &mm->mm_mt, 0, 0);
>  
>  	priv->task = get_proc_task(priv->inode);
>  	if (!priv->task)
>  		return -ESRCH;
>  
> -	mm = priv->mm;
>  	if (!mm || !mmget_not_zero(mm)) {
>  		ret = -ESRCH;
>  		goto out_put_task;
> @@ -865,8 +869,13 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
>  		goto out_put_mm;
>  
>  	hold_task_mempolicy(priv);
> +	vma = mas_find(&mas, 0);
> +
> +	if (unlikely(!vma))
> +		goto empty_set;
>  
> -	for (vma = priv->mm->mmap; vma;) {
> +	vma_start = vma->vm_start;
> +	do {
>  		smap_gather_stats(vma, &mss, 0);
>  		last_vma_end = vma->vm_end;
>  
> @@ -875,6 +884,7 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
>  		 * access it for write request.
>  		 */
>  		if (mmap_lock_is_contended(mm)) {
> +			mas_pause(&mas);
>  			mmap_read_unlock(mm);
>  			ret = mmap_read_lock_killable(mm);
>  			if (ret) {
> @@ -918,7 +928,7 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
>  			 *    contains last_vma_end.
>  			 *    Iterate VMA' from last_vma_end.
>  			 */
> -			vma = find_vma(mm, last_vma_end - 1);
> +			vma = mas_find(&mas, ULONG_MAX);
>  			/* Case 3 above */
>  			if (!vma)
>  				break;
> @@ -932,11 +942,10 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
>  				smap_gather_stats(vma, &mss, last_vma_end);
>  		}
>  		/* Case 2 above */
> -		vma = vma->vm_next;
> -	}
> +	} while ((vma = mas_find(&mas, ULONG_MAX)) != NULL);
>  
> -	show_vma_header_prefix(m, priv->mm->mmap->vm_start,
> -			       last_vma_end, 0, 0, 0, 0);
> +empty_set:
> +	show_vma_header_prefix(m, vma_start, last_vma_end, 0, 0, 0, 0);
>  	seq_pad(m, ' ');
>  	seq_puts(m, "[rollup]\n");
>  
> @@ -1229,6 +1238,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
>  		return -ESRCH;
>  	mm = get_task_mm(task);
>  	if (mm) {
> +		MA_STATE(mas, &mm->mm_mt, 0, 0);
>  		struct mmu_notifier_range range;
>  		struct clear_refs_private cp = {
>  			.type = type,
> @@ -1248,7 +1258,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
>  		}
>  
>  		if (type == CLEAR_REFS_SOFT_DIRTY) {
> -			for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +			mas_for_each(&mas, vma, ULONG_MAX) {
>  				if (!(vma->vm_flags & VM_SOFTDIRTY))
>  					continue;
>  				vma->vm_flags &= ~VM_SOFTDIRTY;
> @@ -1260,8 +1270,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
>  						0, NULL, mm, 0, -1UL);
>  			mmu_notifier_invalidate_range_start(&range);
>  		}
> -		walk_page_range(mm, 0, mm->highest_vm_end, &clear_refs_walk_ops,
> -				&cp);
> +		walk_page_range(mm, 0, -1, &clear_refs_walk_ops, &cp);
>  		if (type == CLEAR_REFS_SOFT_DIRTY) {
>  			mmu_notifier_invalidate_range_end(&range);
>  			flush_tlb_mm(mm);