Re: [PATCH v4 42/66] fs/proc/task_mmu: Stop using linked list and highest_vm_end
From: Vlastimil Babka
Date: Fri Jan 21 2022 - 06:53:09 EST
On 12/1/21 15:30, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
>
> Remove references to mm_struct linked list and highest_vm_end for when
> they are removed
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> 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);