Re: [PATCH v2] mm/mremap: Don't account pages in vma_to_resize()

From: Brian Geffon
Date: Thu Jul 22 2021 - 12:01:20 EST

Whoops I missed that you did remove it from vma_to_resize() so then it
looks good to me.

Acked-By: Brian Geffon <bgeffon@xxxxxxxxxx>

On Thu, Jul 22, 2021 at 11:58 AM Brian Geffon <bgeffon@xxxxxxxxxx> wrote:
>
> On Wed, Jul 21, 2021 at 9:13 AM Dmitry Safonov <dima@xxxxxxxxxx> wrote:
> >
> > All this vm_unacct_memory(charged) dance seems to complicate the life
> > without a good reason. Furthermore, it seems not always done right on
> > error-pathes in mremap_to().
> > And worse than that: this `charged' difference is sometimes
> > double-accounted for growing MREMAP_DONTUNMAP mremap()s in move_vma():
> > : if (security_vm_enough_memory_mm(mm, new_len >> PAGE_SHIFT))
> >
> > Let's not do this.
> > Account memory in mremap() fast-path for growing VMAs or in move_vma()
> > for actually moving things. The same simpler way as it's done by
> > vm_stat_account(), but with a difference to call
> > security_vm_enough_memory_mm() before copying/adjusting VMA.
> >
> > Originally noticed by Chen Wandun:
> > https://lkml.kernel.org/r/20210717101942.120607-1-chenwandun@xxxxxxxxxx
> >
> > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> > Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Chen Wandun <chenwandun@xxxxxxxxxx>
> > Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> > Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> > Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > Cc: Minchan Kim <minchan@xxxxxxxxxx>
> > Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
> > Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> > Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > Cc: Wei Yongjun <weiyongjun1@xxxxxxxxxx>
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > Fixes: e346b3813067 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")
> > Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
> > ---
> > mm/mremap.c | 50 ++++++++++++++++++++++----------------------------
> > 1 file changed, 22 insertions(+), 28 deletions(-)
> >
> > diff --git a/mm/mremap.c b/mm/mremap.c
> > index 5989d3990020..b90c8e732e29 100644
> > --- a/mm/mremap.c
> > +++ b/mm/mremap.c
> > @@ -565,6 +565,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> > bool *locked, unsigned long flags,
> > struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
> > {
> > + long to_account = new_len - old_len;
> > struct mm_struct *mm = vma->vm_mm;
> > struct vm_area_struct *new_vma;
> > unsigned long vm_flags = vma->vm_flags;
> > @@ -583,6 +584,9 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> > if (mm->map_count >= sysctl_max_map_count - 3)
> > return -ENOMEM;
> >
> > + if (unlikely(flags & MREMAP_DONTUNMAP))
> > + to_account = new_len;
> > +
> > if (vma->vm_ops && vma->vm_ops->may_split) {
> > if (vma->vm_start != old_addr)
> > err = vma->vm_ops->may_split(vma, old_addr);
> > @@ -604,8 +608,8 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> > if (err)
> > return err;
> >
> > - if (unlikely(flags & MREMAP_DONTUNMAP && vm_flags & VM_ACCOUNT)) {
> > - if (security_vm_enough_memory_mm(mm, new_len >> PAGE_SHIFT))
> > + if (vm_flags & VM_ACCOUNT) {
> > + if (security_vm_enough_memory_mm(mm, to_account >> PAGE_SHIFT))
> > return -ENOMEM;
> > }
> >
> > @@ -613,8 +617,8 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> > new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
> > &need_rmap_locks);
> > if (!new_vma) {
> > - if (unlikely(flags & MREMAP_DONTUNMAP && vm_flags & VM_ACCOUNT))
> > - vm_unacct_memory(new_len >> PAGE_SHIFT);
> > + if (vm_flags & VM_ACCOUNT)
> > + vm_unacct_memory(to_account >> PAGE_SHIFT);
> > return -ENOMEM;
> > }
> >
> > @@ -708,8 +712,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> > }
> >
> > static struct vm_area_struct *vma_to_resize(unsigned long addr,
> > - unsigned long old_len, unsigned long new_len, unsigned long flags,
> > - unsigned long *p)
> > + unsigned long old_len, unsigned long new_len, unsigned long flags)
> > {
> > struct mm_struct *mm = current->mm;
> > struct vm_area_struct *vma;
> > @@ -768,13 +771,6 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
> > (new_len - old_len) >> PAGE_SHIFT))
> > return ERR_PTR(-ENOMEM);
> >
> > - if (vma->vm_flags & VM_ACCOUNT) {
> > - unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
> > - if (security_vm_enough_memory_mm(mm, charged))
> > - return ERR_PTR(-ENOMEM);
> > - *p = charged;
> > - }
> > -
> > return vma;
> > }
> >
> > @@ -787,7 +783,6 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> > struct mm_struct *mm = current->mm;
> > struct vm_area_struct *vma;
> > unsigned long ret = -EINVAL;
> > - unsigned long charged = 0;
> > unsigned long map_flags = 0;
> >
> > if (offset_in_page(new_addr))
> > @@ -830,7 +825,7 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> > old_len = new_len;
> > }
> >
> > - vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
> > + vma = vma_to_resize(addr, old_len, new_len, flags);
> > if (IS_ERR(vma)) {
> > ret = PTR_ERR(vma);
> > goto out;
> > @@ -853,7 +848,7 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> > ((addr - vma->vm_start) >> PAGE_SHIFT),
> > map_flags);
> > if (IS_ERR_VALUE(ret))
> > - goto out1;
> > + goto out;
> >
> > /* We got a new mapping */
> > if (!(flags & MREMAP_FIXED))
> > @@ -862,12 +857,6 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> > ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
> > uf_unmap);
> >
> > - if (!(offset_in_page(ret)))
> > - goto out;
> > -
> > -out1:
> > - vm_unacct_memory(charged);
> > -
> > out:
> > return ret;
> > }
> > @@ -899,7 +888,6 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> > struct mm_struct *mm = current->mm;
> > struct vm_area_struct *vma;
> > unsigned long ret = -EINVAL;
> > - unsigned long charged = 0;
> > bool locked = false;
> > bool downgraded = false;
> > struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
> > @@ -981,7 +969,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> > /*
> > * Ok, we need to grow..
> > */
> > - vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
> > + vma = vma_to_resize(addr, old_len, new_len, flags);
> > if (IS_ERR(vma)) {
> > ret = PTR_ERR(vma);
> > goto out;
> > @@ -992,10 +980,18 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> > if (old_len == vma->vm_end - addr) {
> > /* can we just expand the current mapping? */
> > if (vma_expandable(vma, new_len - old_len)) {
> > - int pages = (new_len - old_len) >> PAGE_SHIFT;
> > + long pages = (new_len - old_len) >> PAGE_SHIFT;
> > +
> > + if (vma->vm_flags & VM_ACCOUNT) {
> > + if (security_vm_enough_memory_mm(mm, pages)) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
> > + }
>
> Wasn't this whole check already performed in vma_to_resize()?
>
> >
> > if (vma_adjust(vma, vma->vm_start, addr + new_len,
> > vma->vm_pgoff, NULL)) {
> > + vm_unacct_memory(pages);
> > ret = -ENOMEM;
> > goto out;
> > }
> > @@ -1034,10 +1030,8 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> > &locked, flags, &uf, &uf_unmap);
> > }
> > out:
> > - if (offset_in_page(ret)) {
> > - vm_unacct_memory(charged);
> > + if (offset_in_page(ret))
> > locked = false;
> > - }
> > if (downgraded)
> > mmap_read_unlock(current->mm);
> > else
> > --
> > 2.32.0
> >