Re: [RFC 1/2] [RFC] mm: Account anon mappings as RLIMIT_DATA

[Konstantin Khlebnikov]

On Sun, Dec 13, 2015 at 11:14 PM, Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote:
> When inspecting a vague code inside prctl(PR_SET_MM_MEM)
> call (which testing the RLIMIT_DATA value to figure out
> if we're allowed to assign new @start_brk, @brk, @start_data,
> @end_data from mm_struct) it's been commited that RLIMIT_DATA
> in a form it's implemented now doesn't do anything useful
> because most of user-space libraries use mmap() syscall
> for dynamic memory allocations.
>
> So Linus suggested to convert RLIMIT_DATA rlimit into something
> suitable for anonymous memory accounting. Here we introduce
> new @anon_vm member into mm descriptor which is updated
> on every vm_stat_account() call.

I dont like this part. VmData already here but  you add new VmAnon
which has even more vague meaning. And after that RLIMIT_DATA limits
VmAnon not VmData.

I have alternative solution. have a look. (patch follows)

>
> Tests for RLIMIT_DATA are done in three places:
>  - mmap_region: when user calls mmap() helper
>  - do_brk: for brk() helper
>  - vma_to_resize: when mremap() is used
>
> The do_brk() is also used in vm_brk() which is called
> when the kernel loads Elf and aout files to execute.
>
> Because test for limit is done in do_brk helper we
> no longer need to call check_data_rlimit here.
>
> v2:
>  - update doc
>  - add may_expand_anon_vm helper
>  - call for RLIMIT_DATA test in mremap and do_brk
>
> CC: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
> CC: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> CC: Willy Tarreau <w@xxxxxx>
> CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> CC: Kees Cook <keescook@xxxxxxxxxx>
> CC: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
> CC: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
> CC: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> CC: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
> CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> ---
>  Documentation/filesystems/proc.txt |    1
>  fs/proc/task_mmu.c                 |    2 +
>  include/linux/mm_types.h           |    1
>  mm/mmap.c                          |   46 ++++++++++++++++++++++---------------
>  mm/mremap.c                        |    5 ++++
>  5 files changed, 37 insertions(+), 18 deletions(-)
>
> Index: linux-ml.git/Documentation/filesystems/proc.txt
> ===================================================================
> --- linux-ml.git.orig/Documentation/filesystems/proc.txt
> +++ linux-ml.git/Documentation/filesystems/proc.txt
> @@ -233,6 +233,7 @@ Table 1-2: Contents of the status files
>   VmHWM                       peak resident set size ("high water mark")
>   VmRSS                       size of memory portions
>   VmData                      size of data, stack, and text segments
> + VmAnon                      size of anonymous private memory (not file backended)
>   VmStk                       size of data, stack, and text segments
>   VmExe                       size of text segment
>   VmLib                       size of shared library code
> Index: linux-ml.git/fs/proc/task_mmu.c
> ===================================================================
> --- linux-ml.git.orig/fs/proc/task_mmu.c
> +++ linux-ml.git/fs/proc/task_mmu.c
> @@ -53,6 +53,7 @@ void task_mem(struct seq_file *m, struct
>                 "VmHWM:\t%8lu kB\n"
>                 "VmRSS:\t%8lu kB\n"
>                 "VmData:\t%8lu kB\n"
> +               "VmAnon:\t%8lu kB\n"
>                 "VmStk:\t%8lu kB\n"
>                 "VmExe:\t%8lu kB\n"
>                 "VmLib:\t%8lu kB\n"
> @@ -66,6 +67,7 @@ void task_mem(struct seq_file *m, struct
>                 hiwater_rss << (PAGE_SHIFT-10),
>                 total_rss << (PAGE_SHIFT-10),
>                 data << (PAGE_SHIFT-10),
> +               mm->anon_vm << (PAGE_SHIFT-10),
>                 mm->stack_vm << (PAGE_SHIFT-10), text, lib,
>                 ptes >> 10,
>                 pmds >> 10,
> Index: linux-ml.git/include/linux/mm_types.h
> ===================================================================
> --- linux-ml.git.orig/include/linux/mm_types.h
> +++ linux-ml.git/include/linux/mm_types.h
> @@ -429,6 +429,7 @@ struct mm_struct {
>         unsigned long shared_vm;        /* Shared pages (files) */
>         unsigned long exec_vm;          /* VM_EXEC & ~VM_WRITE */
>         unsigned long stack_vm;         /* VM_GROWSUP/DOWN */
> +       unsigned long anon_vm;          /* Anonymous pages mapped */
>         unsigned long def_flags;
>         unsigned long start_code, end_code, start_data, end_data;
>         unsigned long start_brk, brk, start_stack;
> Index: linux-ml.git/mm/mmap.c
> ===================================================================
> --- linux-ml.git.orig/mm/mmap.c
> +++ linux-ml.git/mm/mmap.c
> @@ -309,16 +309,6 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
>         if (brk < min_brk)
>                 goto out;
>
> -       /*
> -        * Check against rlimit here. If this check is done later after the test
> -        * of oldbrk with newbrk then it can escape the test and let the data
> -        * segment grow beyond its set limit the in case where the limit is
> -        * not page aligned -Ram Gupta
> -        */
> -       if (check_data_rlimit(rlimit(RLIMIT_DATA), brk, mm->start_brk,
> -                             mm->end_data, mm->start_data))
> -               goto out;
> -
>         newbrk = PAGE_ALIGN(brk);
>         oldbrk = PAGE_ALIGN(mm->brk);
>         if (oldbrk == newbrk)
> @@ -1223,6 +1213,9 @@ void vm_stat_account(struct mm_struct *m
>                         mm->exec_vm += pages;
>         } else if (flags & stack_flags)
>                 mm->stack_vm += pages;
> +
> +       if (anon_accountable_mapping(file, flags))
> +               mm->anon_vm += pages;
>  }
>  #endif /* CONFIG_PROC_FS */
>
> @@ -1578,6 +1571,14 @@ unsigned long mmap_region(struct file *f
>         }
>
>         /*
> +        * For anon mappings make sure we don't exceed the limit.
> +        */
> +       if (anon_accountable_mapping(file, vm_flags)) {
> +               if (!may_expand_anon_vm(mm, len >> PAGE_SHIFT))
> +                       return -ENOMEM;
> +       }
> +
> +       /*
>          * Can we just expand an old mapping?
>          */
>         vma = vma_merge(mm, prev, addr, addr + len, vm_flags,
> @@ -2760,7 +2761,8 @@ static unsigned long do_brk(unsigned lon
>         }
>
>         /* Check against address space limits *after* clearing old maps... */
> -       if (!may_expand_vm(mm, len >> PAGE_SHIFT))
> +       if (!may_expand_vm(mm, len >> PAGE_SHIFT) ||
> +           !may_expand_anon_vm(mm, len >> PAGE_SHIFT))
>                 return -ENOMEM;
>
>         if (mm->map_count > sysctl_max_map_count)
> @@ -2795,6 +2797,7 @@ static unsigned long do_brk(unsigned lon
>  out:
>         perf_event_mmap(vma);
>         mm->total_vm += len >> PAGE_SHIFT;
> +       mm->anon_vm += len >> PAGE_SHIFT;
>         if (flags & VM_LOCKED)
>                 mm->locked_vm += (len >> PAGE_SHIFT);
>         vma->vm_flags |= VM_SOFTDIRTY;
> @@ -2982,20 +2985,27 @@ out:
>         return NULL;
>  }
>
> +static inline int __may_expand_vm(unsigned int limit,
> +                                 unsigned long cur,
> +                                 unsigned long npages)
> +{
> +       unsigned long lim = rlimit(limit) >> PAGE_SHIFT;
> +
> +       return ((cur + npages) > lim) ? 0 : 1;
> +}
> +
>  /*
>   * Return true if the calling process may expand its vm space by the passed
>   * number of pages
>   */
>  int may_expand_vm(struct mm_struct *mm, unsigned long npages)
>  {
> -       unsigned long cur = mm->total_vm;       /* pages */
> -       unsigned long lim;
> -
> -       lim = rlimit(RLIMIT_AS) >> PAGE_SHIFT;
> +       return __may_expand_vm(RLIMIT_AS, mm->total_vm, npages);
> +}
>
> -       if (cur + npages > lim)
> -               return 0;
> -       return 1;
> +int may_expand_anon_vm(struct mm_struct *mm, unsigned long npages)
> +{
> +       return __may_expand_vm(RLIMIT_DATA, mm->anon_vm, npages);
>  }
>
>  static int special_mapping_fault(struct vm_area_struct *vma,
> Index: linux-ml.git/mm/mremap.c
> ===================================================================
> --- linux-ml.git.orig/mm/mremap.c
> +++ linux-ml.git/mm/mremap.c
> @@ -382,6 +382,11 @@ static struct vm_area_struct *vma_to_res
>         if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
>                 return ERR_PTR(-ENOMEM);
>
> +       if (anon_accountable_mapping(vma->vm_file, vma->vm_flags)) {
> +               if (!may_expand_anon_vm(mm, (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))
>
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