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Re: [PATCH] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region

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On Tue, 17 Nov 2015 18:26:38 +0100 Piotr Kwapulinski <kwapulinski.piotr@gmail.com> wrote:

> The following flag comparison in mmap_region is not fully correct:
> 
> if (!(vm_flags & MAP_FIXED))
> 
> The vm_flags should not be compared with MAP_FIXED (0x10). It is a bit
> confusing. This condition is almost always true since VM_MAYREAD (0x10)
> flag is almost always set by default. This patch removes this condition.
> 
> ...
>
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1547,13 +1547,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>  	if (!may_expand_vm(mm, len >> PAGE_SHIFT)) {
>  		unsigned long nr_pages;
>  
> -		/*
> -		 * MAP_FIXED may remove pages of mappings that intersects with
> -		 * requested mapping. Account for the pages it would unmap.
> -		 */
> -		if (!(vm_flags & MAP_FIXED))
> -			return -ENOMEM;
> -
>  		nr_pages = count_vma_pages_range(mm, addr, addr + len);
>  
>  		if (!may_expand_vm(mm, (len >> PAGE_SHIFT) - nr_pages))

That looks simpler.

However the changelog doesn't describe the end-user visible effects of
the bug, as changelogs should always do.  Presumably this is causing
incorrect ENOMEM reporting due to RLIMIT_AS being exceeded, but this
isn't very specific.

So can you please fill in the details here?  Such info is needed when
deciding which kernel version(s) need the fix.

Thanks.
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[PATCH] mm: fix incorrect behavior when process virtual address space limit is exceeded Piotr Kwapulinski <kwapulinski.piotr@gmail.com> - 2015-11-16 18:40 +0100
  Re: [PATCH] mm: fix incorrect behavior when process virtual address  space limit is exceeded Michal Hocko <mhocko@kernel.org> - 2015-11-16 22:00 +0100
    Re: [PATCH] mm: fix incorrect behavior when process virtual address  space limit is exceeded Michal Hocko <mhocko@kernel.org> - 2015-11-17 01:40 +0100
    Re: [PATCH] mm: fix incorrect behavior when process virtual address  space limit is exceeded Cyril Hrubis <chrubis@suse.cz> - 2015-11-18 15:40 +0100
  Re: [PATCH] mm: fix incorrect behavior when process virtual  address space limit is exceeded Oleg Nesterov <oleg@redhat.com> - 2015-11-17 16:30 +0100
    Re: [PATCH] mm: fix incorrect behavior when process virtual  address space limit is exceeded Oleg Nesterov <oleg@redhat.com> - 2015-11-17 16:40 +0100
    [PATCH] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region Piotr Kwapulinski <kwapulinski.piotr@gmail.com> - 2015-11-17 18:30 +0100
      Re: [PATCH] mm/mmap.c: remove incorrect MAP_FIXED flag comparison  from mmap_region Andrew Morton <akpm@linux-foundation.org> - 2015-11-18 02:00 +0100
        Re: [PATCH] mm/mmap.c: remove incorrect MAP_FIXED flag comparison  from mmap_region Piotr Kwapulinski <kwapulinski.piotr@gmail.com> - 2015-11-18 17:30 +0100
          [PATCH v2 1/2] mm: fix incorrect behavior when process virtual address space limit is exceeded Piotr Kwapulinski <kwapulinski.piotr@gmail.com> - 2015-11-20 17:50 +0100
          [PATCH v2 2/2] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region Piotr Kwapulinski <kwapulinski.piotr@gmail.com> - 2015-11-20 17:50 +0100
            Re: [PATCH v2 2/2] mm/mmap.c: remove incorrect MAP_FIXED flag  comparison from mmap_region Michal Hocko <mhocko@kernel.org> - 2015-11-23 09:20 +0100
              [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region Piotr Kwapulinski <kwapulinski.piotr@gmail.com> - 2015-11-23 18:40 +0100
                Re: [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag  comparison from mmap_region Andrew Morton <akpm@linux-foundation.org> - 2015-11-23 23:20 +0100
                Re: [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag comparison  from mmap_region Piotr Kwapulinski <kwapulinski.piotr@gmail.com> - 2015-11-24 17:20 +0100
                Re: [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag  comparison from mmap_region Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2015-11-27 06:30 +0100
    Re: [PATCH] mm: fix incorrect behavior when process virtual address  space limit is exceeded Chris Metcalf <cmetcalf@ezchip.com> - 2015-11-17 18:40 +0100
      Re: [PATCH] mm: fix incorrect behavior when process virtual  address space limit is exceeded Oleg Nesterov <oleg@redhat.com> - 2015-11-17 19:10 +0100

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