ACK/cmnt[X]: [X][X/linux-kvm][SRU][PATCH 1/1] mm: mlock: avoid increase mm->locked_vm on mlock() when already mlock2(, MLOCK_ONFAULT)

[Kleber Souza]

On 10/23/18 10:44, Po-Hsu Lin wrote:
> From: Simon Guo <wei.guo.simon at gmail.com>
>
> BugLink: https://bugs.launchpad.net/bugs/1793451
>
> When one vma was with flag VM_LOCKED|VM_LOCKONFAULT (by invoking
> mlock2(,MLOCK_ONFAULT)), it can again be populated with mlock() with
> VM_LOCKED flag only.
>
> There is a hole in mlock_fixup() which increase mm->locked_vm twice even
> the two operations are on the same vma and both with VM_LOCKED flags.
>
> The issue can be reproduced by following code:
>
>   mlock2(p, 1024 * 64, MLOCK_ONFAULT); //VM_LOCKED|VM_LOCKONFAULT
>   mlock(p, 1024 * 64);  //VM_LOCKED
>
> Then check the increase VmLck field in /proc/pid/status(to 128k).
>
> When vma is set with different vm_flags, and the new vm_flags is with
> VM_LOCKED, it is not necessarily be a "new locked" vma.  This patch
> corrects this bug by prevent mm->locked_vm from increment when old
> vm_flags is already VM_LOCKED.
>
> Link: http://lkml.kernel.org/r/1472554781-9835-3-git-send-email-wei.guo.simon@gmail.com
> Signed-off-by: Simon Guo <wei.guo.simon at gmail.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov at linux.intel.com>
> Cc: Alexey Klimov <klimov.linux at gmail.com>
> Cc: Eric B Munson <emunson at akamai.com>
> Cc: Geert Uytterhoeven <geert at linux-m68k.org>
> Cc: Mel Gorman <mgorman at techsingularity.net>
> Cc: Michal Hocko <mhocko at suse.com>
> Cc: Shuah Khan <shuah at kernel.org>
> Cc: Simon Guo <wei.guo.simon at gmail.com>
> Cc: Thierry Reding <treding at nvidia.com>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: David Rientjes <rientjes at google.com>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> (cherry picked from commit b155b4fde5bdde9fed439cd1f5ea07173df2ed31)
> Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>

As Stefan mentioned, no need to apply the patch to any 4.4 derivative
since they will get the patch after the rebase.

Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

> ---
>  mm/mlock.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 9d2e773..b03f160 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -504,6 +504,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
>  	int nr_pages;
>  	int ret = 0;
>  	int lock = !!(newflags & VM_LOCKED);
> +	vm_flags_t old_flags = vma->vm_flags;
>  
>  	if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
>  	    is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
> @@ -538,6 +539,8 @@ success:
>  	nr_pages = (end - start) >> PAGE_SHIFT;
>  	if (!lock)
>  		nr_pages = -nr_pages;
> +	else if (old_flags & VM_LOCKED)
> +		nr_pages = 0;
>  	mm->locked_vm += nr_pages;
>  
>  	/*