Re: [PATCH] mm: fix corner case in anon_vma endless growing prevention

[Rik van Riel]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 01/11/2015 08:54 AM, Konstantin Khlebnikov wrote:
> Fix for BUG_ON(anon_vma->degree) splashes in unlink_anon_vmas() 
> ("kernel BUG at mm/rmap.c:399!").
> 
> Anon_vma_clone() is usually called for a copy of source vma in
> destination argument. If source vma has anon_vma it should be
> already in dst->anon_vma. NULL in dst->anon_vma is used as a sign
> that it's called from anon_vma_fork(). In this case
> anon_vma_clone() finds anon_vma for reusing.
> 
> Vma_adjust() calls it differently and this breaks anon_vma reusing
> logic: anon_vma_clone() links vma to old anon_vma and updates
> degree counters but vma_adjust() overrides vma->anon_vma right
> after that. As a result final unlink_anon_vmas() decrements degree
> for wrong anon_vma.
> 
> This patch assigns ->anon_vma before calling anon_vma_clone().
> 
> Signed-off-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx> Fixes:
> 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") 
> Tested-by: Chris Clayton <chris2553@xxxxxxxxxxxxxx> Tested-by: Oded
> Gabbay <oded.gabbay@xxxxxxx> Cc: Daniel Forrest
> <dan.forrest@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxx> Cc:
> Rik van Riel <riel@xxxxxxxxxx>

Acked-by: Rik van Riel <riel@xxxxxxxxxx>

- -- 
All rights reversed
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEcBAEBAgAGBQJUsoe+AAoJEM553pKExN6D4x0H/RpBJella2+JhOBPyCBtLY7Z
9w8n14TlqEq7cK/WRmjhYZfVMNGIG3MDe+nAH0hTF0teh/MvJuAkraYnPxtIZYqX
R7IpNOUS3HJBLqsRjNdVNsoMnWOGBC6j/RV70pLj1VklZnq/VDsUPybm0XWk1oh6
nC1QhdLfcnuaFS4M1lzsSyURwQYxi+2vv/kFdtYscArTYmjI7I4gCP3fD7lQKCwK
za0z/oZb5Z5cOHXyQfe/HUROCCNUZUQfcX1XvW+TWvuwcatOvKeVCmJAy5/aPkfH
THtwAP6EyZpu5XwsYXCNfbyalqYpH5lKxd5C+vG86YKEYZyeqRLKLeYAVY3yTho=
=v95A
-----END PGP SIGNATURE-----
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/