Re: [PATCH 0/1] mm/hugetlb: fix huge page reservation leak in private mapping error paths

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> From: "Mike Kravetz" <mike.kravetz@oracle.com>
> To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
> Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>, "Naoya Horiguchi" <n-horiguchi@ah.jp.nec.com>, "Michal
> Hocko" <mhocko@suse.com>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, "Hillf Danton"
> <hillf.zj@alibaba-inc.com>, "Dave Hansen" <dave.hansen@linux.intel.com>, "Jan Stancek" <jstancek@redhat.com>, "Mike
> Kravetz" <mike.kravetz@oracle.com>
> Sent: Thursday, 20 October, 2016 5:11:16 AM
> Subject: [PATCH 0/1] mm/hugetlb: fix huge page reservation leak in private mapping error paths
> 
> This issue was discovered by Jan Stancek as described in
> https://lkml.kernel.org/r/57FF7BB4.1070202@redhat.com
> 
> Error paths in hugetlb_cow() and hugetlb_no_page() do not properly clean
> up reservation entries when freeing a newly allocated huge page.  This
> issue was introduced with commit 67961f9db8c4 ("mm/hugetlb: fix huge page
> reserve accounting for private mappings).  That commit uses the information
> in private mapping reserve maps to determine if a reservation was already
> consumed.  This is important in the case of hole punch and truncate as the
> pages are released, but reservation entries are not restored.
> 
> This patch restores the reserve entries in hugetlb_cow and hugetlb_no_page
> such that reserve entries are consistent with the global reservation count.
> 
> The huge page reservation code is quite hard to follow, and this patch
> makes it even more complex.  One thought I had was to change the way
> hole punch and truncate work so that private mapping pages are not thrown
> away.  This would eliminate the need for this patch as well as 67961f9db8c4.
> It would change the existing semantics (as seen by the user) in this area,
> but I believe the documentation (man pages) say the behavior is unspecified.
> This could be a future change as well as rewriting the existing reservation
> code to make it easier to understand/maintain.  Thoughts?
> 
> In any case, this patch addresses the immediate issue.

Mike,

Just to confirm, I ran this patch on my setup (without the patch from Aneesh)
with libhugetlbfs testsuite in loop for several hours. There were no
ENOMEM/OOM failures, I did not observe resv leak after it finished.

Regards,
Jan

> 
> Mike Kravetz (1):
>   mm/hugetlb: fix huge page reservation leak in private mapping error
>     paths
> 
>  mm/hugetlb.c | 66
>  ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 66 insertions(+)
> 
> --
> 2.7.4
> 
> 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>