Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965588AbbDQNxo (ORCPT ); Fri, 17 Apr 2015 09:53:44 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:34136 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933691AbbDQNhZ (ORCPT ); Fri, 17 Apr 2015 09:37:25 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Leon Yu , Konstantin Khlebnikov , Michal Hocko , Rik van Riel , David Rientjes , Andrew Morton , Linus Torvalds Subject: [PATCH 3.19 043/101] mm: fix anon_vma->degree underflow in anon_vma endless growing prevention Date: Fri, 17 Apr 2015 15:28:31 +0200 Message-Id: <20150417132516.275823017@linuxfoundation.org> X-Mailer: git-send-email 2.3.5 In-Reply-To: <20150417132514.379828774@linuxfoundation.org> References: <20150417132514.379828774@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2870 Lines: 81 3.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Leon Yu commit 3fe89b3e2a7bbf3e97657104b9b33a9d81b950b3 upstream. I have constantly stumbled upon "kernel BUG at mm/rmap.c:399!" after upgrading to 3.19 and had no luck with 4.0-rc1 neither. So, after looking into new logic introduced by commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy"), I found chances are that unlink_anon_vmas() is called without incrementing dst->anon_vma->degree in anon_vma_clone() due to allocation failure. If dst->anon_vma is not NULL in error path, its degree will be incorrectly decremented in unlink_anon_vmas() and eventually underflow when exiting as a result of another call to unlink_anon_vmas(). That's how "kernel BUG at mm/rmap.c:399!" is triggered for me. This patch fixes the underflow by dropping dst->anon_vma when allocation fails. It's safe to do so regardless of original value of dst->anon_vma because dst->anon_vma doesn't have valid meaning if anon_vma_clone() fails. Besides, callers don't care dst->anon_vma in such case neither. Also suggested by Michal Hocko, we can clean up vma_adjust() a bit as anon_vma_clone() now does the work. [akpm@linux-foundation.org: tweak comment] Fixes: 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") Signed-off-by: Leon Yu Signed-off-by: Konstantin Khlebnikov Reviewed-by: Michal Hocko Acked-by: Rik van Riel Acked-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/mmap.c | 4 +--- mm/rmap.c | 7 +++++++ 2 files changed, 8 insertions(+), 3 deletions(-) --- a/mm/mmap.c +++ b/mm/mmap.c @@ -780,10 +780,8 @@ again: remove_next = 1 + (end > next-> importer->anon_vma = exporter->anon_vma; error = anon_vma_clone(importer, exporter); - if (error) { - importer->anon_vma = NULL; + if (error) return error; - } } } --- a/mm/rmap.c +++ b/mm/rmap.c @@ -287,6 +287,13 @@ int anon_vma_clone(struct vm_area_struct return 0; enomem_failure: + /* + * dst->anon_vma is dropped here otherwise its degree can be incorrectly + * decremented in unlink_anon_vmas(). + * We can safely do this because callers of anon_vma_clone() don't care + * about dst->anon_vma if anon_vma_clone() failed. + */ + dst->anon_vma = NULL; unlink_anon_vmas(dst); return -ENOMEM; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/