From 3fe89b3e2a7bbf3e97657104b9b33a9d81b950b3 Mon Sep 17 00:00:00 2001 From: Leon Yu Date: Wed, 25 Mar 2015 15:55:11 -0700 Subject: [PATCH] mm: fix anon_vma->degree underflow in anon_vma endless growing prevention 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 Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-format-patch failed