From b800c91a0517071156e772d4fb329ad33590da62 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Sun, 11 Jan 2015 16:54:06 +0300 Subject: [PATCH] mm: fix corner case in anon_vma endless growing prevention Fix for BUG_ON(anon_vma->degree) splashes in unlink_anon_vmas() ("kernel BUG at mm/rmap.c:399!") caused by commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") 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 Reported-and-tested-by: Chris Clayton Reported-and-tested-by: Oded Gabbay Reported-and-tested-by: Chih-Wei Huang Acked-by: Rik van Riel Acked-by: Vlastimil Babka Cc: Daniel Forrest Cc: Michal Hocko Cc: stable@vger.kernel.org # to match back-porting of 7a3ef208e662 Signed-off-by: Linus Torvalds --- Reading git-format-patch failed