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authorLeon Yu <chianglungyu@gmail.com>2015-03-25 15:55:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-03-25 16:20:30 -0700
commit3fe89b3e2a7bbf3e97657104b9b33a9d81b950b3 (patch)
tree989d39235f82bdd65c0e621d844d3db41b0690ec /mm
parentdrivers/rtc/rtc-mrst: fix suspend/resume (diff)
downloadlinux-dev-3fe89b3e2a7bbf3e97657104b9b33a9d81b950b3.tar.xz
linux-dev-3fe89b3e2a7bbf3e97657104b9b33a9d81b950b3.zip
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 <chianglungyu@gmail.com> Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com> Reviewed-by: Michal Hocko <mhocko@suse.cz> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: David Rientjes <rientjes@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/mmap.c4
-rw-r--r--mm/rmap.c7
2 files changed, 8 insertions, 3 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index da9990acc08b..9ec50a368634 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -774,10 +774,8 @@ again: remove_next = 1 + (end > next->vm_end);
importer->anon_vma = exporter->anon_vma;
error = anon_vma_clone(importer, exporter);
- if (error) {
- importer->anon_vma = NULL;
+ if (error)
return error;
- }
}
}
diff --git a/mm/rmap.c b/mm/rmap.c
index 5e3e09081164..c161a14b6a8f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -287,6 +287,13 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
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;
}