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| author | Leon Yu <chianglungyu@gmail.com> | 2015-03-25 15:55:11 -0700 |
|---|---|---|
| committer | Zefan Li <lizefan@huawei.com> | 2015-04-14 17:34:04 +0800 |
| commit | 972dafe08e0434c3ce1caf5c86d7dae222d85588 (patch) | |
| tree | b3c82254bd23d17d28e3b5c0b25cd9be9f02be47 | |
| parent | 14b98571ea157c84211ffb38daee979b738856f1 (diff) | |
| download | lwn-972dafe08e0434c3ce1caf5c86d7dae222d85588.tar.gz lwn-972dafe08e0434c3ce1caf5c86d7dae222d85588.zip | |
mm: fix anon_vma->degree underflow in anon_vma endless growing prevention
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 <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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Zefan Li <lizefan@huawei.com>
| -rw-r--r-- | mm/mmap.c | 4 | ||||
| -rw-r--r-- | mm/rmap.c | 7 |
2 files changed, 8 insertions, 3 deletions
diff --git a/mm/mmap.c b/mm/mmap.c index f880ca164c00..208e70f1006d 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -571,10 +571,8 @@ 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 b7a64ec047a8..57f503b185a9 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -292,6 +292,13 @@ 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; } |