Messages in this thread Patch in this message | | | Date | Mon, 4 Aug 2008 19:57:30 +0200 | From | Andrea Arcangeli <> | Subject | [PATCH] workaround minor lockdep bug triggered by mm_take_all_locks |
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From: Andrea Arcangeli <andrea@qumranet.com>
Lockdep can't recognize if spinlocks are at a different address. So using trylock in a loop is one way to avoid lockdep to generate false positives. After lockdep will be fixed this change can and should be reverted.
Signed-off-by: Andrea Arcangeli <andrea@qumranet.com> ---
Resubmit because I didn't update the subject and so I improved the comments too. This is mostly to show it's a bug in lockdep and it can be trivially worked around without having to fix lockdep for real, any superior solution to this hack is more than welcome and recommended.
diff -r 3469dce61df1 mm/mmap.c --- a/mm/mmap.c Tue Jul 29 20:01:28 2008 +0200 +++ b/mm/mmap.c Mon Aug 04 19:54:27 2008 +0200 @@ -2279,8 +2279,12 @@ static void vm_lock_anon_vma(struct anon /* * The LSB of head.next can't change from under us * because we hold the mm_all_locks_mutex. + * + * spin_lock would confuse lockdep who doesn't notice + * the 'anon_vma' always changing address. */ - spin_lock(&anon_vma->lock); + while (!spin_trylock(&anon_vma->lock)) + cpu_relax(); /* * We can safely modify head.next after taking the * anon_vma->lock. If some other vma in this mm shares @@ -2310,7 +2314,12 @@ static void vm_lock_mapping(struct addre */ if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags)) BUG(); - spin_lock(&mapping->i_mmap_lock); + /* + * spin_lock would confuse lockdep who doesn't notice + * the 'mapping' always changing address. + */ + while (!spin_trylock(&mapping->i_mmap_lock)) + cpu_relax(); } }
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