Messages in this thread | | | Subject | Re: [PATCH] workaround minor lockdep bug triggered by mm_take_all_locks | From | Peter Zijlstra <> | Date | Mon, 04 Aug 2008 20:48:59 +0200 |
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On Mon, 2008-08-04 at 19:57 +0200, Andrea Arcangeli wrote: > 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>
NAK, come-on, you didn't even bother to look at the available annotations..
> --- > > 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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