Messages in this thread Patch in this message | | | Date | Mon, 4 Aug 2008 19:46:59 +0200 | From | Andrea Arcangeli <> | Subject | Re: [RFC][PATCH 7/7] lockdep: spin_lock_nest_lock() |
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From: Andrea Arcangeli <andrea@qumranet.com>
Lockdep can't recognize if spinlocks are at a different address. So trylock avoids 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> ---
On Mon, Aug 04, 2008 at 07:27:28PM +0200, Andrea Arcangeli wrote: > I can reproduce this now yes after a 'make sync'.
(btw it's not like I forgot to sync, but I sync against the wrong source tree previously because it was in the bash history, it's a bit complicate to explain)
> I assume it can't understand the spinlock address is different (I > think it uses the address as key only for static locks), so I wonder > if you could call print_deadlock_bug() from the failure path of the > spinlock to solve this?
In the meantime (as I doubt lockdep will get fixed any time soon) this will workaround it.
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 19:41:53 2008 +0200 @@ -2279,8 +2279,13 @@ 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 can't + * differentiate between the 'mapping' 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 +2315,13 @@ 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 can't + * differentiate between the 'mapping' always changing + * address. + */ + while (!spin_trylock(&mapping->i_mmap_lock)) + cpu_relax(); } }
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