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SubjectRe: [patch] lockdep: annotate mm/slab.c

* Pekka Enberg <> wrote:

> Hi,
> On 7/13/06, Ingo Molnar <> wrote:
> >mm/slab.c uses nested locking when dealing with 'off-slab'
> >caches, in that case it allocates the slab header from the
> >(on-slab) kmalloc caches. Teach the lock validator about
> >this by putting all on-slab caches into a separate class.
> Which lock is that? This affects only caches that cache_grow() use, so
> we are really only interested in annotating kmalloc() on-slab caches
> (like in the patch), not _all_, right?

it's ->list_lock, and a sample nesting scenario is:

[<c013a9a8>] lock_acquire+0x78/0xa0
[<c0313e5a>] _spin_lock_nested+0x2a/0x40
[<c0163024>] __cache_free+0x484/0x5c0
[<c01632ad>] slab_destroy+0x14d/0x1e0
[<c0162ac9>] free_block+0x189/0x1e0
[<c01630f4>] __cache_free+0x554/0x5c0
[<c0163653>] kmem_cache_free+0x73/0xc0
[<c016a24f>] file_free_rcu+0xf/0x20
[<c0130755>] __rcu_process_callbacks+0x75/0x1b0
[<c0130bc7>] rcu_process_callbacks+0x27/0x50
[<c0123f3a>] tasklet_action+0x6a/0xf0
[<c012413b>] __do_softirq+0x8b/0x130
[<c0106ba3>] do_softirq+0x73/0x100

(the off-slab nesting is perfectly correct locking code AFAICS - it just
needs to be taught to lockdep - which the patch does. OTOH i'm less sure
about the NUMA alien-cache-draining nesting.)

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