Messages in this thread | | | Date | Mon, 29 Jun 2009 23:00:31 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC] fix RCU-callback-after-kmem_cache_destroy problem in sl[aou]b |
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On Mon, Jun 29, 2009 at 07:06:34PM -0500, Matt Mackall wrote: > On Mon, 2009-06-29 at 19:19 -0400, Christoph Lameter wrote: > > On Mon, 29 Jun 2009, Matt Mackall wrote: > > > > > This is a reasonable point, and in keeping with the design principle > > > 'callers should handle their own special cases'. However, I think it > > > would be more than a little surprising for kmem_cache_free() to do the > > > right thing, but not kmem_cache_destroy(). > > > > kmem_cache_free() must be used carefully when using SLAB_DESTROY_BY_RCU. > > The freed object can be accessed after free until the rcu interval > > expires (well sortof, it may even be reallocated within the interval). > > > > There are special RCU considerations coming already with the use of > > kmem_cache_free(). > > > > Adding RCU operations to the kmem_cache_destroy() logic may result in > > unnecessary RCU actions for slabs where the coder is ensuring that the > > RCU interval has passed by other means. > > Do we care? Cache destruction shouldn't be in anyone's fast path. > Correctness is more important and users are more liable to be correct > with this patch.
I am with Matt on this one -- if we are going to hand the users of SLAB_DESTROY_BY_RCU a hand grenade, let's at least leave the pin in.
Thanx, Paul
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