Messages in this thread | | | Subject | Re: [PATCH] memcg: restore ss->id_lock to spinlock, using RCU for next | From | Eric Dumazet <> | Date | Thu, 19 Jan 2012 14:30:18 +0100 |
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Le jeudi 19 janvier 2012 à 04:28 -0800, Tejun Heo a écrit : > Hello, > > On Wed, Jan 18, 2012 at 11:33 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > > Interesting, but should be a patch on its own. > > Yeap, agreed. > > > Maybe other idr users can benefit from your idea as well, if patch is > > labeled "idr: allow idr_get_next() from rcu_read_lock" or something... > > > > I suggest introducing idr_get_next_rcu() helper to make the check about > > rcu cleaner. > > > > idr_get_next_rcu(...) > > { > > WARN_ON_ONCE(!rcu_read_lock_held()); > > return idr_get_next(...); > > } > > Hmmm... I don't know. Does having a separate set of interface help > much? It's easy to avoid/miss the test by using the other one. If we > really worry about it, maybe indicating which locking is to be used > during init is better? We can remember the lockdep map and trigger > WARN_ON_ONCE() if neither the lock or RCU read lock is held.
There is a rcu_dereference_raw(ptr) in idr_get_next()
This could be changed to rcu_dereference_check(ptr, condition) to get lockdep support for free :)
[ condition would be the appropriate lockdep_is_held(&the_lock_protecting_my_idr) or 'I use the rcu variant' and I hold rcu_read_lock ]
This would need to add a 'condition' parameter to idr_gen_next(), but we have very few users in kernel at this moment.
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