From: Eric Dumazet Date: Mon, 13 Sep 2010 12:24:54 +0000 (+0000) Subject: net: use rcu_barrier() in rollback_registered_many X-Git-Tag: v2.6.36-rc5~12^2~14 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ef885afbf8a37689afc1d9d545e2f3e7a8276c17;p=pandora-kernel.git net: use rcu_barrier() in rollback_registered_many netdev_wait_allrefs() waits that all references to a device vanishes. It currently uses a _very_ pessimistic 250 ms delay between each probe. Some users reported that no more than 4 devices can be dismantled per second, this is a pretty serious problem for some setups. Most of the time, a refcount is about to be released by an RCU callback, that is still in flight because rollback_registered_many() uses a synchronize_rcu() call instead of rcu_barrier(). Problem is visible if number of online cpus is one, because synchronize_rcu() is then a no op. time to remove 50 ipip tunnels on a UP machine : before patch : real 11.910s after patch : real 1.250s Reported-by: Nicolas Dichtel Reported-by: Octavian Purdila Reported-by: Benjamin LaHaise Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- Reading git-diff-tree failed