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net: explain netns notifiers a little better

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Eric explained this to me -- and afterwards the comment
made sense, but not before. Add the the critical point
about interfaces having to be gone from the netns before
subsys notifiers are called.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Johannes Berg 2009-07-15 06:16:34 +00:00 committed by David S. Miller
parent 27e0955184
commit 4edf547b4d
1 changed files with 9 additions and 7 deletions
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16
include/net/net_namespace.h
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@ -239,13 +239,15 @@ struct pernet_operations {
* needs per network namespace operations use device pernet operations,
* otherwise use pernet subsys operations.
*
* This is critically important. Most of the network code cleanup
* runs with the assumption that dev_remove_pack has been called so no
* new packets will arrive during and after the cleanup functions have
* been called. dev_remove_pack is not per namespace so instead the
* guarantee of no more packets arriving in a network namespace is
* provided by ensuring that all network devices and all sockets have
* left the network namespace before the cleanup methods are called.
* Network interfaces need to be removed from a dying netns _before_
* subsys notifiers can be called, as most of the network code cleanup
* (which is done from subsys notifiers) runs with the assumption that
* dev_remove_pack has been called so no new packets will arrive during
* and after the cleanup functions have been called. dev_remove_pack
* is not per namespace so instead the guarantee of no more packets
* arriving in a network namespace is provided by ensuring that all
* network devices and all sockets have left the network namespace
* before the cleanup methods are called.
*
* For the longest time the ipv4 icmp code was registered as a pernet
* device which caused kernel oops, and panics during network