rcu: Make list_splice_init_rcu() account for RCU readers

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The list_splice_init_rcu() function allows a list visible to RCU readers
to be spliced into another list visible to RCU readers.  This is OK,
except for the use of INIT_LIST_HEAD(), which does pointer updates
without doing anything to make those updates safe for concurrent readers.

Of course, most of the time INIT_LIST_HEAD() is being used in reader-free
contexts, such as initialization or cleanup, so it is OK for it to update
pointers in an unsafe-for-RCU-readers manner.  This commit therefore
creates an INIT_LIST_HEAD_RCU() that uses ACCESS_ONCE() to make the updates
reader-safe.  The reason that we can use ACCESS_ONCE() instead of the more
typical rcu_assign_pointer() is that list_splice_init_rcu() is updating the
pointers to reference something that is already visible to readers, so
that there is no problem with pre-initialized values.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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This commit is contained in:

Paul E. McKenney 2013-08-23 09:40:42 -07:00

parent 829511d8aa

commit 2a855b644c

1 changed files with 21 additions and 2 deletions

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23

include/linux/rculist.h

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