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authorHerbert Xu <herbert@gondor.apana.org.au>2005-10-16 23:29:20 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-17 11:59:10 -0400
commitb24d18aa743dad0c42918157c5d717686269d3a8 (patch)
treeceade1641a1806c5f3db2f4b344fe9070b488bad /Documentation/tipar.txt
parent3d80636a0d5f056ffc26472d05b6027a7a9f6e1c (diff)
[PATCH] list: add missing rcu_dereference on first element
It seems that all the list_*_rcu primitives are missing a memory barrier on the very first dereference. For example, #define list_for_each_rcu(pos, head) \ for (pos = (head)->next; prefetch(pos->next), pos != (head); \ pos = rcu_dereference(pos->next)) It will go something like: pos = (head)->next prefetch(pos->next) pos != (head) do stuff We're missing a barrier here. pos = rcu_dereference(pos->next) fetch pos->next barrier given by rcu_dereference(pos->next) store pos Without the missing barrier, the pos->next value may turn out to be stale. In fact, if "do stuff" were also dereferencing pos and relying on list_for_each_rcu to provide the barrier then it may also break. So here is a patch to make sure that we have a barrier for the first element in the list. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Acked-by: "Paul E. McKenney" <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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