Herbert Xu b24d18aa74
[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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b24d18aa74