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  1. 17 10月, 2005 2 次提交
    • H
      [PATCH] list: add missing rcu_dereference on first element · b24d18aa
      由 Herbert Xu 提交于 
      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: NHerbert Xu <herbert@gondor.apana.org.au>
Acked-by: N"Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      b24d18aa
    • L
      Fix memory ordering bug in page reclaim · 3d80636a
      由 Linus Torvalds 提交于 
      As noticed by Nick Piggin, we need to make sure that we check the page
count before we check for PageDirty, since the dirty check is only valid
if the count implies that we're the only possible ones holding the page.

We always did do this, but the code needs a read-memory-barrier to make
sure that the orderign is also honored by the CPU.

(The writer side is ordered due to the atomic decrement and test on the
page count, see the discussion on linux-kernel)
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      3d80636a
  3. 16 10月, 2005 2 次提交
  5. 15 10月, 2005 21 次提交
  7. 14 10月, 2005 15 次提交