Peter Zijlstra wrote:
On Tue, 2006-10-17 at 01:24 +1000, Nick Piggin wrote:
Also, the rest of the kernel tree (mainly uaccess and futexes) should be
converted ;)
Yeah, lotsa places to touch.
Index: linux-2.6/mm/filemap.h
===================================================================
--- linux-2.6.orig/mm/filemap.h 2006-10-14 20:20:20.000000000 +0200
+++ linux-2.6/mm/filemap.h 2006-10-15 17:17:45.000000000 +0200
@@ -21,6 +21,22 @@ __filemap_copy_from_user_iovec_inatomic(
size_t bytes);
/*
+ * By increasing the preempt_count we make sure the arch preempt
+ * handler bails out early, before taking any locks, so that the copy
+ * operation gets terminated early.
+ */
+pagefault_static inline void disable(void)
+{
+ inc_preempt_count();
I think we also need a barrier(); here. We need to make sure the preempt
count is written to memory before we hit the fault handler.
It will come from this thread, but I guess the fault is not an event the
compiler can forsee, so indeed it might optimise this into the wrong place.
Perhaps not with any copy*user implementation we have, but at least in
theory...
+pagefault_static inline void enable(void)
+{
+ dec_preempt_count();
+ preempt_check_resched();
+}
You'll want barriers before and after the dec_preempt_count, for similar
reasons.
--
SUSE Labs, Novell Inc.
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