Hi Paul,
On 07/06/14 04:46, Paul E. McKenney wrote:
On Fri, May 30, 2014 at 11:29:41AM +1000, Greg Ungerer wrote:
On 29/05/14 23:11, One Thousand Gnomes wrote:
On Thu, 29 May 2014 12:08:32 +1000
Greg Ungerer <gerg@xxxxxxxxxxx> wrote:
Hi All,
Inside kernel/rcy/tree.c in __call_rcu() it does an alignment check on
the head pointer passed in. This trips on m68k systems, because they only
need alignment of 32bit quantities to 16bit boundaries.
__alignof perhaps ?
That might do. Change then becomes something like:
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2467,7 +2467,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_
unsigned long flags;
struct rcu_data *rdp;
- WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
+ WARN_ON_ONCE((unsigned long)head & (__alignof__(head) - 1)); /* Misaligned rcu_head! */
Hmmm... The purpose of the check is to reserve the low-order bits to
allow RCU to classify callbacks as being time-critical or not. RCU
can probably live with a single bit, but if there is some architecture
out there that simply refuses to do alignment, I need to know about it.
This change was prompted by this check tripping, so the alignment
issue is certainly real for m68k.
Regards
Greg
(See "git show 0bb7b59d6e2b8" for more info.)
So how about this instead?
- WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */
(Trying to remember if I have seen Linux kernel code that uses both
the lower bits...)
Thanx, Paul
if (debug_rcu_head_queue(head)) {
/* Probable double call_rcu(), so leak the callback. */
ACCESS_ONCE(head->func) = rcu_leak_callback;
Thanks
Greg
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