rcu: Tighten up __call_rcu() rcu_head alignment check

Commit 720abae3d68ae ("rcu: force alignment on struct
callback_head/rcu_head") forced the rcu_head (AKA callback_head)
structure's alignment to pointer size, that is, to 4-byte boundaries on
32-bit systems and to 8-byte boundaries on 64-bit systems.  This
commit therefore checks for this same alignment in __call_rcu(),
which used to contain a looser check for two-byte alignment.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 69a5611a7e7c03dcf950d94badfcce3445863440..37e4f7d2be0c85ba34174678a371cbce4073ef51 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3121,7 +3121,9 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func,
        unsigned long flags;
        struct rcu_data *rdp;
 
-       WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */
+       /* Misaligned rcu_head! */
+       WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
+
        if (debug_rcu_head_queue(head)) {
                /* Probable double call_rcu(), so leak the callback. */
                WRITE_ONCE(head->func, rcu_leak_callback);