path: root/kernel/rcupdate.c
diff options
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-01-30 23:56:46 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-03-04 08:05:41 -0800
commite611eecd6f9f91d74beda8cfbb3b5e02abdeb5a1 (patch)
treee33c1874cf9cb737032a11985c537097625e28a1 /kernel/rcupdate.c
parentfe8e64071a4ff5925ced4f33cb32ba090a04649c (diff)
rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT.
The build will break if you change the Kconfig to allow DEBUG_OBJECTS_RCU_HEAD and !PREEMPT, so document the reasoning near where the breakage would occur. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcupdate.c')
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index afd21d17c081..f3240e987928 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -214,6 +214,11 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
* Ensure that queued callbacks are all executed.
* If we detect that we are nested in a RCU read-side critical
* section, we should simply fail, otherwise we would deadlock.
+ * Note that the machinery to reliably determine whether
+ * or not we are in an RCU read-side critical section
+ * exists only in the preemptible RCU implementations
+ * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why
+ * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT.
if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
irqs_disabled()) {