summaryrefslogtreecommitdiff
path: root/include/linux/rcupdate.h
diff options
context:
space:
mode:
authorSteven Rostedt (VMware) <rostedt@goodmis.org>2017-04-07 12:20:36 -0400
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2017-04-10 15:22:03 -0400
commit03ecd3f48e57f2e6154584e0ee7450d7a05e2d3b (patch)
tree706b326ec25b81eab47468664f299de274ca9ba3 /include/linux/rcupdate.h
parenta278d4718988a253a08d12e6d76c80979693d39e (diff)
rcu/tracing: Add rcu_disabled to denote when rcu_irq_enter() will not work
Tracing uses rcu_irq_enter() as a way to make sure that RCU is watching when it needs to use rcu_read_lock() and friends. This is because tracing can happen as RCU is about to enter user space, or about to go idle, and RCU does not watch for RCU read side critical sections as it makes the transition. There is a small location within the RCU infrastructure that rcu_irq_enter() itself will not work. If tracing were to occur in that section it will break if it tries to use rcu_irq_enter(). Originally, this happens with the stack_tracer, because it will call save_stack_trace when it encounters stack usage that is greater than any stack usage it had encountered previously. There was a case where that happened in the RCU section where rcu_irq_enter() did not work, and lockdep complained loudly about it. To fix it, stack tracing added a call to be disabled and RCU would disable stack tracing during the critical section that rcu_irq_enter() was inoperable. This solution worked, but there are other cases that use rcu_irq_enter() and it would be a good idea to let RCU give a way to let others know that rcu_irq_enter() will not work. For example, in trace events. Another helpful aspect of this change is that it also moves the per cpu variable called in the RCU critical section into a cache locale along with other RCU per cpu variables used in that same location. I'm keeping the stack_trace_disable() code, as that still could be used in the future by places that really need to disable it. And since it's only a static inline, it wont take up any kernel text if it is not used. Link: http://lkml.kernel.org/r/20170405093207.404f8deb@gandalf.local.home Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'include/linux/rcupdate.h')
-rw-r--r--include/linux/rcupdate.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index de88b33c0974..dea8f17b2fe3 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -97,6 +97,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
unsigned long secs,
unsigned long c_old,
unsigned long c);
+bool rcu_irq_enter_disabled(void);
#else
static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
int *flags,
@@ -113,6 +114,10 @@ static inline void rcutorture_record_test_transition(void)
static inline void rcutorture_record_progress(unsigned long vernum)
{
}
+static inline bool rcu_irq_enter_disabled(void)
+{
+ return false;
+}
#ifdef CONFIG_RCU_TRACE
void do_trace_rcu_torture_read(const char *rcutorturename,
struct rcu_head *rhp,