rcu: Provide better diagnostics for blocking in RCU callback functions

Currently blocking in an RCU callback function will result in
"scheduling while atomic", which could be triggered for any number
of reasons.  To aid debugging, this patch introduces a rcu_callback_map
that is used to tie the inappropriate voluntary context switch back
to the fact that the function is being invoked from within a callback.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 39cbb889e20da020c8936aae8124601b718e05a5..a94a5805d378bae7163e42259ab20e5414f62830 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -325,6 +325,7 @@ static inline void rcu_lock_release(struct lockdep_map *map)
 extern struct lockdep_map rcu_lock_map;
 extern struct lockdep_map rcu_bh_lock_map;
 extern struct lockdep_map rcu_sched_lock_map;
+extern struct lockdep_map rcu_callback_map;
 extern int debug_lockdep_rcu_enabled(void);
 
 /**

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 7859a0a3951eae09e50a11df267213af0f6bace4..a8f981a2d1109309c5e06fb79fcd5a047f11ed86 100644 (file)
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -102,13 +102,16 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 {
        unsigned long offset = (unsigned long)head->func;
 
+       rcu_lock_acquire(&rcu_callback_map);
        if (__is_kfree_rcu_offset(offset)) {
                RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
                kfree((void *)head - offset);
+               rcu_lock_release(&rcu_callback_map);
                return 1;
        } else {
                RCU_TRACE(trace_rcu_invoke_callback(rn, head));
                head->func(head);
+               rcu_lock_release(&rcu_callback_map);
                return 0;
        }
 }

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 6cb3dff89e2b73d214c9fd67d70a2abd43b64f17..802365ccd591826a60e08009a3927c9bed8c69bf 100644 (file)
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -128,6 +128,11 @@ struct lockdep_map rcu_sched_lock_map =
        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 
+static struct lock_class_key rcu_callback_key;
+struct lockdep_map rcu_callback_map =
+       STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
+EXPORT_SYMBOL_GPL(rcu_callback_map);
+
 int notrace debug_lockdep_rcu_enabled(void)
 {
        return rcu_scheduler_active && debug_locks &&