This patch targets two things which are related to ->confirm_switch:
1. Init ->confirm_switch pointer with NULL on percpu_ref_init() or
kernel frightfully complains with WARN_ON_ONCE(ref->confirm_switch)
at __percpu_ref_switch_to_atomic if memory chunk was not properly
zeroed.
2. Warn if RCU callback is still in progress on percpu_ref_exit().
The race still exists, because percpu_ref_call_confirm_rcu()
drops ->confirm_switch to NULL early, but that is only a warning
and still the caller is responsible that ref is no longer in
active use. Hopefully that can help to catch incorrect usage
of percpu-refcount.
Signed-off-by: Roman Pen <roman.peny...@profitbricks.com>
Cc: Tejun Heo <t...@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
lib/percpu-refcount.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 6111bcb..9c110e0 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -82,6 +82,7 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t
*release,
atomic_long_set(&ref->count, start_count);
ref->release = release;
+ ref->confirm_switch = NULL;
return 0;
}
EXPORT_SYMBOL_GPL(percpu_ref_init);
@@ -101,6 +102,11 @@ void percpu_ref_exit(struct percpu_ref *ref)
unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
if (percpu_count) {
+ /*
+ * Non-NULL ->confirm_switch is used to indicate that
+ * switching is in progress.
+ */
+ WARN_ON_ONCE(ref->confirm_switch);
free_percpu(percpu_count);
ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
}
--
2.9.0
