[PATCH v2 sl-b 4/5] rcu: Make call_rcu() print mem_dump_obj() info for double-freed callback

paulmck
2020-12-09T01:13:12Z

From: "Paul E. McKenney" <paulmck@kernel.org>

The debug-object double-free checks in __call_rcu() print out the
RCU callback function, which is usually sufficient to track down the
double free. However, all uses of things like queue_rcu_work() will
have the same RCU callback function (rcu_work_rcufn() in this case),
so a diagnostic message for a double queue_rcu_work() needs more than
just the callback function.

This commit therefore calls mem_dump_obj() to dump out any additional
available information on the double-freed callback.

Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b6c9c49..464cf14 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2957,6 +2957,7 @@ static void check_cb_ovld(struct rcu_data *rdp)
static void
__call_rcu(struct rcu_head *head, rcu_callback_t func)
{
+ static atomic_t doublefrees;
unsigned long flags;
struct rcu_data *rdp;
bool was_alldone;
@@ -2970,8 +2971,10 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
* Use rcu:rcu_callback trace event to find the previous
* time callback was passed to __call_rcu().
*/
- WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pS()!!!\n",
- head, head->func);
+ if (atomic_inc_return(&doublefrees) < 4) {
+ pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
+ mem_dump_obj(head);
+ }
WRITE_ONCE(head->func, rcu_leak_callback);
return;
}
--
2.9.5