The following commit has been merged into the core/rcu branch of tip:
Commit-ID: 3375efeddf6972df47df26a5b5c643189bd3c02a
Gitweb:
https://git.kernel.org/tip/3375efeddf6972df47df26a5b5c643189bd3c02a
Author: Paul E. McKenney <paul...@kernel.org>
AuthorDate: Tue, 08 Dec 2020 14:43:43 -08:00
Committer: Paul E. McKenney <paul...@kernel.org>
CommitterDate: Fri, 22 Jan 2021 15:24:23 -08:00
percpu_ref: Dump mem_dump_obj() info upon reference-count underflow
Reference-count underflow for percpu_ref is detected in the RCU callback
percpu_ref_switch_to_atomic_rcu(), and the resulting warning does not
print anything allowing easy identification of which percpu_ref use
case is underflowing. This is of course not normally a problem when
developing a new percpu_ref use case because it is most likely that
the problem resides in this new use case. However, when deploying a
new kernel to a large set of servers, the underflow might well be a new
corner case in any of the old percpu_ref use cases.
This commit therefore calls mem_dump_obj() to dump out any additional
available information on the underflowing percpu_ref instance.
Cc: Ming Lei <ming....@redhat.com>
Cc: Jens Axboe <ax...@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo....@lge.com>
Reported-by: Andrii Nakryiko <and...@kernel.org>
Tested-by: Naresh Kamboju <naresh.kamb...@linaro.org>
Signed-off-by: Paul E. McKenney <paul...@kernel.org>
---
lib/percpu-refcount.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index e59eda0..a1071cd 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -5,6 +5,7 @@
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/slab.h>
+#include <linux/mm.h>
#include <linux/percpu-refcount.h>
/*
@@ -168,6 +169,7 @@ static void percpu_ref_switch_to_atomic_rcu(struct rcu_head
*rcu)
struct percpu_ref_data, rcu);
struct percpu_ref *ref = data->ref;
unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
+ static atomic_t underflows;
unsigned long count = 0;
int cpu;
@@ -191,9 +193,13 @@ static void percpu_ref_switch_to_atomic_rcu(struct
rcu_head *rcu)
*/
atomic_long_add((long)count - PERCPU_COUNT_BIAS, &data->count);
- WARN_ONCE(atomic_long_read(&data->count) <= 0,
- "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
- data->release, atomic_long_read(&data->count));
+ if (WARN_ONCE(atomic_long_read(&data->count) <= 0,
+ "percpu ref (%ps) <= 0 (%ld) after switching to atomic",
+ data->release, atomic_long_read(&data->count)) &&
+ atomic_inc_return(&underflows) < 4) {
+ pr_err("%s(): percpu_ref underflow", __func__);
+ mem_dump_obj(data);
+ }
/* @ref is viewed as dead on all CPUs, send out switch confirmation */
percpu_ref_call_confirm_rcu(rcu);
