diff options
| author | Paul E. McKenney | 2020-12-08 14:43:43 -0800 |
|---|---|---|
| committer | Paul E. McKenney | 2021-01-22 15:24:23 -0800 |
| commit | 3375efeddf6972df47df26a5b5c643189bd3c02a (patch) | |
| tree | 1cbf279264fc88f0cab1a396ffdba91f54ca11d0 | |
| parent | b4b7914a6a73fc169fd1ce2fcd78a1d83d9528a9 (diff) | |
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.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| -rw-r--r-- | lib/percpu-refcount.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index e59eda07305e..a1071cdefb5a 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); |