Messages in this thread Patch in this message | | | From | Roman Pen <> | Subject | [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier() just before freeing | Date | Wed, 10 Aug 2016 21:55:39 +0200 |
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percpu issues some RCU callbacks to synchronize its state, so before freeing we have to wait all those callbacks to finish.
E.g. the following simple sequence on stack causes nasty crash:
struct percpu_ref ref;
percpu_ref_init(&ref, release, 0, GFP_KERNEL); percpu_ref_kill(&ref); percpu_ref_exit(&ref);
Also this patch includes inition to NULL of confirm_switch callback. Without this inition you have to zero out a chunk of memory or kernel frightfully complains with WARN_ON_ONCE(ref->confirm_switch) at __percpu_ref_switch_to_atomic.
Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com> Cc: Tejun Heo <tj@kernel.org> Cc: linux-kernel@vger.kernel.org --- v2: - just sending one more time because v1 was accidently sent as a reply to not related issue.
lib/percpu-refcount.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index 6111bcb..ddf934b 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 +102,7 @@ void percpu_ref_exit(struct percpu_ref *ref) unsigned long __percpu *percpu_count = percpu_count_ptr(ref); if (percpu_count) { + rcu_barrier_sched(); free_percpu(percpu_count); ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD; } -- 2.9.0
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