* [PATCH 1/1] percpu-refcount: init ->confirm_switch member properly
@ 2016-08-11 17:27 Roman Pen
2016-08-11 20:25 ` Tejun Heo
0 siblings, 1 reply; 2+ messages in thread
From: Roman Pen @ 2016-08-11 17:27 UTC (permalink / raw)
Cc: Roman Pen, Tejun Heo, linux-kernel
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.penyaev@profitbricks.com>
Cc: Tejun Heo <tj@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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH 1/1] percpu-refcount: init ->confirm_switch member properly
2016-08-11 17:27 [PATCH 1/1] percpu-refcount: init ->confirm_switch member properly Roman Pen
@ 2016-08-11 20:25 ` Tejun Heo
0 siblings, 0 replies; 2+ messages in thread
From: Tejun Heo @ 2016-08-11 20:25 UTC (permalink / raw)
To: Roman Pen; +Cc: linux-kernel
On Thu, Aug 11, 2016 at 07:27:09PM +0200, Roman Pen wrote:
> 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.penyaev@profitbricks.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: linux-kernel@vger.kernel.org
Applied to percpu/for-4.9.
Thanks.
--
tejun
^ permalink raw reply [flat|nested] 2+ messages in thread
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