* [PATCH net-next v3 0/2] Add an assert in napi_consume_skb()
@ 2020-11-24 10:49 Yunsheng Lin
2020-11-24 10:49 ` [PATCH net-next v3 1/2] lockdep: Introduce in_softirq lockdep assert Yunsheng Lin
2020-11-24 10:49 ` [PATCH net-next v3 2/2] net: Use lockdep_assert_in_softirq() in napi_consume_skb() Yunsheng Lin
0 siblings, 2 replies; 4+ messages in thread
From: Yunsheng Lin @ 2020-11-24 10:49 UTC (permalink / raw)
To: peterz, mingo, will, viro, kyk.segfault, davem, kuba, linmiaohe,
martin.varghese, pabeni, pshelar, fw, gnault, steffen.klassert,
vladimir.oltean, edumazet, saeed
Cc: netdev, linux-kernel, linuxarm
This patch introduces a lockdep_assert_in_softirq() interface and
uses it to assert the case when napi_consume_skb() is not called in
the softirq context.
Changelog:
V3: add comment to emphasize the ambiguous semantics
V2: Use lockdep instead of one-off Kconfig knob
Yunsheng Lin (2):
lockdep: Introduce in_softirq lockdep assert
net: Use lockdep_assert_in_softirq() in napi_consume_skb()
include/linux/lockdep.h | 8 ++++++++
net/core/skbuff.c | 2 ++
2 files changed, 10 insertions(+)
--
2.8.1
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH net-next v3 1/2] lockdep: Introduce in_softirq lockdep assert
2020-11-24 10:49 [PATCH net-next v3 0/2] Add an assert in napi_consume_skb() Yunsheng Lin
@ 2020-11-24 10:49 ` Yunsheng Lin
2020-11-25 23:11 ` Jakub Kicinski
2020-11-24 10:49 ` [PATCH net-next v3 2/2] net: Use lockdep_assert_in_softirq() in napi_consume_skb() Yunsheng Lin
1 sibling, 1 reply; 4+ messages in thread
From: Yunsheng Lin @ 2020-11-24 10:49 UTC (permalink / raw)
To: peterz, mingo, will, viro, kyk.segfault, davem, kuba, linmiaohe,
martin.varghese, pabeni, pshelar, fw, gnault, steffen.klassert,
vladimir.oltean, edumazet, saeed
Cc: netdev, linux-kernel, linuxarm
The current semantic for napi_consume_skb() is that caller need
to provide non-zero budget when calling from NAPI context, and
breaking this semantic will cause hard to debug problem, because
_kfree_skb_defer() need to run in atomic context in order to push
the skb to the particular cpu' napi_alloc_cache atomically.
So add the lockdep_assert_in_softirq() to assert when the running
context is not in_softirq, in_softirq means softirq is serving or
BH is disabled, which has a ambiguous semantics due to the BH
disabled confusion, so add a comment to emphasize that.
And the softirq context can be interrupted by hard IRQ or NMI
context, lockdep_assert_in_softirq() need to assert about hard
IRQ or NMI context too.
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
---
V3: add comment to emphasize the ambiguous semantics.
---
include/linux/lockdep.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index f559487..8d60f46 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -594,6 +594,13 @@ do { \
this_cpu_read(hardirqs_enabled))); \
} while (0)
+/* Much like in_softirq() - semantics are ambiguous, use carefully. */
+#define lockdep_assert_in_softirq() \
+do { \
+ WARN_ON_ONCE(__lockdep_enabled && \
+ (!in_softirq() || in_irq() || in_nmi())); \
+} while (0)
+
#else
# define might_lock(lock) do { } while (0)
# define might_lock_read(lock) do { } while (0)
@@ -605,6 +612,7 @@ do { \
# define lockdep_assert_preemption_enabled() do { } while (0)
# define lockdep_assert_preemption_disabled() do { } while (0)
+# define lockdep_assert_in_softirq() do { } while (0)
#endif
#ifdef CONFIG_PROVE_RAW_LOCK_NESTING
--
2.8.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH net-next v3 2/2] net: Use lockdep_assert_in_softirq() in napi_consume_skb()
2020-11-24 10:49 [PATCH net-next v3 0/2] Add an assert in napi_consume_skb() Yunsheng Lin
2020-11-24 10:49 ` [PATCH net-next v3 1/2] lockdep: Introduce in_softirq lockdep assert Yunsheng Lin
@ 2020-11-24 10:49 ` Yunsheng Lin
1 sibling, 0 replies; 4+ messages in thread
From: Yunsheng Lin @ 2020-11-24 10:49 UTC (permalink / raw)
To: peterz, mingo, will, viro, kyk.segfault, davem, kuba, linmiaohe,
martin.varghese, pabeni, pshelar, fw, gnault, steffen.klassert,
vladimir.oltean, edumazet, saeed
Cc: netdev, linux-kernel, linuxarm
Use napi_consume_skb() to assert the case when it is not called
in a atomic softirq context.
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
---
net/core/skbuff.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index ffe3dcc..effa19d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -902,6 +902,8 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
return;
}
+ lockdep_assert_in_softirq();
+
if (!skb_unref(skb))
return;
--
2.8.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH net-next v3 1/2] lockdep: Introduce in_softirq lockdep assert
2020-11-24 10:49 ` [PATCH net-next v3 1/2] lockdep: Introduce in_softirq lockdep assert Yunsheng Lin
@ 2020-11-25 23:11 ` Jakub Kicinski
0 siblings, 0 replies; 4+ messages in thread
From: Jakub Kicinski @ 2020-11-25 23:11 UTC (permalink / raw)
To: Yunsheng Lin
Cc: peterz, mingo, will, viro, kyk.segfault, davem, linmiaohe,
martin.varghese, pabeni, pshelar, fw, gnault, steffen.klassert,
vladimir.oltean, edumazet, saeed, netdev, linux-kernel, linuxarm
On Tue, 24 Nov 2020 18:49:28 +0800 Yunsheng Lin wrote:
> The current semantic for napi_consume_skb() is that caller need
> to provide non-zero budget when calling from NAPI context, and
> breaking this semantic will cause hard to debug problem, because
> _kfree_skb_defer() need to run in atomic context in order to push
> the skb to the particular cpu' napi_alloc_cache atomically.
>
> So add the lockdep_assert_in_softirq() to assert when the running
> context is not in_softirq, in_softirq means softirq is serving or
> BH is disabled, which has a ambiguous semantics due to the BH
> disabled confusion, so add a comment to emphasize that.
>
> And the softirq context can be interrupted by hard IRQ or NMI
> context, lockdep_assert_in_softirq() need to assert about hard
> IRQ or NMI context too.
>
> Suggested-by: Jakub Kicinski <kuba@kernel.org>
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> ---
> V3: add comment to emphasize the ambiguous semantics.
> ---
> include/linux/lockdep.h | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index f559487..8d60f46 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -594,6 +594,13 @@ do { \
> this_cpu_read(hardirqs_enabled))); \
> } while (0)
>
> +/* Much like in_softirq() - semantics are ambiguous, use carefully. */
I've added both of the comments I suggested in the reply to Peter here
and applied to net-next.
Thanks for working on this.
> +#define lockdep_assert_in_softirq() \
> +do { \
> + WARN_ON_ONCE(__lockdep_enabled && \
> + (!in_softirq() || in_irq() || in_nmi())); \
> +} while (0)
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-11-25 23:12 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2020-11-24 10:49 [PATCH net-next v3 0/2] Add an assert in napi_consume_skb() Yunsheng Lin
2020-11-24 10:49 ` [PATCH net-next v3 1/2] lockdep: Introduce in_softirq lockdep assert Yunsheng Lin
2020-11-25 23:11 ` Jakub Kicinski
2020-11-24 10:49 ` [PATCH net-next v3 2/2] net: Use lockdep_assert_in_softirq() in napi_consume_skb() Yunsheng Lin
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