* [PATCH RT] net: move xmit_recursion to per-task variable on -RT
@ 2016-01-13 15:23 Sebastian Andrzej Siewior
2016-01-13 17:31 ` Thomas Gleixner
0 siblings, 1 reply; 8+ messages in thread
From: Sebastian Andrzej Siewior @ 2016-01-13 15:23 UTC (permalink / raw)
To: linux-rt-users; +Cc: linux-kernel, tglx, Steven Rostedt, netdev
A softirq on -RT can be preempted. That means one task is in
__dev_queue_xmit(), gets preempted and another task may enter
__dev_queue_xmit() aw well. netperf together with a bridge device
will then trigger the `recursion alert` because each task increments
the xmit_recursion variable which is per-CPU.
A virtual device like br0 is required to trigger this warning.
This patch moves the counter to per task instead per-CPU so it counts
the recursion properly on -RT.
Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/netdevice.h | 9 +++++++++
include/linux/sched.h | 3 +++
net/core/dev.c | 41 ++++++++++++++++++++++++++++++++++++++---
3 files changed, 50 insertions(+), 3 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f14e39cb897c..4a8d3429dc12 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2249,11 +2249,20 @@ void netdev_freemem(struct net_device *dev);
void synchronize_net(void);
int init_dummy_netdev(struct net_device *dev);
+#ifdef CONFIG_PREEMPT_RT_FULL
+static inline int dev_recursion_level(void)
+{
+ return atomic_read(¤t->xmit_recursion);
+}
+
+#else
+
DECLARE_PER_CPU(int, xmit_recursion);
static inline int dev_recursion_level(void)
{
return this_cpu_read(xmit_recursion);
}
+#endif
struct net_device *dev_get_by_index(struct net *net, int ifindex);
struct net_device *__dev_get_by_index(struct net *net, int ifindex);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 04eb2f8bc274..5d36818107b0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1855,6 +1855,9 @@ struct task_struct {
pte_t kmap_pte[KM_TYPE_NR];
# endif
#endif
+#ifdef CONFIG_PREEMPT_RT_FULL
+ atomic_t xmit_recursion;
+#endif
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
unsigned long task_state_change;
#endif
diff --git a/net/core/dev.c b/net/core/dev.c
index ae4a67e7e654..1f6a7e9a22c4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2946,9 +2946,44 @@ static void skb_update_prio(struct sk_buff *skb)
#define skb_update_prio(skb)
#endif
+#ifdef CONFIG_PREEMPT_RT_FULL
+
+static inline int xmit_rec_read(void)
+{
+ return atomic_read(¤t->xmit_recursion);
+}
+
+static inline void xmit_rec_inc(void)
+{
+ atomic_inc(¤t->xmit_recursion);
+}
+
+static inline void xmit_rec_dec(void)
+{
+ atomic_dec(¤t->xmit_recursion);
+}
+
+#else
+
DEFINE_PER_CPU(int, xmit_recursion);
EXPORT_SYMBOL(xmit_recursion);
+static inline int xmit_rec_read(void)
+{
+ return __this_cpu_read(xmit_recursion);
+}
+
+static inline void xmit_rec_inc(void)
+{
+ __this_cpu_inc(xmit_recursion);
+}
+
+static inline int xmit_rec_dec(void)
+{
+ __this_cpu_dec(xmit_recursion);
+}
+#endif
+
#define RECURSION_LIMIT 10
/**
@@ -3141,7 +3176,7 @@ static int __dev_queue_xmit(struct sk_buff *skb, void *accel_priv)
if (txq->xmit_lock_owner != cpu) {
- if (__this_cpu_read(xmit_recursion) > RECURSION_LIMIT)
+ if (xmit_rec_read() > RECURSION_LIMIT)
goto recursion_alert;
skb = validate_xmit_skb(skb, dev);
@@ -3151,9 +3186,9 @@ static int __dev_queue_xmit(struct sk_buff *skb, void *accel_priv)
HARD_TX_LOCK(dev, txq, cpu);
if (!netif_xmit_stopped(txq)) {
- __this_cpu_inc(xmit_recursion);
+ xmit_rec_inc();
skb = dev_hard_start_xmit(skb, dev, txq, &rc);
- __this_cpu_dec(xmit_recursion);
+ xmit_rec_dec();
if (dev_xmit_complete(rc)) {
HARD_TX_UNLOCK(dev, txq);
goto out;
--
2.7.0.rc3
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT
2016-01-13 15:23 [PATCH RT] net: move xmit_recursion to per-task variable on -RT Sebastian Andrzej Siewior
@ 2016-01-13 17:31 ` Thomas Gleixner
2016-01-14 14:50 ` Sebastian Andrzej Siewior
0 siblings, 1 reply; 8+ messages in thread
From: Thomas Gleixner @ 2016-01-13 17:31 UTC (permalink / raw)
To: Sebastian Andrzej Siewior
Cc: linux-rt-users, linux-kernel, Steven Rostedt, netdev
On Wed, 13 Jan 2016, Sebastian Andrzej Siewior wrote:
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +static inline int dev_recursion_level(void)
> +{
> + return atomic_read(¤t->xmit_recursion);
Why would you need an atomic here. current does hardly race against itself.
Thanks,
tglx
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT
2016-01-13 17:31 ` Thomas Gleixner
@ 2016-01-14 14:50 ` Sebastian Andrzej Siewior
2016-01-14 22:02 ` Hannes Frederic Sowa
0 siblings, 1 reply; 8+ messages in thread
From: Sebastian Andrzej Siewior @ 2016-01-14 14:50 UTC (permalink / raw)
To: Thomas Gleixner; +Cc: linux-rt-users, linux-kernel, Steven Rostedt, netdev
* Thomas Gleixner | 2016-01-13 18:31:46 [+0100]:
>On Wed, 13 Jan 2016, Sebastian Andrzej Siewior wrote:
>> +#ifdef CONFIG_PREEMPT_RT_FULL
>> +static inline int dev_recursion_level(void)
>> +{
>> + return atomic_read(¤t->xmit_recursion);
>
>Why would you need an atomic here. current does hardly race against itself.
right.
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2249,11 +2249,20 @@ void netdev_freemem(struct net_device *d
void synchronize_net(void);
int init_dummy_netdev(struct net_device *dev);
+#ifdef CONFIG_PREEMPT_RT_FULL
+static inline int dev_recursion_level(void)
+{
+ return current->xmit_recursion;
+}
+
+#else
+
DECLARE_PER_CPU(int, xmit_recursion);
static inline int dev_recursion_level(void)
{
return this_cpu_read(xmit_recursion);
}
+#endif
struct net_device *dev_get_by_index(struct net *net, int ifindex);
struct net_device *__dev_get_by_index(struct net *net, int ifindex);
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1851,6 +1851,9 @@ struct task_struct {
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
unsigned long task_state_change;
#endif
+#ifdef CONFIG_PREEMPT_RT_FULL
+ int xmit_recursion;
+#endif
int pagefault_disabled;
/* CPU-specific state of this task */
struct thread_struct thread;
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2940,9 +2940,44 @@ static void skb_update_prio(struct sk_bu
#define skb_update_prio(skb)
#endif
+#ifdef CONFIG_PREEMPT_RT_FULL
+
+static inline int xmit_rec_read(void)
+{
+ return current->xmit_recursion;
+}
+
+static inline void xmit_rec_inc(void)
+{
+ current->xmit_recursion++;
+}
+
+static inline void xmit_rec_dec(void)
+{
+ current->xmit_recursion--;
+}
+
+#else
+
DEFINE_PER_CPU(int, xmit_recursion);
EXPORT_SYMBOL(xmit_recursion);
+static inline int xmit_rec_read(void)
+{
+ return __this_cpu_read(xmit_recursion);
+}
+
+static inline void xmit_rec_inc(void)
+{
+ __this_cpu_inc(xmit_recursion);
+}
+
+static inline int xmit_rec_dec(void)
+{
+ __this_cpu_dec(xmit_recursion);
+}
+#endif
+
#define RECURSION_LIMIT 10
/**
@@ -3135,7 +3170,7 @@ static int __dev_queue_xmit(struct sk_bu
if (txq->xmit_lock_owner != cpu) {
- if (__this_cpu_read(xmit_recursion) > RECURSION_LIMIT)
+ if (xmit_rec_read() > RECURSION_LIMIT)
goto recursion_alert;
skb = validate_xmit_skb(skb, dev);
@@ -3145,9 +3180,9 @@ static int __dev_queue_xmit(struct sk_bu
HARD_TX_LOCK(dev, txq, cpu);
if (!netif_xmit_stopped(txq)) {
- __this_cpu_inc(xmit_recursion);
+ xmit_rec_inc();
skb = dev_hard_start_xmit(skb, dev, txq, &rc);
- __this_cpu_dec(xmit_recursion);
+ xmit_rec_dec();
if (dev_xmit_complete(rc)) {
HARD_TX_UNLOCK(dev, txq);
goto out;
>Thanks,
>
> tglx
Sebastian
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT
2016-01-14 14:50 ` Sebastian Andrzej Siewior
@ 2016-01-14 22:02 ` Hannes Frederic Sowa
2016-01-14 22:20 ` Eric Dumazet
0 siblings, 1 reply; 8+ messages in thread
From: Hannes Frederic Sowa @ 2016-01-14 22:02 UTC (permalink / raw)
To: Sebastian Andrzej Siewior, Thomas Gleixner
Cc: linux-rt-users, linux-kernel, Steven Rostedt, netdev
On 14.01.2016 15:50, Sebastian Andrzej Siewior wrote:
> * Thomas Gleixner | 2016-01-13 18:31:46 [+0100]:
>
>> On Wed, 13 Jan 2016, Sebastian Andrzej Siewior wrote:
>>> +#ifdef CONFIG_PREEMPT_RT_FULL
>>> +static inline int dev_recursion_level(void)
>>> +{
>>> + return atomic_read(¤t->xmit_recursion);
>>
>> Why would you need an atomic here. current does hardly race against itself.
>
> right.
We are just adding a second recursion limit solely to openvswitch which
has the same problem:
https://patchwork.ozlabs.org/patch/566769/
This time also we depend on rcu_read_lock marking the section being
nonpreemptible. Nice would be a more generic solution here which doesn't
need to always add something to *current.
Thanks,
Hannes
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT
2016-01-14 22:02 ` Hannes Frederic Sowa
@ 2016-01-14 22:20 ` Eric Dumazet
2016-01-14 23:00 ` Hannes Frederic Sowa
0 siblings, 1 reply; 8+ messages in thread
From: Eric Dumazet @ 2016-01-14 22:20 UTC (permalink / raw)
To: Hannes Frederic Sowa
Cc: Sebastian Andrzej Siewior, Thomas Gleixner, linux-rt-users,
linux-kernel, Steven Rostedt, netdev
On Thu, 2016-01-14 at 23:02 +0100, Hannes Frederic Sowa wrote:
> We are just adding a second recursion limit solely to openvswitch which
> has the same problem:
>
> https://patchwork.ozlabs.org/patch/566769/
>
> This time also we depend on rcu_read_lock marking the section being
> nonpreemptible. Nice would be a more generic solution here which doesn't
> need to always add something to *current.
Note that rcu_read_lock() does not imply that preemption is disabled.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT
2016-01-14 22:20 ` Eric Dumazet
@ 2016-01-14 23:00 ` Hannes Frederic Sowa
2016-01-15 8:21 ` Thomas Gleixner
0 siblings, 1 reply; 8+ messages in thread
From: Hannes Frederic Sowa @ 2016-01-14 23:00 UTC (permalink / raw)
To: Eric Dumazet
Cc: Sebastian Andrzej Siewior, Thomas Gleixner, linux-rt-users,
linux-kernel, Steven Rostedt, netdev
On 14.01.2016 23:20, Eric Dumazet wrote:
> On Thu, 2016-01-14 at 23:02 +0100, Hannes Frederic Sowa wrote:
>
>> We are just adding a second recursion limit solely to openvswitch which
>> has the same problem:
>>
>> https://patchwork.ozlabs.org/patch/566769/
>>
>> This time also we depend on rcu_read_lock marking the section being
>> nonpreemptible. Nice would be a more generic solution here which doesn't
>> need to always add something to *current.
>
>
> Note that rcu_read_lock() does not imply that preemption is disabled.
Exactly, it is conditional on CONFIG_PREEMPT_CPU/CONFIG_PREMPT_COUNT but
haven't thought about exactly that in this moment.
I will resend this patch with better protection.
Thanks Eric!
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT
2016-01-14 23:00 ` Hannes Frederic Sowa
@ 2016-01-15 8:21 ` Thomas Gleixner
2016-01-15 9:34 ` Hannes Frederic Sowa
0 siblings, 1 reply; 8+ messages in thread
From: Thomas Gleixner @ 2016-01-15 8:21 UTC (permalink / raw)
To: Hannes Frederic Sowa
Cc: Eric Dumazet, Sebastian Andrzej Siewior, linux-rt-users,
linux-kernel, Steven Rostedt, netdev
On Fri, 15 Jan 2016, Hannes Frederic Sowa wrote:
> On 14.01.2016 23:20, Eric Dumazet wrote:
> > On Thu, 2016-01-14 at 23:02 +0100, Hannes Frederic Sowa wrote:
> >
> > > We are just adding a second recursion limit solely to openvswitch which
> > > has the same problem:
> > >
> > > https://patchwork.ozlabs.org/patch/566769/
> > >
> > > This time also we depend on rcu_read_lock marking the section being
> > > nonpreemptible. Nice would be a more generic solution here which doesn't
> > > need to always add something to *current.
> >
> >
> > Note that rcu_read_lock() does not imply that preemption is disabled.
>
> Exactly, it is conditional on CONFIG_PREEMPT_CPU/CONFIG_PREMPT_COUNT but
> haven't thought about exactly that in this moment.
Wrong. CONFIG_PREEMPT_RCU makes RCU preemptible.
If that is not set then it fiddles with preempt_count when
CONFIG_PREEMPT_COUNT=y. If CONFIG_PREEMPT_COUNT=n then you have a non
preemptible system anyway.
So you cannot assume that rcu_read_lock() disables preemption.
Thanks,
tglx
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT
2016-01-15 8:21 ` Thomas Gleixner
@ 2016-01-15 9:34 ` Hannes Frederic Sowa
0 siblings, 0 replies; 8+ messages in thread
From: Hannes Frederic Sowa @ 2016-01-15 9:34 UTC (permalink / raw)
To: Thomas Gleixner
Cc: Eric Dumazet, Sebastian Andrzej Siewior, linux-rt-users,
linux-kernel, Steven Rostedt, netdev
On 15.01.2016 09:21, Thomas Gleixner wrote:
> On Fri, 15 Jan 2016, Hannes Frederic Sowa wrote:
>> On 14.01.2016 23:20, Eric Dumazet wrote:
>>> On Thu, 2016-01-14 at 23:02 +0100, Hannes Frederic Sowa wrote:
>>>
>>>> We are just adding a second recursion limit solely to openvswitch which
>>>> has the same problem:
>>>>
>>>> https://patchwork.ozlabs.org/patch/566769/
>>>>
>>>> This time also we depend on rcu_read_lock marking the section being
>>>> nonpreemptible. Nice would be a more generic solution here which doesn't
>>>> need to always add something to *current.
>>>
>>>
>>> Note that rcu_read_lock() does not imply that preemption is disabled.
>>
>> Exactly, it is conditional on CONFIG_PREEMPT_CPU/CONFIG_PREMPT_COUNT but
>> haven't thought about exactly that in this moment.
>
> Wrong. CONFIG_PREEMPT_RCU makes RCU preemptible.
>
> If that is not set then it fiddles with preempt_count when
> CONFIG_PREEMPT_COUNT=y. If CONFIG_PREEMPT_COUNT=n then you have a non
> preemptible system anyway.
>
> So you cannot assume that rcu_read_lock() disables preemption.
Sorry for maybe writing it misleading but that is exactly what I wanted
to say here. Yes, I agree, I didn't really check because of _bh and
rcu_read_lock. This was a mistake. ;)
I already send out an updated patch with added preemption guards.
Thanks,
Hannes
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2016-01-15 9:34 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-01-13 15:23 [PATCH RT] net: move xmit_recursion to per-task variable on -RT Sebastian Andrzej Siewior
2016-01-13 17:31 ` Thomas Gleixner
2016-01-14 14:50 ` Sebastian Andrzej Siewior
2016-01-14 22:02 ` Hannes Frederic Sowa
2016-01-14 22:20 ` Eric Dumazet
2016-01-14 23:00 ` Hannes Frederic Sowa
2016-01-15 8:21 ` Thomas Gleixner
2016-01-15 9:34 ` Hannes Frederic Sowa
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.