* [PATCH v2 5/7] connector/cn_proc: Protect send_msg() with a local lock
[not found] <20200524215739.551568-1-bigeasy@linutronix.de>
@ 2020-05-24 21:57 ` Sebastian Andrzej Siewior
2020-05-25 7:18 ` Ingo Molnar
0 siblings, 1 reply; 3+ messages in thread
From: Sebastian Andrzej Siewior @ 2020-05-24 21:57 UTC (permalink / raw)
To: linux-kernel
Cc: Peter Zijlstra, Ingo Molnar, Steven Rostedt, Will Deacon,
Thomas Gleixner, Paul E . McKenney, Linus Torvalds,
Matthew Wilcox, Mike Galbraith, Evgeniy Polyakov, netdev,
Sebastian Andrzej Siewior
From: Mike Galbraith <umgwanakikbuti@gmail.com>
send_msg() disables preemption to avoid out-of-order messages. As the
code inside the preempt disabled section acquires regular spinlocks,
which are converted to 'sleeping' spinlocks on a PREEMPT_RT kernel and
eventually calls into a memory allocator, this conflicts with the RT
semantics.
Convert it to a local_lock which allows RT kernels to substitute them with
a real per CPU lock. On non RT kernels this maps to preempt_disable() as
before. No functional change.
[bigeasy: Patch description]
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
drivers/connector/cn_proc.c | 22 +++++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)
diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
index d58ce664da843..d424d1f469136 100644
--- a/drivers/connector/cn_proc.c
+++ b/drivers/connector/cn_proc.c
@@ -18,6 +18,7 @@
#include <linux/pid_namespace.h>
#include <linux/cn_proc.h>
+#include <linux/locallock.h>
/*
* Size of a cn_msg followed by a proc_event structure. Since the
@@ -38,25 +39,32 @@ static inline struct cn_msg *buffer_to_cn_msg(__u8 *buffer)
static atomic_t proc_event_num_listeners = ATOMIC_INIT(0);
static struct cb_id cn_proc_event_id = { CN_IDX_PROC, CN_VAL_PROC };
-/* proc_event_counts is used as the sequence number of the netlink message */
-static DEFINE_PER_CPU(__u32, proc_event_counts) = { 0 };
+/* local_evt.counts is used as the sequence number of the netlink message */
+struct local_evt {
+ __u32 counts;
+ struct local_lock lock;
+};
+static DEFINE_PER_CPU(struct local_evt, local_evt) = {
+ .counts = 0,
+ .lock = INIT_LOCAL_LOCK(lock),
+};
static inline void send_msg(struct cn_msg *msg)
{
- preempt_disable();
+ local_lock(&local_evt.lock);
- msg->seq = __this_cpu_inc_return(proc_event_counts) - 1;
+ msg->seq = __this_cpu_inc_return(local_evt.counts) - 1;
((struct proc_event *)msg->data)->cpu = smp_processor_id();
/*
- * Preemption remains disabled during send to ensure the messages are
- * ordered according to their sequence numbers.
+ * local_lock() disables preemption during send to ensure the messages
+ * are ordered according to their sequence numbers.
*
* If cn_netlink_send() fails, the data is not sent.
*/
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_NOWAIT);
- preempt_enable();
+ local_unlock(&local_evt.lock);
}
void proc_fork_connector(struct task_struct *task)
--
2.27.0.rc0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2 5/7] connector/cn_proc: Protect send_msg() with a local lock
2020-05-24 21:57 ` [PATCH v2 5/7] connector/cn_proc: Protect send_msg() with a local lock Sebastian Andrzej Siewior
@ 2020-05-25 7:18 ` Ingo Molnar
2020-05-25 14:51 ` Sebastian Andrzej Siewior
0 siblings, 1 reply; 3+ messages in thread
From: Ingo Molnar @ 2020-05-25 7:18 UTC (permalink / raw)
To: Sebastian Andrzej Siewior
Cc: linux-kernel, Peter Zijlstra, Steven Rostedt, Will Deacon,
Thomas Gleixner, Paul E . McKenney, Linus Torvalds,
Matthew Wilcox, Mike Galbraith, Evgeniy Polyakov, netdev
* Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> From: Mike Galbraith <umgwanakikbuti@gmail.com>
>
> send_msg() disables preemption to avoid out-of-order messages. As the
> code inside the preempt disabled section acquires regular spinlocks,
> which are converted to 'sleeping' spinlocks on a PREEMPT_RT kernel and
> eventually calls into a memory allocator, this conflicts with the RT
> semantics.
>
> Convert it to a local_lock which allows RT kernels to substitute them with
> a real per CPU lock. On non RT kernels this maps to preempt_disable() as
> before. No functional change.
>
> [bigeasy: Patch description]
>
> Cc: Evgeniy Polyakov <zbr@ioremap.net>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> drivers/connector/cn_proc.c | 22 +++++++++++++++-------
> 1 file changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> index d58ce664da843..d424d1f469136 100644
> --- a/drivers/connector/cn_proc.c
> +++ b/drivers/connector/cn_proc.c
> @@ -18,6 +18,7 @@
> #include <linux/pid_namespace.h>
>
> #include <linux/cn_proc.h>
> +#include <linux/locallock.h>
>
> /*
> * Size of a cn_msg followed by a proc_event structure. Since the
> @@ -38,25 +39,32 @@ static inline struct cn_msg *buffer_to_cn_msg(__u8 *buffer)
> static atomic_t proc_event_num_listeners = ATOMIC_INIT(0);
> static struct cb_id cn_proc_event_id = { CN_IDX_PROC, CN_VAL_PROC };
>
> -/* proc_event_counts is used as the sequence number of the netlink message */
> -static DEFINE_PER_CPU(__u32, proc_event_counts) = { 0 };
> +/* local_evt.counts is used as the sequence number of the netlink message */
> +struct local_evt {
> + __u32 counts;
> + struct local_lock lock;
> +};
> +static DEFINE_PER_CPU(struct local_evt, local_evt) = {
> + .counts = 0,
I don't think zero initializations need to be written out explicitly.
> + .lock = INIT_LOCAL_LOCK(lock),
> +};
>
> static inline void send_msg(struct cn_msg *msg)
> {
> - preempt_disable();
> + local_lock(&local_evt.lock);
>
> - msg->seq = __this_cpu_inc_return(proc_event_counts) - 1;
> + msg->seq = __this_cpu_inc_return(local_evt.counts) - 1;
Naming nit: renaming this from 'proc_event_counts' to
'local_evt.counts' is a step back IMO - what's an 'evt',
did we run out of e's? ;-)
Should be something like local_event.count? (Singular.)
Thanks,
Ingo
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2 5/7] connector/cn_proc: Protect send_msg() with a local lock
2020-05-25 7:18 ` Ingo Molnar
@ 2020-05-25 14:51 ` Sebastian Andrzej Siewior
0 siblings, 0 replies; 3+ messages in thread
From: Sebastian Andrzej Siewior @ 2020-05-25 14:51 UTC (permalink / raw)
To: Ingo Molnar
Cc: linux-kernel, Peter Zijlstra, Steven Rostedt, Will Deacon,
Thomas Gleixner, Paul E . McKenney, Linus Torvalds,
Matthew Wilcox, Mike Galbraith, Evgeniy Polyakov, netdev
On 2020-05-25 09:18:19 [+0200], Ingo Molnar wrote:
> > +static DEFINE_PER_CPU(struct local_evt, local_evt) = {
> > + .counts = 0,
>
> I don't think zero initializations need to be written out explicitly.
yes.
> > + .lock = INIT_LOCAL_LOCK(lock),
> > +};
> >
> > static inline void send_msg(struct cn_msg *msg)
> > {
> > - preempt_disable();
> > + local_lock(&local_evt.lock);
> >
> > - msg->seq = __this_cpu_inc_return(proc_event_counts) - 1;
> > + msg->seq = __this_cpu_inc_return(local_evt.counts) - 1;
>
> Naming nit: renaming this from 'proc_event_counts' to
> 'local_evt.counts' is a step back IMO - what's an 'evt',
> did we run out of e's? ;-)
>
> Should be something like local_event.count? (Singular.)
okay.
> Thanks,
>
> Ingo
Sebastian
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2020-05-24 21:57 ` [PATCH v2 5/7] connector/cn_proc: Protect send_msg() with a local lock Sebastian Andrzej Siewior
2020-05-25 7:18 ` Ingo Molnar
2020-05-25 14:51 ` Sebastian Andrzej Siewior
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