[PATCH 6/8] connector/cn_proc: Protect send_msg() with a local lock

Sebastian Andrzej Siewior
2020-05-19T20:20:46Z

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 | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
index d58ce664da843..055b0c86a0693 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
@@ -40,10 +41,11 @@ 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 };
+static DEFINE_LOCAL_LOCK(send_msg_lock);

static inline void send_msg(struct cn_msg *msg)
{
- preempt_disable();
+ local_lock(send_msg_lock);

msg->seq = __this_cpu_inc_return(proc_event_counts) - 1;
((struct proc_event *)msg->data)->cpu = smp_processor_id();
@@ -56,7 +58,7 @@ static inline void send_msg(struct cn_msg *msg)
*/
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_NOWAIT);

- preempt_enable();
+ local_unlock(send_msg_lock);
}

void proc_fork_connector(struct task_struct *task)
--
2.26.2