Thread (47 messages) 47 messages, 5 authors, 2020-08-18

Re: [RFC 2/5] serial: core: Add framework to allow NMI aware serial drivers

From: Daniel Thompson <hidden>
Date: 2020-08-17 14:28:54
Also in: linux-serial, lkml

On Mon, Aug 17, 2020 at 05:57:03PM +0530, Sumit Garg wrote:
quoted hunk ↗ jump to hunk
On Fri, 14 Aug 2020 at 19:43, Daniel Thompson
[off-list ref] wrote:
quoted
On Fri, Aug 14, 2020 at 04:47:11PM +0530, Sumit Garg wrote:
Does it look better if you create a new type to map the two structures
together. Alternatively are there enough existing use-cases to want to
extend irq_work_queue() with irq_work_schedule() or something similar?
Thanks for your suggestion, irq_work_schedule() looked even better
without any overhead, see below:
diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index 3082378..1eade89 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -3,6 +3,7 @@
 #define _LINUX_IRQ_WORK_H

 #include <linux/smp_types.h>
+#include <linux/workqueue.h>

 /*
  * An entry can be in one of four states:
@@ -24,6 +25,11 @@ struct irq_work {
        void (*func)(struct irq_work *);
 };

+struct irq_work_schedule {
+       struct irq_work work;
+       struct work_struct *sched_work;
+};
+
 static inline
 void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))
 {
 {
@@ -39,6 +45,7 @@ void init_irq_work(struct irq_work *work, void
(*func)(struct irq_work *))

 bool irq_work_queue(struct irq_work *work);
 bool irq_work_queue_on(struct irq_work *work, int cpu);
+bool irq_work_schedule(struct work_struct *sched_work);

 void irq_work_tick(void);
 void irq_work_sync(struct irq_work *work);
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index eca8396..3880316 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -24,6 +24,8 @@
 static DEFINE_PER_CPU(struct llist_head, raised_list);
 static DEFINE_PER_CPU(struct llist_head, lazy_list);

+static struct irq_work_schedule irq_work_sched;
+
 /*
  * Claim the entry so that no one else will poke at it.
  */
@@ -79,6 +81,25 @@ bool irq_work_queue(struct irq_work *work)
 }
 EXPORT_SYMBOL_GPL(irq_work_queue);

+static void irq_work_schedule_fn(struct irq_work *work)
+{
+       struct irq_work_schedule *irq_work_sched =
+               container_of(work, struct irq_work_schedule, work);
+
+       if (irq_work_sched->sched_work)
+               schedule_work(irq_work_sched->sched_work);
+}
+
+/* Schedule work via irq work queue */
+bool irq_work_schedule(struct work_struct *sched_work)
+{
+       init_irq_work(&irq_work_sched.work, irq_work_schedule_fn);
+       irq_work_sched.sched_work = sched_work;
+
+       return irq_work_queue(&irq_work_sched.work);
+}
+EXPORT_SYMBOL_GPL(irq_work_schedule);
+
This is irredeemably broken.

Even if we didn't care about dropping events (which we do) then when you
overwrite irq_work_sched with a copy of another work_struct, either of
which could currently be enqueued somewhere, then you will cause some
very nasty corruption.


Daniel.

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