[PATCH 1/4] irq_work: Convert flags to atomic_t

Frederic Weisbecker
2019-11-08T16:09:27Z

We need to convert flags to atomic_t in order to later fix an ordering
issue on cmpxchg() failure. This will allow us to use atomic_fetch_or().
Also that clarify the nature of those flags.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
---
include/linux/irq_work.h | 10 +++++++---
kernel/irq_work.c | 18 +++++++++---------
kernel/printk/printk.c | 2 +-
3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index b11fcdfd0770..02da997ad12c 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -22,7 +22,7 @@
#define IRQ_WORK_CLAIMED (IRQ_WORK_PENDING | IRQ_WORK_BUSY)

struct irq_work {
- unsigned long flags;
+ atomic_t flags;
struct llist_node llnode;
void (*func)(struct irq_work *);
};
@@ -30,11 +30,15 @@ struct irq_work {
static inline
void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))
{
- work->flags = 0;
+ atomic_set(&work->flags, 0);
work->func = func;
}

-#define DEFINE_IRQ_WORK(name, _f) struct irq_work name = { .func = (_f), }
+#define DEFINE_IRQ_WORK(name, _f) struct irq_work name = { \
+ .flags = ATOMIC_INIT(0), \
+ .func = (_f) \
+}
+

bool irq_work_queue(struct irq_work *work);
bool irq_work_queue_on(struct irq_work *work, int cpu);
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index d42acaf81886..df0dbf4d859b 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -29,16 +29,16 @@ static DEFINE_PER_CPU(struct llist_head, lazy_list);
*/
static bool irq_work_claim(struct irq_work *work)
{
- unsigned long flags, oflags, nflags;
+ int flags, oflags, nflags;

/*
* Start with our best wish as a premise but only trust any
* flag value after cmpxchg() result.
*/
- flags = work->flags & ~IRQ_WORK_PENDING;
+ flags = atomic_read(&work->flags) & ~IRQ_WORK_PENDING;
for (;;) {
nflags = flags | IRQ_WORK_CLAIMED;
- oflags = cmpxchg(&work->flags, flags, nflags);
+ oflags = atomic_cmpxchg(&work->flags, flags, nflags);
if (oflags == flags)
break;
if (oflags & IRQ_WORK_PENDING)
@@ -61,7 +61,7 @@ void __weak arch_irq_work_raise(void)
static void __irq_work_queue_local(struct irq_work *work)
{
/* If the work is "lazy", handle it from next tick if any */
- if (work->flags & IRQ_WORK_LAZY) {
+ if (atomic_read(&work->flags) & IRQ_WORK_LAZY) {
if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
tick_nohz_tick_stopped())
arch_irq_work_raise();
@@ -143,7 +143,7 @@ static void irq_work_run_list(struct llist_head *list)
{
struct irq_work *work, *tmp;
struct llist_node *llnode;
- unsigned long flags;
+ int flags;

BUG_ON(!irqs_disabled());

@@ -159,15 +159,15 @@ static void irq_work_run_list(struct llist_head *list)
* to claim that work don't rely on us to handle their data
* while we are in the middle of the func.
*/
- flags = work->flags & ~IRQ_WORK_PENDING;
- xchg(&work->flags, flags);
+ flags = atomic_read(&work->flags) & ~IRQ_WORK_PENDING;
+ atomic_xchg(&work->flags, flags);

work->func(work);
/*
* Clear the BUSY bit and return to the free state if
* no-one else claimed it meanwhile.
*/
- (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
+ (void)atomic_cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
}
}

@@ -199,7 +199,7 @@ void irq_work_sync(struct irq_work *work)
{
lockdep_assert_irqs_enabled();

- while (work->flags & IRQ_WORK_BUSY)
+ while (atomic_read(&work->flags) & IRQ_WORK_BUSY)
cpu_relax();
}
EXPORT_SYMBOL_GPL(irq_work_sync);
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ca65327a6de8..865727373a3b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2961,7 +2961,7 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work)

static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) = {
.func = wake_up_klogd_work_func,
- .flags = IRQ_WORK_LAZY,
+ .flags = ATOMIC_INIT(IRQ_WORK_LAZY),
};

void wake_up_klogd(void)
--
2.23.0