irq_work: Convert flags to atomic_t

We need to convert flags to atomic_t in order to later fix an ordering
issue on atomic_cmpxchg() failure. This will allow us to use atomic_fetch_or().

Also clarify the nature of those flags.

[ mingo: Converted two more usage site the original patch missed. ]

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191108160858.31665-2-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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);

kernel/bpf/stackmap.c

@@ -289,7 +289,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
 
 	if (in_nmi()) {
 		work = this_cpu_ptr(&up_read_work);
-		if (work->irq_work.flags & IRQ_WORK_BUSY)
+		if (atomic_read(&work->irq_work.flags) & IRQ_WORK_BUSY)
 			/* cannot queue more up_read, fallback */
 			irq_work_busy = true;
 	}

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;
+		flags = atomic_read(&work->flags) & ~IRQ_WORK_PENDING;
-		xchg(&work->flags, flags);
+		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);

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)

kernel/trace/bpf_trace.c

@@ -660,7 +660,7 @@ BPF_CALL_1(bpf_send_signal, u32, sig)
 			return -EINVAL;
 
 		work = this_cpu_ptr(&send_signal_work);
-		if (work->irq_work.flags & IRQ_WORK_BUSY)
+		if (atomic_read(&work->irq_work.flags) & IRQ_WORK_BUSY)
 			return -EBUSY;
 
 		/* Add the current task, which is the target of sending signal,