ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 219 insertions, 0 deletions

diff --git a/lib/irq_poll.c b/lib/irq_poll.c
new file mode 100644
index 000000000..08b242bbd
--- /dev/null
+++ b/lib/irq_poll.c
@@ -0,0 +1,219 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Functions related to interrupt-poll handling in the block layer. This
+ * is similar to NAPI for network devices.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/bio.h>
+#include <linux/interrupt.h>
+#include <linux/cpu.h>
+#include <linux/irq_poll.h>
+#include <linux/delay.h>
+
+static unsigned int irq_poll_budget __read_mostly = 256;
+
+static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
+
+/**
+ * irq_poll_sched - Schedule a run of the iopoll handler
+ * @iop:      The parent iopoll structure
+ *
+ * Description:
+ *     Add this irq_poll structure to the pending poll list and trigger the
+ *     raise of the blk iopoll softirq.
+ **/
+void irq_poll_sched(struct irq_poll *iop)
+{
+	unsigned long flags;
+
+	if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
+		return;
+	if (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
+		return;
+
+	local_irq_save(flags);
+	list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
+	raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL(irq_poll_sched);
+
+/**
+ * __irq_poll_complete - Mark this @iop as un-polled again
+ * @iop:      The parent iopoll structure
+ *
+ * Description:
+ *     See irq_poll_complete(). This function must be called with interrupts
+ *     disabled.
+ **/
+static void __irq_poll_complete(struct irq_poll *iop)
+{
+	list_del(&iop->list);
+	smp_mb__before_atomic();
+	clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
+}
+
+/**
+ * irq_poll_complete - Mark this @iop as un-polled again
+ * @iop:      The parent iopoll structure
+ *
+ * Description:
+ *     If a driver consumes less than the assigned budget in its run of the
+ *     iopoll handler, it'll end the polled mode by calling this function. The
+ *     iopoll handler will not be invoked again before irq_poll_sched()
+ *     is called.
+ **/
+void irq_poll_complete(struct irq_poll *iop)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	__irq_poll_complete(iop);
+	local_irq_restore(flags);
+}
+EXPORT_SYMBOL(irq_poll_complete);
+
+static void __latent_entropy irq_poll_softirq(void)
+{
+	struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
+	int rearm = 0, budget = irq_poll_budget;
+	unsigned long start_time = jiffies;
+
+	local_irq_disable();
+
+	while (!list_empty(list)) {
+		struct irq_poll *iop;
+		int work, weight;
+
+		/*
+		 * If softirq window is exhausted then punt.
+		 */
+		if (budget <= 0 || time_after(jiffies, start_time)) {
+			rearm = 1;
+			break;
+		}
+
+		local_irq_enable();
+
+		/* Even though interrupts have been re-enabled, this
+		 * access is safe because interrupts can only add new
+		 * entries to the tail of this list, and only ->poll()
+		 * calls can remove this head entry from the list.
+		 */
+		iop = list_entry(list->next, struct irq_poll, list);
+
+		weight = iop->weight;
+		work = 0;
+		if (test_bit(IRQ_POLL_F_SCHED, &iop->state))
+			work = iop->poll(iop, weight);
+
+		budget -= work;
+
+		local_irq_disable();
+
+		/*
+		 * Drivers must not modify the iopoll state, if they
+		 * consume their assigned weight (or more, some drivers can't
+		 * easily just stop processing, they have to complete an
+		 * entire mask of commands).In such cases this code
+		 * still "owns" the iopoll instance and therefore can
+		 * move the instance around on the list at-will.
+		 */
+		if (work >= weight) {
+			if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
+				__irq_poll_complete(iop);
+			else
+				list_move_tail(&iop->list, list);
+		}
+	}
+
+	if (rearm)
+		__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
+
+	local_irq_enable();
+}
+
+/**
+ * irq_poll_disable - Disable iopoll on this @iop
+ * @iop:      The parent iopoll structure
+ *
+ * Description:
+ *     Disable io polling and wait for any pending callbacks to have completed.
+ **/
+void irq_poll_disable(struct irq_poll *iop)
+{
+	set_bit(IRQ_POLL_F_DISABLE, &iop->state);
+	while (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
+		msleep(1);
+	clear_bit(IRQ_POLL_F_DISABLE, &iop->state);
+}
+EXPORT_SYMBOL(irq_poll_disable);
+
+/**
+ * irq_poll_enable - Enable iopoll on this @iop
+ * @iop:      The parent iopoll structure
+ *
+ * Description:
+ *     Enable iopoll on this @iop. Note that the handler run will not be
+ *     scheduled, it will only mark it as active.
+ **/
+void irq_poll_enable(struct irq_poll *iop)
+{
+	BUG_ON(!test_bit(IRQ_POLL_F_SCHED, &iop->state));
+	smp_mb__before_atomic();
+	clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
+}
+EXPORT_SYMBOL(irq_poll_enable);
+
+/**
+ * irq_poll_init - Initialize this @iop
+ * @iop:      The parent iopoll structure
+ * @weight:   The default weight (or command completion budget)
+ * @poll_fn:  The handler to invoke
+ *
+ * Description:
+ *     Initialize and enable this irq_poll structure.
+ **/
+void irq_poll_init(struct irq_poll *iop, int weight, irq_poll_fn *poll_fn)
+{
+	memset(iop, 0, sizeof(*iop));
+	INIT_LIST_HEAD(&iop->list);
+	iop->weight = weight;
+	iop->poll = poll_fn;
+}
+EXPORT_SYMBOL(irq_poll_init);
+
+static int irq_poll_cpu_dead(unsigned int cpu)
+{
+	/*
+	 * If a CPU goes away, splice its entries to the current CPU and
+	 * set the POLL softirq bit. The local_bh_disable()/enable() pair
+	 * ensures that it is handled. Otherwise the current CPU could
+	 * reach idle with the POLL softirq pending.
+	 */
+	local_bh_disable();
+	local_irq_disable();
+	list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
+			 this_cpu_ptr(&blk_cpu_iopoll));
+	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
+	local_irq_enable();
+	local_bh_enable();
+
+	return 0;
+}
+
+static __init int irq_poll_setup(void)
+{
+	int i;
+
+	for_each_possible_cpu(i)
+		INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
+
+	open_softirq(IRQ_POLL_SOFTIRQ, irq_poll_softirq);
+	cpuhp_setup_state_nocalls(CPUHP_IRQ_POLL_DEAD, "irq_poll:dead", NULL,
+				  irq_poll_cpu_dead);
+	return 0;
+}
+subsys_initcall(irq_poll_setup);