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, 244 insertions, 0 deletions

diff --git a/drivers/virt/acrn/irqfd.c b/drivers/virt/acrn/irqfd.c
new file mode 100644
index 000000000..ac583c843
--- /dev/null
+++ b/drivers/virt/acrn/irqfd.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ACRN HSM irqfd: use eventfd objects to inject virtual interrupts
+ *
+ * Copyright (C) 2020 Intel Corporation. All rights reserved.
+ *
+ * Authors:
+ *	Shuo Liu <shuo.a.liu@intel.com>
+ *	Yakui Zhao <yakui.zhao@intel.com>
+ */
+
+#include <linux/eventfd.h>
+#include <linux/file.h>
+#include <linux/poll.h>
+#include <linux/slab.h>
+
+#include "acrn_drv.h"
+
+/* Cleanup work has been queued; set via test_and_set_bit(). */
+#define HSM_IRQFD_FLAG_SHUTDOWN	0
+
+/**
+ * struct hsm_irqfd - Properties of HSM irqfd
+ * @vm:		Associated VM pointer
+ * @wait:	Entry of wait-queue
+ * @shutdown:	Async shutdown work
+ * @eventfd:	Associated eventfd
+ * @list:	Entry within &acrn_vm.irqfds of irqfds of a VM
+ * @pt:		Structure for select/poll on the associated eventfd
+ * @msi:	MSI data
+ * @flags:	Internal lifecycle flags (HSM_IRQFD_FLAG_*)
+ */
+struct hsm_irqfd {
+	struct acrn_vm		*vm;
+	wait_queue_entry_t	wait;
+	struct work_struct	shutdown;
+	struct eventfd_ctx	*eventfd;
+	struct list_head	list;
+	poll_table		pt;
+	struct acrn_msi_entry	msi;
+	unsigned long		flags;
+};
+
+static void acrn_irqfd_inject(struct hsm_irqfd *irqfd)
+{
+	struct acrn_vm *vm = irqfd->vm;
+
+	acrn_msi_inject(vm, irqfd->msi.msi_addr,
+			irqfd->msi.msi_data);
+}
+
+/* Queue the cleanup work at most once. Safe from atomic context. */
+static void hsm_irqfd_queue_shutdown(struct hsm_irqfd *irqfd)
+{
+	if (!test_and_set_bit(HSM_IRQFD_FLAG_SHUTDOWN, &irqfd->flags))
+		queue_work(irqfd->vm->irqfd_wq, &irqfd->shutdown);
+}
+
+/* Sole owner of @irqfd: unhook waitqueue, drop eventfd ref, free. */
+static void hsm_irqfd_shutdown_work(struct work_struct *work)
+{
+	struct hsm_irqfd *irqfd = container_of(work, struct hsm_irqfd,
+					       shutdown);
+	struct acrn_vm *vm = irqfd->vm;
+	u64 cnt;
+
+	mutex_lock(&vm->irqfds_lock);
+	if (!list_empty(&irqfd->list))
+		list_del_init(&irqfd->list);
+	mutex_unlock(&vm->irqfds_lock);
+
+	eventfd_ctx_remove_wait_queue(irqfd->eventfd, &irqfd->wait, &cnt);
+	eventfd_ctx_put(irqfd->eventfd);
+	kfree(irqfd);
+}
+
+/* Called with wqh->lock held and interrupts disabled */
+static int hsm_irqfd_wakeup(wait_queue_entry_t *wait, unsigned int mode,
+			    int sync, void *key)
+{
+	unsigned long poll_bits = (unsigned long)key;
+	struct hsm_irqfd *irqfd;
+
+	irqfd = container_of(wait, struct hsm_irqfd, wait);
+
+	if (poll_bits & POLLIN)
+		/* An event has been signaled, inject an interrupt */
+		acrn_irqfd_inject(irqfd);
+
+	if (poll_bits & POLLHUP)
+		/* Defer teardown to the cleanup work; can't sleep here. */
+		hsm_irqfd_queue_shutdown(irqfd);
+
+	return 0;
+}
+
+static void hsm_irqfd_poll_func(struct file *file, wait_queue_head_t *wqh,
+				poll_table *pt)
+{
+	struct hsm_irqfd *irqfd;
+
+	irqfd = container_of(pt, struct hsm_irqfd, pt);
+	add_wait_queue(wqh, &irqfd->wait);
+}
+
+/*
+ * Assign an eventfd to a VM and create a HSM irqfd associated with the
+ * eventfd. The properties of the HSM irqfd are built from a &struct
+ * acrn_irqfd.
+ */
+static int acrn_irqfd_assign(struct acrn_vm *vm, struct acrn_irqfd *args)
+{
+	struct eventfd_ctx *eventfd = NULL;
+	struct hsm_irqfd *irqfd, *tmp;
+	__poll_t events;
+	int ret = 0;
+
+	irqfd = kzalloc_obj(*irqfd);
+	if (!irqfd)
+		return -ENOMEM;
+
+	irqfd->vm = vm;
+	memcpy(&irqfd->msi, &args->msi, sizeof(args->msi));
+	INIT_LIST_HEAD(&irqfd->list);
+	INIT_WORK(&irqfd->shutdown, hsm_irqfd_shutdown_work);
+
+	CLASS(fd, f)(args->fd);
+	if (fd_empty(f)) {
+		ret = -EBADF;
+		goto out;
+	}
+
+	eventfd = eventfd_ctx_fileget(fd_file(f));
+	if (IS_ERR(eventfd)) {
+		ret = PTR_ERR(eventfd);
+		goto out;
+	}
+
+	irqfd->eventfd = eventfd;
+
+	/*
+	 * Install custom wake-up handling to be notified whenever underlying
+	 * eventfd is signaled.
+	 */
+	init_waitqueue_func_entry(&irqfd->wait, hsm_irqfd_wakeup);
+	init_poll_funcptr(&irqfd->pt, hsm_irqfd_poll_func);
+
+	/*
+	 * Hold irqfds_lock across waitqueue install and list_add so the
+	 * irqfd is not visible to deassign/deinit before its waitqueue
+	 * entry is in place, and any racing EPOLLHUP cleanup work blocks
+	 * on irqfds_lock until publication completes.
+	 */
+	mutex_lock(&vm->irqfds_lock);
+	list_for_each_entry(tmp, &vm->irqfds, list) {
+		if (irqfd->eventfd != tmp->eventfd)
+			continue;
+		ret = -EBUSY;
+		mutex_unlock(&vm->irqfds_lock);
+		goto fail;
+	}
+
+	events = vfs_poll(fd_file(f), &irqfd->pt);
+	list_add_tail(&irqfd->list, &vm->irqfds);
+	if (events & EPOLLIN)
+		acrn_irqfd_inject(irqfd);
+	mutex_unlock(&vm->irqfds_lock);
+
+	return 0;
+fail:
+	eventfd_ctx_put(eventfd);
+out:
+	kfree(irqfd);
+	return ret;
+}
+
+static int acrn_irqfd_deassign(struct acrn_vm *vm,
+			       struct acrn_irqfd *args)
+{
+	struct hsm_irqfd *irqfd, *tmp;
+	struct eventfd_ctx *eventfd;
+
+	eventfd = eventfd_ctx_fdget(args->fd);
+	if (IS_ERR(eventfd))
+		return PTR_ERR(eventfd);
+
+	mutex_lock(&vm->irqfds_lock);
+	list_for_each_entry_safe(irqfd, tmp, &vm->irqfds, list) {
+		if (irqfd->eventfd == eventfd) {
+			list_del_init(&irqfd->list);
+			hsm_irqfd_queue_shutdown(irqfd);
+			break;
+		}
+	}
+	mutex_unlock(&vm->irqfds_lock);
+	eventfd_ctx_put(eventfd);
+
+	/* Wait for cleanup work to finish so the eventfd is fully detached. */
+	flush_workqueue(vm->irqfd_wq);
+
+	return 0;
+}
+
+int acrn_irqfd_config(struct acrn_vm *vm, struct acrn_irqfd *args)
+{
+	int ret;
+
+	if (args->flags & ACRN_IRQFD_FLAG_DEASSIGN)
+		ret = acrn_irqfd_deassign(vm, args);
+	else
+		ret = acrn_irqfd_assign(vm, args);
+
+	return ret;
+}
+
+int acrn_irqfd_init(struct acrn_vm *vm)
+{
+	INIT_LIST_HEAD(&vm->irqfds);
+	mutex_init(&vm->irqfds_lock);
+	vm->irqfd_wq = alloc_workqueue("acrn_irqfd-%u", WQ_PERCPU, 0, vm->vmid);
+	if (!vm->irqfd_wq)
+		return -ENOMEM;
+
+	dev_dbg(acrn_dev.this_device, "VM %u irqfd init.\n", vm->vmid);
+	return 0;
+}
+
+void acrn_irqfd_deinit(struct acrn_vm *vm)
+{
+	struct hsm_irqfd *irqfd, *next;
+
+	dev_dbg(acrn_dev.this_device, "VM %u irqfd deinit.\n", vm->vmid);
+
+	mutex_lock(&vm->irqfds_lock);
+	list_for_each_entry_safe(irqfd, next, &vm->irqfds, list) {
+		list_del_init(&irqfd->list);
+		hsm_irqfd_queue_shutdown(irqfd);
+	}
+	mutex_unlock(&vm->irqfds_lock);
+
+	/* Drain all cleanup work before tearing the workqueue down. */
+	flush_workqueue(vm->irqfd_wq);
+	destroy_workqueue(vm->irqfd_wq);
+}