misc: bcm_vk: Fix potential deadlock on &vk->ctx_lock

As &vk->ctx_lock is acquired by timer bcm_vk_hb_poll() under softirq
context, other process context code should disable irq or bottom-half
before acquire the same lock, otherwise deadlock could happen if the
timer preempt the execution while the lock is held in process context
on the same CPU.

Possible deadlock scenario
bcm_vk_open()
-> bcm_vk_get_ctx()
-> spin_lock(&vk->ctx_lock)
<timer iterrupt>
-> bcm_vk_hb_poll()
-> bcm_vk_blk_drv_access()
-> spin_lock_irqsave(&vk->ctx_lock, flags) (deadlock here)

This flaw was found using an experimental static analysis tool we are
developing for irq-related deadlock, which reported the following
warning when analyzing the linux kernel 6.4-rc7 release.

[Deadlock]: &vk->ctx_lock
[Interrupt]: bcm_vk_hb_poll
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_msg.c:176
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_dev.c:512
[Locking Unit]: bcm_vk_ioctl
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_dev.c:1181
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_dev.c:512

[Deadlock]: &vk->ctx_lock
[Interrupt]: bcm_vk_hb_poll
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_msg.c:176
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_dev.c:512
[Locking Unit]: bcm_vk_ioctl
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_dev.c:1169

[Deadlock]: &vk->ctx_lock
[Interrupt]: bcm_vk_hb_poll
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_msg.c:176
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_dev.c:512
[Locking Unit]: bcm_vk_open
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_msg.c:216

[Deadlock]: &vk->ctx_lock
[Interrupt]: bcm_vk_hb_poll
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_msg.c:176
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_dev.c:512
[Locking Unit]: bcm_vk_release
-->/root/linux/drivers/misc/bcm-vk/bcm_vk_msg.c:306

As suggested by Arnd, the tentative patch fix the potential deadlocks
by replacing the timer with delay workqueue. x86_64 allyesconfig using
GCC shows no new warning. Note that no runtime testing was performed
due to no device on hand.

Signed-off-by: Chengfeng Ye <[e-mail]>
Acked-by: Scott Branden <[e-mail]>
Tested-by: Desmond Yan <[e-mail]>
Tested-by: Desmond Yan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/bcm-vk/bcm_vk.h

···
 };
 
 struct bcm_vk_hb_ctrl {
-	struct timer_list timer;
+	struct delayed_work work;
 	u32 last_uptime;
 	u32 lost_cnt;
 };

drivers/misc/bcm-vk/bcm_vk_msg.c

···
 #define BCM_VK_HB_TIMER_VALUE (BCM_VK_HB_TIMER_S * HZ)
 #define BCM_VK_HB_LOST_MAX (27 / BCM_VK_HB_TIMER_S)
 
-static void bcm_vk_hb_poll(struct timer_list *t)
+static void bcm_vk_hb_poll(struct work_struct *work)
 {
 	u32 uptime_s;
-	struct bcm_vk_hb_ctrl *hb = container_of(t, struct bcm_vk_hb_ctrl,
-						 timer);
+	struct bcm_vk_hb_ctrl *hb = container_of(to_delayed_work(work), struct bcm_vk_hb_ctrl,
+						 work);
 	struct bcm_vk *vk = container_of(hb, struct bcm_vk, hb_ctrl);
 
 	if (bcm_vk_drv_access_ok(vk) && hb_mon_is_on()) {
···
 		bcm_vk_set_host_alert(vk, ERR_LOG_HOST_HB_FAIL);
 	}
 	/* re-arm timer */
-	mod_timer(&hb->timer, jiffies + BCM_VK_HB_TIMER_VALUE);
+	schedule_delayed_work(&hb->work, BCM_VK_HB_TIMER_VALUE);
 }
 
 void bcm_vk_hb_init(struct bcm_vk *vk)
 {
 	struct bcm_vk_hb_ctrl *hb = &vk->hb_ctrl;
 
-	timer_setup(&hb->timer, bcm_vk_hb_poll, 0);
-	mod_timer(&hb->timer, jiffies + BCM_VK_HB_TIMER_VALUE);
+	INIT_DELAYED_WORK(&hb->work, bcm_vk_hb_poll);
+	schedule_delayed_work(&hb->work, BCM_VK_HB_TIMER_VALUE);
 }
 
 void bcm_vk_hb_deinit(struct bcm_vk *vk)
 {
 	struct bcm_vk_hb_ctrl *hb = &vk->hb_ctrl;
 
-	del_timer(&hb->timer);
+	cancel_delayed_work_sync(&hb->work);
 }
 
 static void bcm_vk_msgid_bitmap_clear(struct bcm_vk *vk,