Re: [PATCH v3] misc: bcm_vk: Fix potential deadlock on &vk->ctx_lock

[Scott Branden <scott.branden@broadcom.com>]

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Hi Chengfeng,

Thanks for the work on this.  We need some time to review and test.

On 2023-06-29 11:29, Chengfeng Ye wrote:
> 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 <dg573847474@gmail.com>
> ---
>   drivers/misc/bcm-vk/bcm_vk.h     |  2 +-
>   drivers/misc/bcm-vk/bcm_vk_msg.c | 14 +++++++-------
>   2 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/misc/bcm-vk/bcm_vk.h b/drivers/misc/bcm-vk/bcm_vk.h
> index 25d51222eedf..386884c2a263 100644
> --- a/drivers/misc/bcm-vk/bcm_vk.h
> +++ b/drivers/misc/bcm-vk/bcm_vk.h
> @@ -340,7 +340,7 @@ struct bcm_vk_proc_mon_info {
>   };
>   
>   struct bcm_vk_hb_ctrl {
> -	struct timer_list timer;
> +	struct delayed_work work;
>   	u32 last_uptime;
>   	u32 lost_cnt;
>   };
> diff --git a/drivers/misc/bcm-vk/bcm_vk_msg.c b/drivers/misc/bcm-vk/bcm_vk_msg.c
> index 3c081504f38c..e17d81231ea6 100644
> --- a/drivers/misc/bcm-vk/bcm_vk_msg.c
> +++ b/drivers/misc/bcm-vk/bcm_vk_msg.c
> @@ -137,11 +137,11 @@ void bcm_vk_set_host_alert(struct bcm_vk *vk, u32 bit_mask)
>   #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()) {
> @@ -177,22 +177,22 @@ static void bcm_vk_hb_poll(struct timer_list *t)
>   		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,

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