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