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Message-ID: <2e87058c-839b-5b28-62e1-896d1e49fb57@broadcom.com>
Date: Wed, 19 Jul 2023 11:17:14 -0700
From: Scott Branden <scott.branden@...adcom.com>
To: Ray Jui <ray.jui@...adcom.com>,
Chengfeng Ye <dg573847474@...il.com>,
bcm-kernel-feedback-list@...adcom.com, arnd@...db.de,
gregkh@...uxfoundation.org
Cc: linux-kernel@...r.kernel.org, desmond.yan@...adcom.com
Subject: Re: [PATCH v3] misc: bcm_vk: Fix potential deadlock on &vk->ctx_lock
On 2023-07-19 10:31, Ray Jui wrote:
>
>
> On 7/19/2023 10:07 AM, Scott Branden wrote:
>> Works fine - thanks.
>
> So apparently the choice of using the timer previously was not due to
> performance reasons?
Correct - the heartbeat does not need high performance.
>
> If performance is a concern by converting to use workqueue (now it runs
> in process/thread context than softirq), I assume you are aware of
> another easy way to fix this potential deadlock issue? :)
Performance not a concern.
>>
>> 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@...il.com>
>> Acked-by: Scott Branden <scott.branden@...adcom.com>
>> Tested-by: Desmond Yan <desmond.branden@...adcom.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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