Re: [PATCH v2] misc: bcm_vk: Fix potential deadlock on &vk->ctx_lock

[Arnd Bergmann]

On Wed, Jun 28, 2023, at 13:29, 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.

The timer function does not seem to be performance critical at all,
it might be nicer to just move it into process context using
a delayed workqueue instead of a timer.

     Arnd