2021-11-23 07:55:24

by Jia-Ju Bai

Subject: [BUG] fpga: dfl: possible ABBA deadlock in dfl_fpga_cdev_assign_port() and fme_pr()

Hello,

My static analysis tool reports a possible ABBA deadlock in the dfl
driver in Linux 5.10:

dfl_fpga_cdev_assign_port()
  mutex_lock(&cdev->lock); --> Line 1067 (Lock A)
  mutex_lock(&pdata->lock); --> Line 1624 (Lock B)

fme_pr()
  mutex_lock(&pdata->lock); --> Line 126 (Lock B)
  fpga_region_program_fpga()
    fpga_bridges_enable()
      fpga_bridge_enable()
        fme_bridge_enable_set() --> function pointer via
"bridge->br_ops->enable_set()"
          dfl_fpga_cdev_find_port()
            mutex_lock(&cdev->lock); --> Line 499 (LockA)

When dfl_fpga_cdev_assign_port() and fme_pr() are concurrently executed,
the deadlock can occur.

I am not quite sure whether this possible deadlock is real and how to
fix it if it is real.
Any feedback would be appreciated, thanks

Reported-by: TOTE Robot <[email protected]>


Best wishes,
Jia-Ju Bai

2021-11-24 16:00:07

by Wu Hao

Subject: RE: [BUG] fpga: dfl: possible ABBA deadlock in dfl_fpga_cdev_assign_port() and fme_pr()

>
> dfl_fpga_cdev_assign_port()
>   mutex_lock(&cdev->lock); --> Line 1067 (Lock A)
>   mutex_lock(&pdata->lock); --> Line 1624 (Lock B)

This lock is from port platform device.

>
> fme_pr()
>   mutex_lock(&pdata->lock); --> Line 126 (Lock B)

This lock is from fme platform device.

Actually they are different locks, but yes, maybe we should consider
improving the naming to avoid misunderstanding.

Thanks
Hao

>   fpga_region_program_fpga()
>     fpga_bridges_enable()
>       fpga_bridge_enable()
>         fme_bridge_enable_set() --> function pointer via
> "bridge->br_ops->enable_set()"
>           dfl_fpga_cdev_find_port()
>             mutex_lock(&cdev->lock); --> Line 499 (LockA)
>
> When dfl_fpga_cdev_assign_port() and fme_pr() are concurrently executed,
> the deadlock can occur.
>
> I am not quite sure whether this possible deadlock is real and how to
> fix it if it is real.
> Any feedback would be appreciated, thanks
>
> Reported-by: TOTE Robot <[email protected]>
>
>
> Best wishes,
> Jia-Ju Bai