[BUG] net: mellanox: mlx4: possible deadlock in mlx4_xdp_set() and mlx4_en_reset_config()

[Jia-Ju Bai]

Hello,

My static analysis tool reports a possible deadlock in the mlx4 driver 
in Linux 5.16:

mlx4_xdp_set()
  mutex_lock(&mdev->state_lock); --> Line 2778 (Lock A)
  mlx4_en_try_alloc_resources()
    mlx4_en_alloc_resources()
      mlx4_en_destroy_tx_ring()
        mlx4_qp_free()
          wait_for_completion(&qp->free); --> Line 528 (Wait X)

mlx4_en_reset_config()
  mutex_lock(&mdev->state_lock); --> Line 3522 (Lock A)
  mlx4_en_try_alloc_resources()
    mlx4_en_alloc_resources()
      mlx4_en_destroy_tx_ring()
        mlx4_qp_free()
          complete(&qp->free); --> Line 527 (Wake X)

When mlx4_xdp_set() is executed, "Wait X" is performed by holding "Lock 
A". If mlx4_en_reset_config() is executed at this time, "Wake X" cannot 
be performed to wake up "Wait X" in mlx4_xdp_set(), because "Lock A" has 
been already hold by mlx4_xdp_set(), causing a possible deadlock.

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


Best wishes,
Jia-Ju Bai