Re: [PATCH net] nfp: fix rcu_read_lock/unlock while rcu_derefrencing

[Leon Romanovsky <leon@kernel.org>]

On Tue, May 09, 2023 at 08:06:32AM +0200, Louis Peens wrote:
> From: Tianyu Yuan <tianyu.yuan@corigine.com>
> 
> When CONFIG_PROVE_LOCKING and CONFIG_PROVE_RCU are enabled, using
> OVS with vf reprs on bridge will lead to following log in dmesg:
> 
> '''
>  .../nfp/flower/main.c:269 suspicious rcu_dereference_check() usage!
> 
>  other info that might help us debug this:
> 
>  rcu_scheduler_active = 2, debug_locks = 1
>  no locks held by swapper/15/0.
> 
>  ......
>  Call Trace:
>   <IRQ>
>   dump_stack_lvl+0x8c/0xa0
>   lockdep_rcu_suspicious+0x118/0x1a0
>   nfp_flower_dev_get+0xc1/0x240 [nfp]
>   nfp_nfd3_rx+0x419/0xb90 [nfp]
>   ? validate_chain+0x640/0x1880
>   nfp_nfd3_poll+0x3e/0x180 [nfp]
>   __napi_poll+0x28/0x1d0
>   net_rx_action+0x2bd/0x3c0
>   ? _raw_spin_unlock_irqrestore+0x42/0x70
>   __do_softirq+0xc3/0x3c6
>   irq_exit_rcu+0xeb/0x130
>   common_interrupt+0xb9/0xd0
>   </IRQ>
>   <TASK>
>   ......
>   </TASK>
> '''
> 
> This debug log is caused by missing of rcu_read_lock()/unlock().
> In previous patch rcu_read_lock/unlock are removed while they are
> still needed when calling rcu_dereference() in nfp_app_dev_get().
> 
> Fixes: d5789621b658 ("nfp: Remove rcu_read_lock() around XDP program invocation")
> CC: stable@vger.kernel.org
> Signed-off-by: Tianyu Yuan <tianyu.yuan@corigine.com>
> Acked-by: Simon Horman <simon.horman@corigine.com>
> Signed-off-by: Louis Peens <louis.peens@corigine.com>
> ---
>  drivers/net/ethernet/netronome/nfp/nfd3/dp.c  |  4 ++--
>  drivers/net/ethernet/netronome/nfp/nfd3/xsk.c |  2 +-
>  drivers/net/ethernet/netronome/nfp/nfdk/dp.c  |  4 ++--
>  drivers/net/ethernet/netronome/nfp/nfp_app.h  | 16 ++++++++++++++++
>  4 files changed, 21 insertions(+), 5 deletions(-)
> 

Thanks,
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>