Re: [PATCH net v2 1/2] net: ravb: Fix missing rtnl lock in suspend path

[Paul Barker <paul.barker.ct@bp.renesas.com>]

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On 23/01/2025 16:58, Kory Maincent wrote:
> Fix the suspend path by ensuring the rtnl lock is held where required.
> Calls to ravb_open, ravb_close and wol operations must be performed under
> the rtnl lock to prevent conflicts with ongoing ndo operations.
> 
> Without this fix, the following warning is triggered:
> [   39.032969] =============================
> [   39.032983] WARNING: suspicious RCU usage
> [   39.033019] -----------------------------
> [   39.033033] drivers/net/phy/phy_device.c:2004 suspicious
> rcu_dereference_protected() usage!
> ...
> [   39.033597] stack backtrace:
> [   39.033613] CPU: 0 UID: 0 PID: 174 Comm: python3 Not tainted
> 6.13.0-rc7-next-20250116-arm64-renesas-00002-g35245dfdc62c #7
> [   39.033623] Hardware name: Renesas SMARC EVK version 2 based on
> r9a08g045s33 (DT)
> [   39.033628] Call trace:
> [   39.033633]  show_stack+0x14/0x1c (C)
> [   39.033652]  dump_stack_lvl+0xb4/0xc4
> [   39.033664]  dump_stack+0x14/0x1c
> [   39.033671]  lockdep_rcu_suspicious+0x16c/0x22c
> [   39.033682]  phy_detach+0x160/0x190
> [   39.033694]  phy_disconnect+0x40/0x54
> [   39.033703]  ravb_close+0x6c/0x1cc
> [   39.033714]  ravb_suspend+0x48/0x120
> [   39.033721]  dpm_run_callback+0x4c/0x14c
> [   39.033731]  device_suspend+0x11c/0x4dc
> [   39.033740]  dpm_suspend+0xdc/0x214
> [   39.033748]  dpm_suspend_start+0x48/0x60
> [   39.033758]  suspend_devices_and_enter+0x124/0x574
> [   39.033769]  pm_suspend+0x1ac/0x274
> [   39.033778]  state_store+0x88/0x124
> [   39.033788]  kobj_attr_store+0x14/0x24
> [   39.033798]  sysfs_kf_write+0x48/0x6c
> [   39.033808]  kernfs_fop_write_iter+0x118/0x1a8
> [   39.033817]  vfs_write+0x27c/0x378
> [   39.033825]  ksys_write+0x64/0xf4
> [   39.033833]  __arm64_sys_write+0x18/0x20
> [   39.033841]  invoke_syscall+0x44/0x104
> [   39.033852]  el0_svc_common.constprop.0+0xb4/0xd4
> [   39.033862]  do_el0_svc+0x18/0x20
> [   39.033870]  el0_svc+0x3c/0xf0
> [   39.033880]  el0t_64_sync_handler+0xc0/0xc4
> [   39.033888]  el0t_64_sync+0x154/0x158
> [   39.041274] ravb 11c30000.ethernet eth0: Link is Down
> 
> Reported-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
> Closes: https://lore.kernel.org/netdev/4c6419d8-c06b-495c-b987-d66c2e1ff848@tuxon.dev/
> Fixes: 0184165b2f42 ("ravb: add sleep PM suspend/resume support")
> Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>
> Tested-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
> Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
> ---
> 
> Changes in v2:
> - Move the rtnl_lock before ravb_wol_setup() and and ravb_wol_restore()
>   instead of before the if condition.
> ---
>  drivers/net/ethernet/renesas/ravb_main.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index bc395294a32d..cfe4f0f364f3 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -3217,10 +3217,16 @@ static int ravb_suspend(struct device *dev)
>  
>  	netif_device_detach(ndev);
>  
> -	if (priv->wol_enabled)
> -		return ravb_wol_setup(ndev);
> +	if (priv->wol_enabled) {
> +		rtnl_lock();
> +		ret = ravb_wol_setup(ndev);
> +		rtnl_unlock();
> +		return ret;
> +	}
>  
> +	rtnl_lock();
>  	ret = ravb_close(ndev);
> +	rtnl_unlock();
>  	if (ret)
>  		return ret;
>  
> @@ -3247,7 +3253,9 @@ static int ravb_resume(struct device *dev)
>  
>  	/* If WoL is enabled restore the interface. */
>  	if (priv->wol_enabled) {
> +		rtnl_lock();
>  		ret = ravb_wol_restore(ndev);
> +		rtnl_unlock();
>  		if (ret)
>  			return ret;
>  	} else {
> @@ -3257,7 +3265,9 @@ static int ravb_resume(struct device *dev)
>  	}
>  
>  	/* Reopening the interface will restore the device to the working state. */
> +	rtnl_lock();
>  	ret = ravb_open(ndev);
> +	rtnl_unlock();
>  	if (ret < 0)
>  		goto out_rpm_put;
>  
> 

Please remove Reviewed-by tags when making changes like this in a
subsequent version of a patch series, this is no longer the patch I
reviewed.

I don't like the multiple lock/unlock calls in each function. I think v1
was better, where we take the lock once in each function and then unlock
when it is no longer needed or when we're about to return.

Thanks,

-- 
Paul Barker

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