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

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Message-ID: <20250122172235.GG3436806@ragnatech.se>
Date: Wed, 22 Jan 2025 18:22:35 +0100
From: Niklas Söderlund <niklas.soderlund@...natech.se>
To: Kory Maincent <kory.maincent@...tlin.com>
Cc: Paul Barker <paul.barker.ct@...renesas.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Mikhail Ulyanov <mikhail.ulyanov@...entembedded.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
	netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/2] net: ravb: Fix missing rtnl lock in suspend path

Hi Kory,

Thanks for your work.

On 2025-01-22 17:19:28 +0100, 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@...renesas.com>
> Closes: https://lore.kernel.org/netdev/4c6419d8-c06b-495c-b987-d66c2e1ff848@tuxon.dev/
> Fixes: 0184165b2f42 ("ravb: add sleep PM suspend/resume support")
> Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>

I need to apply [1] to see the WARNING: suspicious RCU usage splat at 
all, I guess there is a WARN_ONCE somewhere. But with this patch applied 
the splat is gone when resuming and WoL works.

Tested on R-Car M3N with NFS root on the interface used for WoL.

Tested-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>

1. [PATCH] gpio: rcar: Use raw_spinlock to protect register access

> ---
>  drivers/net/ethernet/renesas/ravb_main.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index bc395294a32d..2c6d8e4966c3 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -3217,10 +3217,15 @@ static int ravb_suspend(struct device *dev)
>  
>  	netif_device_detach(ndev);
>  
> -	if (priv->wol_enabled)
> -		return ravb_wol_setup(ndev);
> +	rtnl_lock();
> +	if (priv->wol_enabled) {
> +		ret = ravb_wol_setup(ndev);
> +		rtnl_unlock();
> +		return ret;
> +	}
>  
>  	ret = ravb_close(ndev);
> +	rtnl_unlock();
>  	if (ret)
>  		return ret;
>  
> @@ -3245,19 +3250,25 @@ static int ravb_resume(struct device *dev)
>  	if (!netif_running(ndev))
>  		return 0;
>  
> +	rtnl_lock();
>  	/* If WoL is enabled restore the interface. */
>  	if (priv->wol_enabled) {
>  		ret = ravb_wol_restore(ndev);
> -		if (ret)
> +		if (ret)  {
> +			rtnl_unlock();
>  			return ret;
> +		}
>  	} else {
>  		ret = pm_runtime_force_resume(dev);
> -		if (ret)
> +		if (ret) {
> +			rtnl_unlock();
>  			return ret;
> +		}
>  	}
>  
>  	/* Reopening the interface will restore the device to the working state. */
>  	ret = ravb_open(ndev);
> +	rtnl_unlock();
>  	if (ret < 0)
>  		goto out_rpm_put;
>  
> 
> -- 
> 2.34.1
> 

-- 
Kind Regards,
Niklas Söderlund