netdev - Re: [PATCH net-next v7 3/7] net: stmmac: refactor FPE verification process

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Message-ID: <20240904145837.wh7tdrffsiqpot22@skbuf>
Date: Wed, 4 Sep 2024 17:58:37 +0300
From: Vladimir Oltean <olteanv@...il.com>
To: Furong Xu <0x1207@...il.com>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>,
	Serge Semin <fancer.lancer@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Joao Pinto <jpinto@...opsys.com>, netdev@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	rmk+kernel@...linux.org.uk, linux@...linux.org.uk, xfr@...look.com,
	Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next v7 3/7] net: stmmac: refactor FPE verification
 process

On Wed, Sep 04, 2024 at 05:21:18PM +0800, Furong Xu wrote:
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 3072ad33b105..e2f933353f40 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -969,17 +969,30 @@ static void stmmac_mac_config(struct phylink_config *config, unsigned int mode,
>  static void stmmac_fpe_link_state_handle(struct stmmac_priv *priv, bool is_up)
>  {
>  	struct stmmac_fpe_cfg *fpe_cfg = &priv->fpe_cfg;
> -	enum stmmac_fpe_state *lo_state = &fpe_cfg->lo_fpe_state;
> -	enum stmmac_fpe_state *lp_state = &fpe_cfg->lp_fpe_state;
> -	bool *hs_enable = &fpe_cfg->hs_enable;
> +	unsigned long flags;
>  
> -	if (is_up && *hs_enable) {
> -		stmmac_fpe_send_mpacket(priv, priv->ioaddr, fpe_cfg,
> -					MPACKET_VERIFY);
> +	del_timer_sync(&fpe_cfg->verify_timer);

Interesting comments in include/linux/timer.h:
 * Do not use in new code. Use timer_delete_sync() instead.

Also, interesting comment in the timer_delete_sync() kernel-doc:
 Callers must prevent restarting of the timer, otherwise this function is meaningless.

I don't think you have any restart prevention mechanism. So between the
timer deletion and the spin_lock_irqsave(), another thread has enough
time to acquire fpe_cfg->lock first, and run stmmac_fpe_verify_timer_arm().