netdev - Re: [PATCH] ice: Don't use GFP

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Date:   Sun, 16 Jan 2022 22:42:41 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Dave Ertman <david.m.ertman@...el.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org
Subject: Re: [PATCH] ice: Don't use GFP_KERNEL in atomic context

On Sun, Jan 16, 2022 at 07:46:20PM +0100, Christophe JAILLET wrote:
> ice_misc_intr() is an irq handler. It should not sleep.
> 
> Use GFP_ATOMIC instead of GFP_KERNEL when allocating some memory.
> 
> Fixes: 348048e724a0 ("ice: Implement iidc operations")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> I've never played a lot with irq handler. My understanding is that they
> should never sleep.

Hi Christophe

Threaded interrupt handlers are allowed to sleep. However, this
handler is not being used in such a way. So your are probably correct
about GFP_KERNEL vs GFP_ATOMIC. 

> ---
>  drivers/net/ethernet/intel/ice/ice_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
> index 30814435f779..65de01f3a504 100644
> --- a/drivers/net/ethernet/intel/ice/ice_main.c
> +++ b/drivers/net/ethernet/intel/ice/ice_main.c
> @@ -3018,7 +3018,7 @@ static irqreturn_t ice_misc_intr(int __always_unused irq, void *data)
>  		struct iidc_event *event;
>  
>  		ena_mask &= ~ICE_AUX_CRIT_ERR;
> -		event = kzalloc(sizeof(*event), GFP_KERNEL);
> +		event = kzalloc(sizeof(*event), GFP_ATOMIC);
>  		if (event) {
>  			set_bit(IIDC_EVENT_CRIT_ERR, event->type);
>  			/* report the entire OICR value to AUX driver */

What happens next is interesting...


                        event->reg = oicr;
                        ice_send_event_to_aux(pf, event);

where:

void ice_send_event_to_aux(struct ice_pf *pf, struct iidc_event *event)
{
        struct iidc_auxiliary_drv *iadrv;

        if (!pf->adev)
                return;

        device_lock(&pf->adev->dev);
        iadrv = ice_get_auxiliary_drv(pf);
        if (iadrv && iadrv->event_handler)
                iadrv->event_handler(pf, event);
        device_unlock(&pf->adev->dev);
}

device_lock() takes a mutex, not something you should be doing in
atomic context.

So it looks to me, this handler really should be running in thread
context...

	Andrew