netdev - RE: [EXT] [PATCH net] qede: avoid uninitialized entries in coal

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Date:   Fri, 24 Feb 2023 07:25:00 +0000
From:   Manish Chopra <manishc@...vell.com>
To:     Michal Schmidt <mschmidt@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Ariel Elior <aelior@...vell.com>, Alok Prasad <palok@...vell.com>
Subject: RE: [EXT] [PATCH net] qede: avoid uninitialized entries in coal_entry
 array

> -----Original Message-----
> From: Michal Schmidt <mschmidt@...hat.com>
> Sent: Friday, February 24, 2023 6:12 AM
> To: netdev@...r.kernel.org
> Cc: Manish Chopra <manishc@...vell.com>; Ariel Elior
> <aelior@...vell.com>; Alok Prasad <palok@...vell.com>
> Subject: [EXT] [PATCH net] qede: avoid uninitialized entries in coal_entry array
> 
> External Email
> 
> ----------------------------------------------------------------------
> Even after commit 908d4bb7c54c ("qede: fix interrupt coalescing
> configuration"), some entries of the coal_entry array may theoretically be
> used uninitialized:
> 
>  1. qede_alloc_fp_array() allocates QEDE_MAX_RSS_CNT entries for
>     coal_entry. The initial allocation uses kcalloc, so everything is
>     initialized.
>  2. The user sets a small number of queues (ethtool -L).
>     coal_entry is reallocated for the actual small number of queues.
>  3. The user sets a bigger number of queues.
>     coal_entry is reallocated bigger. The added entries are not
>     necessarily initialized.
> 
> In practice, the reallocations will actually keep using the originally allocated
> region of memory, but we should not rely on it.
> 
> The reallocation is unnecessary. coal_entry can always have
> QEDE_MAX_RSS_CNT entries.

Hi Michal,

Reallocation is necessary here, the motivation for reallocation is commit b0ec5489c480
("qede: preserve per queue stats across up/down of interface"). The coalescing configuration
set from ethtool also needs to be retained across the interface state change, with this change
you are not going to retain anything but always initialize with default. IMO, reallocation will
always try to use same memory which was originally allocated if the requirement fits into it and
which is the case here (driver will not attempt to allocate anything extra which were originally
allocated ever). So there should not be any uninitialized contents, either they will be zero or
something which were configured from ethtool by the user previously.

Nacked-by: Manish Chopra <manishc@...vell.com>

Thanks,
Manish

> 
> Fixes: 908d4bb7c54c ("qede: fix interrupt coalescing configuration")
> Signed-off-by: Michal Schmidt <mschmidt@...hat.com>
> ---
>  drivers/net/ethernet/qlogic/qede/qede_main.c | 21 +++++++-------------
>  1 file changed, 7 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qlogic/qede/qede_main.c
> b/drivers/net/ethernet/qlogic/qede/qede_main.c
> index 4a3c3b5fb4a1..261f982ca40d 100644
> --- a/drivers/net/ethernet/qlogic/qede/qede_main.c
> +++ b/drivers/net/ethernet/qlogic/qede/qede_main.c
> @@ -963,7 +963,6 @@ static int qede_alloc_fp_array(struct qede_dev *edev)
> {
>  	u8 fp_combined, fp_rx = edev->fp_num_rx;
>  	struct qede_fastpath *fp;
> -	void *mem;
>  	int i;
> 
>  	edev->fp_array = kcalloc(QEDE_QUEUE_CNT(edev), @@ -974,20
> +973,14 @@ static int qede_alloc_fp_array(struct qede_dev *edev)
>  	}
> 
>  	if (!edev->coal_entry) {
> -		mem = kcalloc(QEDE_MAX_RSS_CNT(edev),
> -			      sizeof(*edev->coal_entry), GFP_KERNEL);
> -	} else {
> -		mem = krealloc(edev->coal_entry,
> -			       QEDE_QUEUE_CNT(edev) * sizeof(*edev-
> >coal_entry),
> -			       GFP_KERNEL);
> -	}
> -
> -	if (!mem) {
> -		DP_ERR(edev, "coalesce entry allocation failed\n");
> -		kfree(edev->coal_entry);
> -		goto err;
> +		edev->coal_entry = kcalloc(QEDE_MAX_RSS_CNT(edev),
> +					   sizeof(*edev->coal_entry),
> +					   GFP_KERNEL);
> +		if (!edev->coal_entry) {
> +			DP_ERR(edev, "coalesce entry allocation failed\n");
> +			goto err;
> +		}
>  	}
> -	edev->coal_entry = mem;
> 
>  	fp_combined = QEDE_QUEUE_CNT(edev) - fp_rx - edev->fp_num_tx;
> 
> --
> 2.39.1