netdev - Re: [PATCH net] net: avoid prefetching NULL pointers

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Message-ID: <bd79936a-685a-4509-b01d-a40be0fd6f65@linux.ibm.com>
Date: Fri, 19 Dec 2025 17:41:46 +0530
From: Aditya Gupta <adityag@...ux.ibm.com>
To: Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller"
 <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
        eric.dumazet@...il.com
Subject: Re: [PATCH net] net: avoid prefetching NULL pointers


On 18/12/25 13:48, Eric Dumazet wrote:
> Aditya Gupta reported PowerPC crashes bisected to the blamed commit.
>
> Apparently some platforms do not allow prefetch() on arbitrary pointers.
>
>    prefetch(next);
>    prefetch(&next->priority); // CRASH when next == NULL
>
> Only NULL seems to be supported, with specific handling in prefetch().
>
> Add a conditional to avoid the two prefetches and the skb->next clearing
> for the last skb in the list.
>
> Fixes: b2e9821cff6c ("net: prefech skb->priority in __dev_xmit_skb()")
> Reported-by: Aditya Gupta <adityag@...ux.ibm.com>
> Closes: https://lore.kernel.org/netdev/e9f4abee-b132-440f-a50e-bced0868b5a7@linux.ibm.com/T/#mddc372b64ec5a3b181acc9ee3909110c391cc18a
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>   net/core/dev.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)


Thanks for the quick fix Eric.

It fixes the reported kernel bug, hence:

Tested-by: Aditya Gupta <adityag@...ux.ibm.com>


Thanks,

- Aditya G