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Date: Sun, 28 Apr 2024 14:05:47 +0100
From: Simon Horman <horms@kernel.org>
To: Corinna Vinschen <vinschen@redhat.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	intel-wired-lan@lists.osuosl.org,
	Nikolay Aleksandrov <razor@blackwall.org>,
	Jason Xing <kerneljasonxing@gmail.com>,
	Paolo Abeni <pabeni@redhat.com>, Jakub Kicinski <kuba@kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	"David S . Miller" <davem@davemloft.net>,
	Tony Nguyen <anthony.l.nguyen@intel.com>,
	Jesse Brandeburg <jesse.brandeburg@intel.com>
Subject: Re: [PATCH net v2] igb: cope with large MAX_SKB_FRAGS
Message-ID: <20240428130547.GV516117@kernel.org>
References: <20240423134731.918157-1-vinschen@redhat.com>
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In-Reply-To: <20240423134731.918157-1-vinschen@redhat.com>

On Tue, Apr 23, 2024 at 03:47:31PM +0200, Corinna Vinschen wrote:
> From: Paolo Abeni <pabeni@redhat.com>
> 
> Sabrina reports that the igb driver does not cope well with large
> MAX_SKB_FRAG values: setting MAX_SKB_FRAG to 45 causes payload
> corruption on TX.
> 
> An easy reproducer is to run ssh to connect to the machine.  With
> MAX_SKB_FRAGS=17 it works, with MAX_SKB_FRAGS=45 it fails.
> 
> The root cause of the issue is that the driver does not take into
> account properly the (possibly large) shared info size when selecting
> the ring layout, and will try to fit two packets inside the same 4K
> page even when the 1st fraglist will trump over the 2nd head.
> 
> Address the issue forcing the driver to fit a single packet per page,
> leaving there enough room to store the (currently) largest possible
> skb_shared_info.
> 
> Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAG")

nit: The trailing "S" in the subject for the fixes tag seems to have been lost.

Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAGS")

> Reported-by: Jan Tluka <jtluka@redhat.com>
> Reported-by: Jirka Hladky <jhladky@redhat.com>
> Reported-by: Sabrina Dubroca <sd@queasysnail.net>
> Tested-by: Sabrina Dubroca <sd@queasysnail.net>
> Tested-by: Corinna Vinschen <vinschen@redhat.com>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>

...