netdev - Re: [PATCH] net: Fix xps_needed inc/dec mismatch

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Date:   Fri, 7 Dec 2018 15:15:49 +0000
From:   Ross Lagerwall <ross.lagerwall@...rix.com>
To:     Sabrina Dubroca <sd@...asysnail.net>
CC:     <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>,
        Amritha Nambiar <amritha.nambiar@...el.com>
Subject: Re: [PATCH] net: Fix xps_needed inc/dec mismatch

On 12/7/18 11:01 AM, Sabrina Dubroca wrote:
> Hi Ross,
> 
> 2018-12-07, 10:16:21 +0000, Ross Lagerwall wrote:
>> xps_needed is incremented only when a new dev map is allocated (in
>> __netif_set_xps_queue). Therefore it should be decremented only when we
>> actually have a dev map to destroy. Without this, it may be decremented
>> too many times which causes netif_reset_xps_queues to return early and
>> not actually clean up the old dev maps. This results in a crash in
>> __netif_set_xps_queue when it is called later.
>>
>> The crash occurred when having multiple ixgbe devices in a host. lldpad
>> would reconfigure them to be FCoE-capable causing reset_xps_queues /
>> set_xps_queue to be called several times. The xps_needed count would get
>> out of sync and eventually the above-mentioned crash would occur.
>>
>> Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
> 
> I posted another patchset recently (commits f28c020fb488 and
> 867d0ad476db in the "net" tree) for issues in XPS, including broken
> xps_needed accounting, so your patch won't apply to David's "net"
> tree. Could you try it with your use case, and if you still see
> issues, fix them on top? You can grab the latest net tree here:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git
> 

Your two commits fix the issue I was seeing. Thanks!

-- 
Ross Lagerwall