linux-kernel - Re: Problem in pfmemalloc skb handling in net/core/dev.c

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Message-ID: <20210409073046.GI3697@techsingularity.net>
Date:   Fri, 9 Apr 2021 08:30:46 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Xie He <xie.he.0141@...il.com>
Cc:     Mel Gorman <mgorman@...e.de>, jslaby@...e.cz,
        Neil Brown <neilb@...e.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Mike Christie <michaelc@...wisc.edu>,
        Eric B Munson <emunson@...bm.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem in pfmemalloc skb handling in net/core/dev.c

On Thu, Apr 08, 2021 at 11:52:01AM -0700, Xie He wrote:
> Hi Mel Gorman,
> 
> I may have found a problem in pfmemalloc skb handling in
> net/core/dev.c. I see there are "if" conditions checking for
> "sk_memalloc_socks() && skb_pfmemalloc(skb)", and when the condition
> is true, the skb is handled specially as a pfmemalloc skb, otherwise
> it is handled as a normal skb.
> 
> However, if "sk_memalloc_socks()" is false and "skb_pfmemalloc(skb)"
> is true, the skb is still handled as a normal skb. Is this correct?

Under what circumstances do you expect sk_memalloc_socks() to be false
and skb_pfmemalloc() to be true that would cause a problem?

-- 
Mel Gorman
SUSE Labs