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Message-ID: <20210409084436.GK3697@techsingularity.net>
Date: Fri, 9 Apr 2021 09:44:36 +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 Fri, Apr 09, 2021 at 01:33:24AM -0700, Xie He wrote:
> On Fri, Apr 9, 2021 at 12:30 AM Mel Gorman <mgorman@...hsingularity.net> wrote:
> >
> > Under what circumstances do you expect sk_memalloc_socks() to be false
> > and skb_pfmemalloc() to be true that would cause a problem?
>
> For example, if at the time the skb is allocated,
> "sk_memalloc_socks()" was true, then the skb might be allocated as a
> pfmemalloc skb. However, if after this skb is allocated and before
> this skb reaches "__netif_receive_skb", "sk_memalloc_socks()" has
> changed from "true" to "false", then "__netif_receive_skb" will see
> "sk_memalloc_socks()" being false and "skb_pfmemalloc(skb)" being
> true.
>
> This is a problem because this would cause a pfmemalloc skb to be
> delivered to "taps" and protocols that don't support pfmemalloc skbs.
That would imply that the tap was communicating with a swap device to
allocate a pfmemalloc skb which shouldn't happen. Furthermore, it would
require the swap device to be deactivated while pfmemalloc skbs still
existed. Have you encountered this problem?
--
Mel Gorman
SUSE Labs
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