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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Xie He <xie.he.0141@gmail.com>, Mel Gorman <mgorman@techsingularity.net>
Cc: Mel Gorman <mgorman@suse.de>,
	jslaby@suse.cz, Neil Brown <neilb@suse.de>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Mike Christie <michaelc@cs.wisc.edu>,
	Eric B Munson <emunson@mgebm.net>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Sebastian Andrzej Siewior <sebastian@breakpoint.cc>,
	Christoph Lameter <cl@linux.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Linux Kernel Network Developers <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: Problem in pfmemalloc skb handling in net/core/dev.c
Date: Fri, 9 Apr 2021 12:04:11 +0200	[thread overview]
Message-ID: <87ab3d13-f95d-07c5-fc6a-fb33e32685e5@gmail.com> (raw)
In-Reply-To: <CAJht_EPrdujG_0QHM1vc2yrgwwKMQiFzUAK2pgR4dS4z9-Xknw@mail.gmail.com>



On 4/9/21 11:14 AM, Xie He wrote:
> On Fri, Apr 9, 2021 at 1:44 AM Mel Gorman <mgorman@techsingularity.net> wrote:
>>
>> 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?
> 
> I'm not a user of swap devices or pfmemalloc skbs. I just want to make
> sure the protocols that I'm developing (not IP or IPv6) won't get
> pfmemalloc skbs when receiving, because those protocols cannot handle
> them.
> 
> According to the code, it seems always possible to get a pfmemalloc
> skb when a network driver calls "__netdev_alloc_skb". The skb will
> then be queued in per-CPU backlog queues when the driver calls
> "netif_rx". There seems to be nothing preventing "sk_memalloc_socks()"
> from becoming "false" after the skb is allocated and before it is
> handled by "__netif_receive_skb".
> 
> Do you mean that at the time "sk_memalloc_socks()" changes from "true"
> to "false", there would be no in-flight skbs currently being received,
> and all network communications have been paused?
> 


Note that pfmemalloc skbs are normally dropped in sk_filter_trim_cap()

Simply make sure your protocol use it.

  parent reply	other threads:[~2021-04-09 10:15 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-08 18:52 Problem in pfmemalloc skb handling in net/core/dev.c Xie He
2021-04-09  7:30 ` Mel Gorman
2021-04-09  8:33   ` Xie He
2021-04-09  8:44     ` Mel Gorman
2021-04-09  9:14       ` Xie He
2021-04-09  9:58         ` Mel Gorman
2021-04-09 10:08           ` Xie He
2021-04-09 10:04         ` Eric Dumazet [this message]
2021-04-09 10:14           ` Xie He
2021-04-09 11:50             ` Eric Dumazet
2021-04-09 19:12               ` Xie He
2021-04-12 20:40                 ` Xie He

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