linux-kernel - Re: [PATCH] bpf: Convert lpm_trie::lock to 'raw_spinlock

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Message-ID: <1ed46394-f065-4e8b-8f37-c450b0c1b3a9@t-8ch.de>
Date: Sat, 16 Nov 2024 17:15:33 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Thomas Gleixner <tglx@...utronix.de>, Kunwu Chan <kunwu.chan@...ux.dev>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eddy Z <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, 
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, clrkwllms@...nel.org, 
	Steven Rostedt <rostedt@...dmis.org>, bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-rt-devel@...ts.linux.dev, syzbot+b506de56cbbb63148c33@...kaller.appspotmail.com, 
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: Re: [PATCH] bpf: Convert lpm_trie::lock to 'raw_spinlock_t'

On 2024-11-16 08:01:49-0800, Alexei Starovoitov wrote:
> On Sat, Nov 16, 2024 at 1:21 AM Sebastian Andrzej Siewior
> <bigeasy@...utronix.de> wrote:
> >
> > On 2024-11-15 23:29:31 [+0100], Thomas Gleixner wrote:
> > > IIRC, BPF has it's own allocator which can be used everywhere.
> >
> > Thomas Weißschuh made something. It appears to work. Need to take a
> > closer look.
> 
> Any more details?
> bpf_mem_alloc is a stop gap.

It is indeed using bpf_mem_alloc.
It is a fairly straightforward conversion, using one cache for
intermediate and one for non-intermediate nodes.

I'll try to send it early next week.

> As Vlastimil Babka suggested long ago:
> https://lwn.net/Articles/974138/
> "...next on the target list is the special allocator used by the BPF
> subsystem. This allocator is intended to succeed in any calling
> context, including in non-maskable interrupts (NMIs). BPF maintainer
> Alexei Starovoitov is evidently in favor of this removal if SLUB is
> able to handle the same use cases..."
> 
> Here is the first step:
> https://lore.kernel.org/bpf/20241116014854.55141-1-alexei.starovoitov@gmail.com/