linux-kernel - Re: [PATCH v5 bpf-next 1/3] bpf: Add kmem

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Message-ID: <Zwl43rM2X2D4D5z-@google.com>
Date: Fri, 11 Oct 2024 12:13:34 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <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>,
	LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Kees Cook <kees@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v5 bpf-next 1/3] bpf: Add kmem_cache iterator

Hello Alexei,

On Fri, Oct 11, 2024 at 11:33:31AM -0700, Alexei Starovoitov wrote:
> On Thu, Oct 10, 2024 at 4:25 PM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > The new "kmem_cache" iterator will traverse the list of slab caches
> > and call attached BPF programs for each entry.  It should check the
> > argument (ctx.s) if it's NULL before using it.
> >
> > Now the iteration grabs the slab_mutex only if it traverse the list and
> 
> traverses
> 
> > releases the mutex when it runs the BPF program.  The kmem_cache entry
> > is protected by a refcount during the execution.
> >
> > It includes the internal "mm/slab.h" header to access kmem_cache,
> > slab_caches and slab_mutex.  Hope it's ok to mm folks.
> 
> What was the reason you dropped Vlastimil's and Roman's acks
> from this patch while keeping them in patch 2 ?

I wanted to make sure the slab maintainers agree with the refcounting and
the locking logic changes.  But I forgot to add back Vlastimil's Acked
for the v4 which is the same in this regard.

> 
> Folks pls Ack again if it looks ok.
> 
> I'm ready to apply, but would like the acks first.
> 
> Also I'd like to remove the above paragraph
> from mm/slab.h from the commit log.
> It was good to ask during v1, but looks odd at v5.

Sure, feel free to make any changes.

Thanks,
Namhyung