linux-kernel - Re: [PATCH] perf lock contention: Do not use BPF task local storage

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Date:   Wed, 23 Nov 2022 10:49:54 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Martin KaFai Lau <martin.lau@...ux.dev>
Cc:     Namhyung Kim <namhyung@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Song Liu <song@...nel.org>,
        bpf@...r.kernel.org, Blake Jones <blakejones@...gle.com>,
        Chris Li <chriscli@...gle.com>, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH] perf lock contention: Do not use BPF task local storage

Em Mon, Nov 21, 2022 at 09:32:56AM -0800, Martin KaFai Lau escreveu:
> On 11/18/22 11:01 AM, Namhyung Kim wrote:
> > It caused some troubles when a lock inside kmalloc is contended
> > because task local storage would allocate memory using kmalloc.
> > It'd create a recusion and even crash in my system.
> > 
> > There could be a couple of workarounds but I think the simplest
> > one is to use a pre-allocated hash map.
> 
> Acked-by: Martin KaFai Lau <martin.lau@...nel.org>

Thanks, applied.

- Arnaldo

 
> > We could fix the task local storage to use the safe BPF allocator,
> > but it takes time so let's change this until it happens actually.
> 
> I also got another report on the kfree_rcu path.  I am also looking into
> this direction on using the BPF allocator.

-- 

- Arnaldo