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

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Message-ID: <dea8c3c5-0739-58c1-9a88-b989878a9b8f@linux.dev>
Date:   Mon, 21 Nov 2022 09:32:56 -0800
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     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>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH] perf lock contention: Do not use BPF task local storage

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>

> 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.