linux-kernel - Re: [PATCH bpf-next v6 2/2] bpf: Hold the perf callchain entry until used completely

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Message-ID: <c41372ad-1591-4f2b-a786-bc0e19f8425c@linux.dev>
Date: Thu, 13 Nov 2025 08:01:38 -0800
From: Yonghong Song <yonghong.song@...ux.dev>
To: Tao Chen <chen.dylane@...ux.dev>, peterz@...radead.org, mingo@...hat.com,
 acme@...nel.org, namhyung@...nel.org, mark.rutland@....com,
 alexander.shishkin@...ux.intel.com, jolsa@...nel.org, irogers@...gle.com,
 adrian.hunter@...el.com, kan.liang@...ux.intel.com
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v6 2/2] bpf: Hold the perf callchain entry until
 used completely



On 11/12/25 8:31 AM, Tao Chen wrote:
> As Alexei noted, get_perf_callchain() return values may be reused
> if a task is preempted after the BPF program enters migrate disable
> mode. The perf_callchain_entres has a small stack of entries, and
> we can reuse it as follows:
>
> 1. get the perf callchain entry
> 2. BPF use...
> 3. put the perf callchain entry
>
> And Peter suggested that get_recursion_context used with preemption
> disabled, so we should disable preemption at BPF side.
>
> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>

Acked-by: Yonghong Song <yonghong.song@...ux.dev>