From: sashiko-bot@kernel.org
To: "Dapeng Mi" <dapeng1.mi@linux.intel.com>
Cc: linux-perf-users@vger.kernel.org
Subject: Re: [Patch v5 18/18] perf/core: Don't overwrite shared LBR stack depth
Date: Thu, 29 Oct 2026 04:57:38 +0000 [thread overview]
Message-ID: <sashiko-outbox-188719@kernel.org> (raw)
In-Reply-To: <20261029043914.1395147-19-dapeng1.mi@linux.intel.com>
> perf_sample_save_brstack() currently clamps the shared LBR stack depth
> to min(event->attr.sample_max_stack, brs->nr). This is unsafe because
> the global LBR stack is shared across all LBR events, and a small
> sample_max_stack from one event can shrink the depth for all others in
> the same PMI.
>
> As a result, later events may output a shorter LBR stack than requested
> even when they do not require a small sample depth. Do not overwrite the
> shared LBR stack depth in perf_sample_save_brstack(); instead, keep the
> per-event limit in a local variable so each event is constrained
> independently without mutating global state.
>
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Fixes: c53e14f1ea4a ("perf: Extend per event callchain limit to branch stack")
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Sashiko has reviewed this patch and found no issues.
--
Sashiko AI review · https://sashiko.dev/#/patchset/20261029043914.1395147-1-dapeng1.mi@linux.intel.com?part=18
prev parent reply other threads:[~2026-10-29 4:57 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-29 4:38 [Patch v5 00/18] perf/x86: Fix multiple LBR sampling issues Dapeng Mi
2026-10-29 4:38 ` [Patch v5 01/18] perf/x86: Disable LBR if x86_pmu.lbr_nr exceeds MAX_LBR_ENTRIES Dapeng Mi
2026-10-29 5:03 ` sashiko-bot
2026-10-29 9:38 ` Peter Zijlstra
2026-10-29 9:56 ` Mi, Dapeng
2026-10-29 10:19 ` Peter Zijlstra
2026-10-29 4:38 ` [Patch v5 02/18] perf/x86/intel: Validate LBR XSAVE state before updating LBR stack Dapeng Mi
2026-10-29 5:11 ` sashiko-bot
2026-10-29 9:40 ` Peter Zijlstra
2026-10-29 10:09 ` Mi, Dapeng
2026-10-29 4:38 ` [Patch v5 03/18] perf/x86/amd/lbr: Limit branch snapshots to valid entries Dapeng Mi
2026-10-29 4:53 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 04/18] perf/x86/intel/lbr: " Dapeng Mi
2026-10-29 4:56 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 05/18] perf/x86: Add lbr_enabled to track LBR state Dapeng Mi
2026-10-29 5:10 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 06/18] perf/x86/amd: Avoid re-enabling PMU and LBR for BPF when disabled Dapeng Mi
2026-10-29 5:08 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 07/18] perf/x86/intel: Add helper to enable PMU without LBR Dapeng Mi
2026-10-29 4:51 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 08/18] perf/x86/intel: Avoid re-enabling PMU and LBR for BPF when disabled Dapeng Mi
2026-10-29 5:02 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 09/18] perf/x86/intel: Keep LBR frozen throughout PMI handling Dapeng Mi
2026-10-29 4:59 ` sashiko-bot
2026-10-29 10:29 ` Peter Zijlstra
2026-10-29 4:39 ` [Patch v5 10/18] perf/x86/intel: Allow LBR read helpers to operate on explicit stacks Dapeng Mi
2026-10-29 4:58 ` sashiko-bot
2026-10-29 10:38 ` Peter Zijlstra
2026-10-29 4:39 ` [Patch v5 11/18] perf/x86/intel: Use a dedicated LBR stack for BPF snapshotting Dapeng Mi
2026-10-29 5:05 ` sashiko-bot
2026-10-29 10:41 ` Peter Zijlstra
2026-10-29 4:39 ` [Patch v5 12/18] perf/x86/intel: Always snapshot live hardware LBR state for BPF Dapeng Mi
2026-10-29 5:01 ` sashiko-bot
2026-10-29 10:56 ` Peter Zijlstra
2026-10-29 4:39 ` [Patch v5 13/18] perf/x86/intel: Refresh LBR stack for non-PEBS LBR events if needed Dapeng Mi
2026-10-29 5:09 ` sashiko-bot
2026-10-29 11:00 ` Peter Zijlstra
2026-10-29 4:39 ` [Patch v5 14/18] perf/x86/intel: Account arch-PEBS in lbr_pebs_users Dapeng Mi
2026-10-29 4:55 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 15/18] perf/x86/intel: Clear raw LBR counters in the LBR stack Dapeng Mi
2026-10-29 5:03 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 16/18] perf/x86/intel: Refill LBR stack for LBR counter events in PMI handler Dapeng Mi
2026-10-29 5:16 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 17/18] perf/x86/intel: Pass LBR stack size into store_lbr() Dapeng Mi
2026-10-29 4:53 ` sashiko-bot
2026-10-29 4:39 ` [Patch v5 18/18] perf/core: Don't overwrite shared LBR stack depth Dapeng Mi
2026-10-29 4:57 ` sashiko-bot [this message]
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