From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CBC46C3600C for ; Mon, 31 Mar 2025 14:40:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=k7HAqjeWwLVnuthJm9T0TyotQsYdYi4nXf0ltHZaJaY=; b=xKsCCrEQkFTLfETgmT26nYFUmw HxWDxzLpPEIzoKwmJR1gay3gpo6XzSqyt4CcJF1+ANm9X7J+M865oQnCSw3d7ORst7PqDKoF8uaDl 2RKf1me3jK8KdZi4X1j9Me8Tu+qYL/E1eBbUJay0XEflidUsCeQEkmIjVyZDh4QwKGktUl6LhjFVv Lpto7nVwtMFd9GsA0UTgXR5G/tuPqwmUfG7QChRa1XSqV/zGqQY7RnIIHaiZ3Mh1RFL6k46n1b02L gY+3cTL8hLCabKlX3GpEjD7vSXjAWPZmfDD1LxiSmZn1evGr7sgajlCV0XyaQkJkFHMeANVIfR921 YwhwvBKQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.1 #2 (Red Hat Linux)) id 1tzGIw-00000000b3J-0lF7; Mon, 31 Mar 2025 14:39:58 +0000 Received: from tor.source.kernel.org ([172.105.4.254]) by bombadil.infradead.org with esmtps (Exim 4.98.1 #2 (Red Hat Linux)) id 1tzGDg-00000000ZTA-1AHl for linux-arm-kernel@lists.infradead.org; Mon, 31 Mar 2025 14:34:32 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 27DF761126; Mon, 31 Mar 2025 14:34:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 47538C4CEE4; Mon, 31 Mar 2025 14:34:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743431671; bh=RxXN5ImDkHlxqQmfInHiKTyFOrz987IzeR6333NbSJ8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UJzFj0Fb9JehsWcz7uSbYD3tnPXbjTintoKWN9Jb44fNCWgRm/Jl9Ym+tNrx2BqDH medr5Es0YT05yng3VHeBg5vtfcTOcx+g6f2jp3a4dJgIMinDXDRCqa687RQcK8U+y0 0e16qgimqzEnxPk7r0W58IK5KF20wMWzAk5bAvU4OFUeUAW10yA2rkCgBVEqvOgK0H UdRLL/GMIcooyU6qKQ2jtfvXpN6stJX2U+VcOB7t1h4kA9GzPPn1ZmoinaIhqnwZKs Z64XpqFRBkjYbcGGpFEGNWgsj2DwoYNK4fM10l2NQNscMrFWn6s30ax0jqeIhGLH/1 QpltbptrgswnQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Mark Rutland , Rob Herring , Anshuman Khandual , James Clark , Will Deacon , Sasha Levin , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org Subject: [PATCH AUTOSEL 6.14 08/18] perf: arm_pmu: Don't disable counter in armpmu_add() Date: Mon, 31 Mar 2025 10:33:58 -0400 Message-Id: <20250331143409.1682789-8-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250331143409.1682789-1-sashal@kernel.org> References: <20250331143409.1682789-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.14 Content-Transfer-Encoding: 8bit X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Mark Rutland [ Upstream commit dcca27bc1eccb9abc2552aab950b18a9742fb8e7 ] Currently armpmu_add() tries to handle a newly-allocated counter having a stale associated event, but this should not be possible, and if this were to happen the current mitigation is insufficient and potentially expensive. It would be better to warn if we encounter the impossible case. Calls to pmu::add() and pmu::del() are serialized by the core perf code, and armpmu_del() clears the relevant slot in pmu_hw_events::events[] before clearing the bit in pmu_hw_events::used_mask such that the counter can be reallocated. Thus when armpmu_add() allocates a counter index from pmu_hw_events::used_mask, it should not be possible to observe a stale even in pmu_hw_events::events[] unless either pmu_hw_events::used_mask or pmu_hw_events::events[] have been corrupted. If this were to happen, we'd end up with two events with the same event->hw.idx, which would clash with each other during reprogramming, deletion, etc, and produce bogus results. Add a WARN_ON_ONCE() for this case so that we can detect if this ever occurs in practice. That possiblity aside, there's no need to call arm_pmu::disable(event) for the new event. The PMU reset code initialises the counter in a disabled state, and armpmu_del() will disable the counter before it can be reused. Remove the redundant disable. Signed-off-by: Mark Rutland Signed-off-by: Rob Herring (Arm) Reviewed-by: Anshuman Khandual Tested-by: James Clark Link: https://lore.kernel.org/r/20250218-arm-brbe-v19-v20-2-4e9922fc2e8e@kernel.org Signed-off-by: Will Deacon Signed-off-by: Sasha Levin --- drivers/perf/arm_pmu.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c index 398cce3d76fc4..2f33e69a8caf2 100644 --- a/drivers/perf/arm_pmu.c +++ b/drivers/perf/arm_pmu.c @@ -342,12 +342,10 @@ armpmu_add(struct perf_event *event, int flags) if (idx < 0) return idx; - /* - * If there is an event in the counter we are going to use then make - * sure it is disabled. - */ + /* The newly-allocated counter should be empty */ + WARN_ON_ONCE(hw_events->events[idx]); + event->hw.idx = idx; - armpmu->disable(event); hw_events->events[idx] = event; hwc->state = PERF_HES_STOPPED | PERF_HES_UPTODATE; -- 2.39.5