From nobody Mon Feb 9 04:14:34 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2FB92223709 for ; Wed, 14 May 2025 08:44:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747212273; cv=none; b=qUmf1Ske6bSCRhupGqNOJ7e/lZodJM1A8MliJ+lz4A1HeL4QEJE7nXMqfqu/t64c97aPnp+fXKaX34YEdlNkz6XKtih5MjdfGBXuVLLU3kGV+UjV6Rv6uPWcHfMmSn2+nUdhf18cQEP/q6Ti+PXs1kutqwQLke0vjBEVG2DQSZA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747212273; c=relaxed/simple; bh=WCCivkh+F3BfBeMHvOTrvD+/zKrI0ugclHHfXIfbsAY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mCpNH3f0dzQOxaCMJsZZPPhNwAYz3Knt54ETr1riFkiZGkY1ip37UBSOfCBSXqQBwWY4qK2mWZz/gxbb3LFLvtkMaQD0nkz+OKygzqHifUlix9igkOu35ZBUaCk44W4AY3vjY+BDKYapD32LcKr57zswfl/wSrgqQeo5f1kDcCA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=VnzzTqQ/; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VnzzTqQ/" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1747212270; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EKRhk+lgSAKiOsPo3FIiWva9od5/EemvjnyRISItWAs=; b=VnzzTqQ/InsUx0cdiKot1XsaYBwHeCHhg53FAB6AGjwz6lGYzPWEckYCLPLZfRfqcqJBoq eDw40cnd3yE9CICNboEp8yr9pxoHzyr679xSDu+1VDMMHCYP7wyYHI4RqJtSqIgj241ymD vNiwX72M15StfvtM3TupHjUKtLmsA10= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-668-MlErnUgxOXys0FyakfiC-w-1; Wed, 14 May 2025 04:44:27 -0400 X-MC-Unique: MlErnUgxOXys0FyakfiC-w-1 X-Mimecast-MFC-AGG-ID: MlErnUgxOXys0FyakfiC-w_1747212265 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D4AC0180048E; Wed, 14 May 2025 08:44:25 +0000 (UTC) Received: from gmonaco-thinkpadt14gen3.rmtit.com (unknown [10.44.32.189]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 9D5AF1953B82; Wed, 14 May 2025 08:44:21 +0000 (UTC) From: Gabriele Monaco To: linux-kernel@vger.kernel.org, Steven Rostedt , linux-trace-kernel@vger.kernel.org Cc: Gabriele Monaco , Ingo Molnar , Peter Zijlstra , Nam Cao , Tomas Glozar , Juri Lelli Subject: [RFC PATCH v2 10/12] rv: Retry when da monitor detects race conditions Date: Wed, 14 May 2025 10:43:12 +0200 Message-ID: <20250514084314.57976-11-gmonaco@redhat.com> In-Reply-To: <20250514084314.57976-1-gmonaco@redhat.com> References: <20250514084314.57976-1-gmonaco@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Content-Type: text/plain; charset="utf-8" DA monitor can be accessed from multiple cores simultaneously, this is likely, for instance when dealing with per-task monitors reacting on events that do not always occur on the CPU where the task is running. This can cause race conditions where two events change the next state and we see inconsistent values. E.g.: [62] event_srs: 27: sleepable x sched_wakeup -> running (final) [63] event_srs: 27: sleepable x sched_set_state_sleepable -> sleepable [63] error_srs: 27: event sched_switch_suspend not expected in the state = running In this case the monitor fails because the event on CPU 62 wins against the one on CPU 63, although the correct state should have been sleepable, since the task get suspended. Detect if the current state was modified by using try_cmpxchg while storing the next value. If it was, try again reading the current state. After a maximum number of failed retries, react as if it was an error with invalid current state (we cannot determine it). Monitors where this type of condition can occur must be able to account for racing events in any possible order, as we cannot know the winner. Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Gabriele Monaco --- include/linux/rv.h | 3 ++- include/rv/da_monitor.h | 53 +++++++++++++++++++++++++++++++---------- 2 files changed, 42 insertions(+), 14 deletions(-) diff --git a/include/linux/rv.h b/include/linux/rv.h index 3452b5e4b29e..a83a81ac6e46 100644 --- a/include/linux/rv.h +++ b/include/linux/rv.h @@ -7,7 +7,8 @@ #ifndef _LINUX_RV_H #define _LINUX_RV_H =20 -#define MAX_DA_NAME_LEN 32 +#define MAX_DA_NAME_LEN 32 +#define MAX_DA_RETRY_RACING_EVENTS 3 =20 #ifdef CONFIG_RV /* diff --git a/include/rv/da_monitor.h b/include/rv/da_monitor.h index 215c3eb770cc..8b714e3085a5 100644 --- a/include/rv/da_monitor.h +++ b/include/rv/da_monitor.h @@ -82,16 +82,19 @@ static inline void da_monitor_reset_##name(struct da_mo= nitor *da_mon) \ */ \ static inline type da_monitor_curr_state_##name(struct da_monitor *da_mon)= \ { \ - return da_mon->curr_state; \ + return READ_ONCE(da_mon->curr_state); \ } \ \ /* \ * da_monitor_set_state_##name - set the new current state \ + * \ + * return false without the change in case the state was modified elsewher= e \ */ \ -static inline void \ -da_monitor_set_state_##name(struct da_monitor *da_mon, enum states_##name = state) \ +static inline bool \ +da_monitor_set_state_##name(struct da_monitor *da_mon, enum states_##name = prev_state, \ + enum states_##name state) \ { \ - da_mon->curr_state =3D state; \ + return try_cmpxchg(&da_mon->curr_state, &prev_state, state); \ } \ \ /* \ @@ -150,17 +153,29 @@ static inline bool da_monitor_handling_event_##name(s= truct da_monitor *da_mon) * Event handler for implicit monitors. Implicit monitor is the one which = the * handler does not need to specify which da_monitor to manipulate. Exampl= es * of implicit monitor are the per_cpu or the global ones. + * + * Retry, in case there is a race while getting and setting the next state + * return an invalid current state if we run out of retries. The monitor s= hould + * be able to handle various orders. */ #define DECLARE_DA_MON_MODEL_HANDLER_IMPLICIT(name, type) \ \ static inline bool \ da_event_##name(struct da_monitor *da_mon, enum events_##name event) \ { \ - type curr_state =3D da_monitor_curr_state_##name(da_mon); \ - type next_state =3D model_get_next_state_##name(curr_state, event); \ + bool changed; \ + type curr_state, next_state; \ \ - if (next_state !=3D INVALID_STATE) { \ - da_monitor_set_state_##name(da_mon, next_state); \ + for (int i =3D 0; i < MAX_DA_RETRY_RACING_EVENTS; i++) { \ + curr_state =3D da_monitor_curr_state_##name(da_mon); \ + next_state =3D model_get_next_state_##name(curr_state, event); \ + if (next_state =3D=3D INVALID_STATE) \ + break; \ + changed =3D da_monitor_set_state_##name(da_mon, curr_state, next_state);= \ + if (unlikely(!changed)) { \ + curr_state =3D -1; \ + continue; \ + } \ \ trace_event_##name(model_get_state_name_##name(curr_state), \ model_get_event_name_##name(event), \ @@ -181,17 +196,29 @@ da_event_##name(struct da_monitor *da_mon, enum event= s_##name event) \ =20 /* * Event handler for per_task monitors. + * + * Retry, in case there is a race while getting and setting the next state + * return an invalid current state if we run out of retries. The monitor s= hould + * be able to handle various orders. */ #define DECLARE_DA_MON_MODEL_HANDLER_PER_TASK(name, type) \ \ static inline bool da_event_##name(struct da_monitor *da_mon, struct task_= struct *tsk, \ enum events_##name event) \ { \ - type curr_state =3D da_monitor_curr_state_##name(da_mon); \ - type next_state =3D model_get_next_state_##name(curr_state, event); \ - \ - if (next_state !=3D INVALID_STATE) { \ - da_monitor_set_state_##name(da_mon, next_state); \ + bool changed; \ + type curr_state, next_state; \ + \ + for (int i =3D 0; i < MAX_DA_RETRY_RACING_EVENTS; i++) { \ + curr_state =3D da_monitor_curr_state_##name(da_mon); \ + next_state =3D model_get_next_state_##name(curr_state, event); \ + if (next_state =3D=3D INVALID_STATE) \ + break; \ + changed =3D da_monitor_set_state_##name(da_mon, curr_state, next_state);= \ + if (unlikely(!changed)) { \ + curr_state =3D -1; \ + continue; \ + } \ \ trace_event_##name(tsk->pid, \ model_get_state_name_##name(curr_state), \ --=20 2.49.0