From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 795C282864; Wed, 4 Jun 2025 10:01:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749031268; cv=none; b=SorhRLUi7AEbh5nAD5/2H0HG8knclqIfhfUpgZfeRSZ3TQh0cvqZB1Tx8Z5jOS1aaKXQpTCL/4WqFVPQ96bpO+Qf9D5Hd1ui8AW1zzVQWZx3GW7fA6P6JkZtoq/xhODUiHztuuW4LRUa7MO5hue+vj0mTjHHfE3Nrajcy9wCj94= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749031268; c=relaxed/simple; bh=g7dNmCFIuya1AhW9VqQ7BiqRh+rsuId820P66lxPe3I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WjfuZnhYpO4Wl/devvLufNYljiBOCsJwOCN1dCtK4UBi7tSKDwU7RmWE+LLkT2uVaWV94a7SLFAdaiRl6m1KVowYh5LUlOciCftPUV/ShOPCeHEUFyZTAUJP/RVLrZX5/Kqr6GnK+2YReD7vAsncbuwYuoiH7FtCvwF/MFr5wME= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=V5gVPwYN; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="V5gVPwYN" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=hvswKOspXfPTomvHlFFhmYJf0rg8SY9R3ztOupfQW1k=; b=V5gVPwYNk3egL6TbXhE4FB0B0O 9OWoVUpjbd6KhfBwhZs4MpN6QBPVxKc9M84ZPChKCN5d771V/VcxwIK5SrPd54p7HruLbXmcLa3OQ cwhxmojiIlLzewnu7hRud3tIaZgHh6g15hk6XDCXKRaSyXx6AEvceQ0Bb0JH8+2rLPsKKaPxJnWwR a+VO8SbpyJoBRODZ6x3ABpL/WJsHlOCYvuYSRaR+Rz/XdIc8o80Y8tmJwA6WEr6XR1JpE2R7PrvJv OwDfWlH4zt+sR1HTcLNOg+UFP24YEW0rDQ6mACnzbKUXMeOWGZdZdE2JTbtlj/oXqyJYuLJgv3ug0 msCswAtw==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uMkvV-00000000t0z-2SCQ; Wed, 04 Jun 2025 10:00:53 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id CC1C830078B; Wed, 4 Jun 2025 12:00:52 +0200 (CEST) Date: Wed, 4 Jun 2025 12:00:52 +0200 From: Peter Zijlstra To: Luo Gengkun Cc: mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, davidcc@google.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/2] perf/core: Fix WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0) in perf_cgroup_switch Message-ID: <20250604100052.GH38114@noisy.programming.kicks-ass.net> References: <20250604033924.3914647-1-luogengkun@huaweicloud.com> <20250604033924.3914647-3-luogengkun@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250604033924.3914647-3-luogengkun@huaweicloud.com> On Wed, Jun 04, 2025 at 03:39:24AM +0000, Luo Gengkun wrote: > There may be concurrency between perf_cgroup_switch and > perf_cgroup_event_disable. Consider the following scenario: after a new > perf cgroup event is created on CPU0, the new event may not trigger > a reprogramming, causing ctx->is_active to be 0. In this case, when CPU1 > disables this perf event, it executes __perf_remove_from_context-> > list _del_event->perf_cgroup_event_disable on CPU1, which causes a race > with perf_cgroup_switch running on CPU0. > > The following describes the details of this concurrency scenario: > > CPU0 CPU1 > > perf_cgroup_switch: > ... > # cpuctx->cgrp is not NULL here > if (READ_ONCE(cpuctx->cgrp) == NULL) > return; > > perf_remove_from_context: > ... > raw_spin_lock_irq(&ctx->lock); > ... > # ctx->is_active == 0 because reprogramm is not > # tigger, so CPU1 can do __perf_remove_from_context > # for CPU0 > __perf_remove_from_context: > perf_cgroup_event_disable: > ... > if (--ctx->nr_cgroups) > ... > > # this warning will happened because CPU1 changed > # ctx.nr_cgroups to 0. > WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0); > > To fix this problem, expand the lock-holding critical section in > perf_cgroup_switch. > > Fixes: db4a835601b7 ("perf/core: Set cgroup in CPU contexts for new cgroup events") > Signed-off-by: Luo Gengkun > --- Right, so how about we simply re-check the condition once we take the lock? Also, take the opportunity to convert to guard instead of adding goto unlock. --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -207,6 +207,19 @@ static void perf_ctx_unlock(struct perf_ __perf_ctx_unlock(&cpuctx->ctx); } +typedef struct { + struct perf_cpu_context *cpuctx; + struct perf_event_context *ctx; +} class_perf_ctx_lock_t; + +static inline void class_perf_ctx_lock_destructor(class_perf_ctx_lock_t *_T) +{ perf_ctx_unlock(_T->cpuctx, _T->ctx); } + +static inline class_perf_ctx_lock_t +class_perf_ctx_lock_constructor(struct perf_cpu_context *cpuctx, + struct perf_event_context *ctx) +{ perf_ctx_lock(cpuctx, ctx); return (class_perf_ctx_lock_t){ cpuctx, ctx }; } + #define TASK_TOMBSTONE ((void *)-1L) static bool is_kernel_event(struct perf_event *event) @@ -944,7 +957,13 @@ static void perf_cgroup_switch(struct ta if (READ_ONCE(cpuctx->cgrp) == cgrp) return; - perf_ctx_lock(cpuctx, cpuctx->task_ctx); + guard(perf_ctx_lock)(cpuctx, cpuctx->task_ctx); + /* + * Re-check, could've raced vs perf_remove_from_context(). + */ + if (READ_ONCE(cpuctx->cgrp) == NULL) + return; + perf_ctx_disable(&cpuctx->ctx, true); ctx_sched_out(&cpuctx->ctx, NULL, EVENT_ALL|EVENT_CGROUP); @@ -962,7 +981,6 @@ static void perf_cgroup_switch(struct ta ctx_sched_in(&cpuctx->ctx, NULL, EVENT_ALL|EVENT_CGROUP); perf_ctx_enable(&cpuctx->ctx, true); - perf_ctx_unlock(cpuctx, cpuctx->task_ctx); } static int perf_cgroup_ensure_storage(struct perf_event *event,