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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EA16FC433FE for ; Wed, 5 Oct 2022 11:26:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229727AbiJEL0t (ORCPT ); Wed, 5 Oct 2022 07:26:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56174 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229605AbiJEL0r (ORCPT ); Wed, 5 Oct 2022 07:26:47 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F22D45B7AE; Wed, 5 Oct 2022 04:26:44 -0700 (PDT) Date: Wed, 05 Oct 2022 11:26:40 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1664969202; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=ej3UBlGQFDLBvEmuT13sjKtZ9lSjk7GO7M5troNJt9Y=; b=Nrnva0LfxW8uydoUizRaTU0/JjDe0c6gFBuybTbFjtWqIqujAhoTQdlA8Llp+SG62dJhNt jSNcENz+ty5NFbrn3R1t1hrCn89slkauiFmY4GmNszw55DKHy59/BG9EpRMhrKRQpL3jHF 7fUGJLgxoXF49EZ+/OpKKItvF1cUVErpMfK1DGR291Tm0kT0XjD/0nYO5v4h0FIBgXQ9e3 UVxcF7rre95Sg/hpSVTBv8Eo9GiUl0WOtidUp6EhSVlLFSzeuWzlN53KIU22hLrXB+c3nN k9M+e1tZx8NINCbcKGxDykL83w3P6c22PIhSSm8mcCVq8VCTOW3a/pT62dSNFQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1664969202; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=ej3UBlGQFDLBvEmuT13sjKtZ9lSjk7GO7M5troNJt9Y=; b=FEPe00S5sbTR+qoKwrMJ0UC2uO3CnQM9XxYv3KSwPrGv05XHWnQ/00ESzc4HIBa+KiCta4 rpjyHkaEeKfdRDDQ== From: "tip-bot2 for Peter Zijlstra" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: perf/core] perf/hw_breakpoint: Annotate tsk->perf_event_mutex vs ctx->mutex Cc: "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org MIME-Version: 1.0 Message-ID: <166496920036.401.9244922544094908473.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the perf/core branch of tip: Commit-ID: 82aad7ff7ac25c8cf09d491ae23b9823f1901486 Gitweb: https://git.kernel.org/tip/82aad7ff7ac25c8cf09d491ae23b9823f1901486 Author: Peter Zijlstra AuthorDate: Tue, 04 Oct 2022 12:20:39 +02:00 Committer: Peter Zijlstra CommitterDate: Tue, 04 Oct 2022 13:32:09 +02:00 perf/hw_breakpoint: Annotate tsk->perf_event_mutex vs ctx->mutex Perf fuzzer gifted a lockdep splat: perf_event_init_context() mutex_lock(parent_ctx->mutex); (B) inherit_task_group() inherit_group() inherit_event() perf_event_alloc() perf_try_init_event() := hw_breakpoint_event_init() register_perf_hw_breakpoint() mutex_lock(child->perf_event_mutex); (A) Which is against the normal (documented) order. Now, this is a false positive in that child is not published yet, but also inherited events never end up on ->perf_event_list. Annotate this one away. Fixes: 0912037fec11 ("perf/hw_breakpoint: Reduce contention with large number of tasks") Signed-off-by: Peter Zijlstra (Intel) --- kernel/events/hw_breakpoint.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c index 7ef0e98..c379770 100644 --- a/kernel/events/hw_breakpoint.c +++ b/kernel/events/hw_breakpoint.c @@ -117,7 +117,17 @@ static struct mutex *bp_constraints_lock(struct perf_event *bp) struct mutex *tsk_mtx = get_task_bps_mutex(bp); if (tsk_mtx) { - mutex_lock(tsk_mtx); + /* + * Fully analogous to the perf_try_init_event() nesting + * argument in the comment near perf_event_ctx_lock_nested(); + * this child->perf_event_mutex cannot ever deadlock against + * the parent->perf_event_mutex usage from + * perf_event_task_{en,dis}able(). + * + * Specifically, inherited events will never occur on + * ->perf_event_list. + */ + mutex_lock_nested(tsk_mtx, SINGLE_DEPTH_NESTING); percpu_down_read(&bp_cpuinfo_sem); } else { percpu_down_write(&bp_cpuinfo_sem);