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 X-Spam-Level: X-Spam-Status: No, score=-12.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 066A4C282C4 for ; Mon, 4 Feb 2019 08:52:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C7A89217D6 for ; Mon, 4 Feb 2019 08:52:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728491AbfBDIwL (ORCPT ); Mon, 4 Feb 2019 03:52:11 -0500 Received: from terminus.zytor.com ([198.137.202.136]:42567 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726587AbfBDIwL (ORCPT ); Mon, 4 Feb 2019 03:52:11 -0500 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id x148poBs357484 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Mon, 4 Feb 2019 00:51:51 -0800 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id x148pokV357481; Mon, 4 Feb 2019 00:51:50 -0800 Date: Mon, 4 Feb 2019 00:51:50 -0800 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Elena Reshetova Message-ID: Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, acme@redhat.com, hpa@zytor.com, jolsa@redhat.com, keescook@chromium.org, peterz@infradead.org, torvalds@linux-foundation.org, alexander.shishkin@linux.intel.com, mingo@kernel.org, ishkamiel@gmail.com, elena.reshetova@intel.com, dwindsor@gmail.com Reply-To: peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, alexander.shishkin@linux.intel.com, acme@redhat.com, mingo@kernel.org, hpa@zytor.com, ishkamiel@gmail.com, elena.reshetova@intel.com, jolsa@redhat.com, keescook@chromium.org, dwindsor@gmail.com In-Reply-To: <1548678448-24458-2-git-send-email-elena.reshetova@intel.com> References: <1548678448-24458-2-git-send-email-elena.reshetova@intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/core] perf: Convert perf_event_context.refcount to refcount_t Git-Commit-ID: 8c94abbbe1ba24961278055434504b7dc3595415 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 8c94abbbe1ba24961278055434504b7dc3595415 Gitweb: https://git.kernel.org/tip/8c94abbbe1ba24961278055434504b7dc3595415 Author: Elena Reshetova AuthorDate: Mon, 28 Jan 2019 14:27:26 +0200 Committer: Ingo Molnar CommitDate: Mon, 4 Feb 2019 08:46:15 +0100 perf: Convert perf_event_context.refcount to refcount_t atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable perf_event_context.refcount is used as pure reference counter. Convert it to refcount_t and fix up the operations. ** Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. Please check Documentation/core-api/refcount-vs-atomic.rst for more information. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the perf_event_context.refcount it might make a difference in following places: - get_ctx(), perf_event_ctx_lock_nested(), perf_lock_task_context() and __perf_event_ctx_lock_double(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - put_ctx(): decrement in refcount_dec_and_test() provides RELEASE ordering and ACQUIRE ordering + control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook Signed-off-by: Elena Reshetova Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: acme@kernel.org Cc: namhyung@kernel.org Link: https://lkml.kernel.org/r/1548678448-24458-2-git-send-email-elena.reshetova@intel.com Signed-off-by: Ingo Molnar --- include/linux/perf_event.h | 3 ++- kernel/events/core.c | 12 ++++++------ 2 files changed, 8 insertions(+), 7 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index a79e59fc3b7d..6cb5d483ab34 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -54,6 +54,7 @@ struct perf_guest_info_callbacks { #include #include #include +#include #include struct perf_callchain_entry { @@ -737,7 +738,7 @@ struct perf_event_context { int nr_stat; int nr_freq; int rotate_disable; - atomic_t refcount; + refcount_t refcount; struct task_struct *task; /* diff --git a/kernel/events/core.c b/kernel/events/core.c index 5b89de7918d0..677164d54547 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1172,7 +1172,7 @@ static void perf_event_ctx_deactivate(struct perf_event_context *ctx) static void get_ctx(struct perf_event_context *ctx) { - WARN_ON(!atomic_inc_not_zero(&ctx->refcount)); + refcount_inc(&ctx->refcount); } static void free_ctx(struct rcu_head *head) @@ -1186,7 +1186,7 @@ static void free_ctx(struct rcu_head *head) static void put_ctx(struct perf_event_context *ctx) { - if (atomic_dec_and_test(&ctx->refcount)) { + if (refcount_dec_and_test(&ctx->refcount)) { if (ctx->parent_ctx) put_ctx(ctx->parent_ctx); if (ctx->task && ctx->task != TASK_TOMBSTONE) @@ -1268,7 +1268,7 @@ perf_event_ctx_lock_nested(struct perf_event *event, int nesting) again: rcu_read_lock(); ctx = READ_ONCE(event->ctx); - if (!atomic_inc_not_zero(&ctx->refcount)) { + if (!refcount_inc_not_zero(&ctx->refcount)) { rcu_read_unlock(); goto again; } @@ -1401,7 +1401,7 @@ retry: } if (ctx->task == TASK_TOMBSTONE || - !atomic_inc_not_zero(&ctx->refcount)) { + !refcount_inc_not_zero(&ctx->refcount)) { raw_spin_unlock(&ctx->lock); ctx = NULL; } else { @@ -4057,7 +4057,7 @@ static void __perf_event_init_context(struct perf_event_context *ctx) INIT_LIST_HEAD(&ctx->event_list); INIT_LIST_HEAD(&ctx->pinned_active); INIT_LIST_HEAD(&ctx->flexible_active); - atomic_set(&ctx->refcount, 1); + refcount_set(&ctx->refcount, 1); } static struct perf_event_context * @@ -10613,7 +10613,7 @@ __perf_event_ctx_lock_double(struct perf_event *group_leader, again: rcu_read_lock(); gctx = READ_ONCE(group_leader->ctx); - if (!atomic_inc_not_zero(&gctx->refcount)) { + if (!refcount_inc_not_zero(&gctx->refcount)) { rcu_read_unlock(); goto again; }