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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 74FF0C433EF for ; Wed, 22 Sep 2021 11:16:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4A54260F23 for ; Wed, 22 Sep 2021 11:16:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235603AbhIVLR6 (ORCPT ); Wed, 22 Sep 2021 07:17:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39256 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235552AbhIVLRo (ORCPT ); Wed, 22 Sep 2021 07:17:44 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EDF21C0617A7; Wed, 22 Sep 2021 04:14:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=1d0LvJ7ebosJy+t+gBdEEoeagZoG9oczZaU8O5nKVWA=; b=g9F/dbBs7Ryr8dOKRAH6XjNXvG 1W9jriIN8yNdeyqK1IgrbxFCNY1hmzbb5uTgmWp8Vh0behpmqZxPK/nH+Lx4msacql4izC5PQ5rsg ReZsBdN2feFoxfN19ZOLWwllqKx4QXhqVMXJyuEsneeLe4tpAe4EVU/0BMfj7sgcGn1YQHwiFw08K 0YsI8L3mnfxZzSTKQF782+45zwr9JSy8W1zOoBljqLjbWYfcnkZFCUZkSkiMKJgWyHPw/9gbU3q3G 48QekyYcfZSevx1hIoBVvytjgadb+BONmTylVdtEo8pcRNh9TRQZemK83uXz4bKTkLk68g9D8qaqM lhMGkbOQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mT09o-004irJ-0Y; Wed, 22 Sep 2021 11:11:28 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id B12AE300399; Wed, 22 Sep 2021 13:11:18 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 7B5882027194A; Wed, 22 Sep 2021 13:11:18 +0200 (CEST) Message-ID: <20210922110835.945716442@infradead.org> User-Agent: quilt/0.66 Date: Wed, 22 Sep 2021 13:05:07 +0200 From: Peter Zijlstra To: gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org, mbenes@suse.cz, pmladek@suse.com, mingo@kernel.org Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, joe.lawrence@redhat.com, fweisbec@gmail.com, tglx@linutronix.de, hca@linux.ibm.com, svens@linux.ibm.com, sumanthk@linux.ibm.com, live-patching@vger.kernel.org, paulmck@kernel.org Subject: [RFC][PATCH 1/7] sched,rcu: Rework try_invoke_on_locked_down_task() References: <20210922110506.703075504@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org Give try_invoke_on_locked_down_task() a saner name and have it return an int so that the caller might distinguish between different reasons of failure. Signed-off-by: Peter Zijlstra (Intel) --- include/linux/wait.h | 3 ++- kernel/rcu/tasks.h | 12 ++++++------ kernel/rcu/tree_stall.h | 8 ++++---- kernel/sched/core.c | 11 +++++------ 4 files changed, 17 insertions(+), 17 deletions(-) --- a/include/linux/wait.h +++ b/include/linux/wait.h @@ -1160,6 +1160,7 @@ int autoremove_wake_function(struct wait (wait)->flags = 0; \ } while (0) -bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg); +typedef int (*task_try_f)(struct task_struct *p, void *arg); +extern int task_try_func(struct task_struct *p, task_try_f func, void *arg); #endif /* _LINUX_WAIT_H */ --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -928,7 +928,7 @@ static void trc_read_check_handler(void } /* Callback function for scheduler to check locked-down task. */ -static bool trc_inspect_reader(struct task_struct *t, void *arg) +static int trc_inspect_reader(struct task_struct *t, void *arg) { int cpu = task_cpu(t); bool in_qs = false; @@ -939,7 +939,7 @@ static bool trc_inspect_reader(struct ta // If no chance of heavyweight readers, do it the hard way. if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) - return false; + return -EINVAL; // If heavyweight readers are enabled on the remote task, // we can inspect its state despite its currently running. @@ -947,7 +947,7 @@ static bool trc_inspect_reader(struct ta n_heavy_reader_attempts++; if (!ofl && // Check for "running" idle tasks on offline CPUs. !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) - return false; // No quiescent state, do it the hard way. + return -EINVAL; // No quiescent state, do it the hard way. n_heavy_reader_updates++; if (ofl) n_heavy_reader_ofl_updates++; @@ -962,7 +962,7 @@ static bool trc_inspect_reader(struct ta t->trc_reader_checked = true; if (in_qs) - return true; // Already in quiescent state, done!!! + return 0; // Already in quiescent state, done!!! // The task is in a read-side critical section, so set up its // state so that it will awaken the grace-period kthread upon exit @@ -970,7 +970,7 @@ static bool trc_inspect_reader(struct ta atomic_inc(&trc_n_readers_need_end); // One more to wait on. WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)); WRITE_ONCE(t->trc_reader_special.b.need_qs, true); - return true; + return 0; } /* Attempt to extract the state for the specified task. */ @@ -992,7 +992,7 @@ static void trc_wait_for_one_reader(stru // Attempt to nail down the task for inspection. get_task_struct(t); - if (try_invoke_on_locked_down_task(t, trc_inspect_reader, NULL)) { + if (!task_try_func(t, trc_inspect_reader, NULL)) { put_task_struct(t); return; } --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -240,16 +240,16 @@ struct rcu_stall_chk_rdr { * Report out the state of a not-running task that is stalling the * current RCU grace period. */ -static bool check_slow_task(struct task_struct *t, void *arg) +static int check_slow_task(struct task_struct *t, void *arg) { struct rcu_stall_chk_rdr *rscrp = arg; if (task_curr(t)) - return false; // It is running, so decline to inspect it. + return -EBUSY; // It is running, so decline to inspect it. rscrp->nesting = t->rcu_read_lock_nesting; rscrp->rs = t->rcu_read_unlock_special; rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry); - return true; + return 0; } /* @@ -283,7 +283,7 @@ static int rcu_print_task_stall(struct r raw_spin_unlock_irqrestore_rcu_node(rnp, flags); while (i) { t = ts[--i]; - if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr)) + if (task_try_func(t, check_slow_task, &rscr)) pr_cont(" P%d", t->pid); else pr_cont(" P%d/%d:%c%c%c%c", --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4106,7 +4106,7 @@ try_to_wake_up(struct task_struct *p, un } /** - * try_invoke_on_locked_down_task - Invoke a function on task in fixed state + * task_try_func - Invoke a function on task in fixed state * @p: Process for which the function is to be invoked, can be @current. * @func: Function to invoke. * @arg: Argument to function. @@ -4119,14 +4119,13 @@ try_to_wake_up(struct task_struct *p, un * lightweight. * * Returns: - * @false if the task slipped out from under the locks. - * @true if the task was locked onto a runqueue or is sleeping. - * However, @func can override this by returning @false. + * -EAGAIN: we raced against task movement/state + * *: as returned by @func */ -bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg) +int task_try_func(struct task_struct *p, task_try_f func, void *arg) { struct rq_flags rf; - bool ret = false; + int ret = -EAGAIN; /* raced, try again later */ struct rq *rq; raw_spin_lock_irqsave(&p->pi_lock, rf.flags);