From nobody Wed Nov 27 04:33:46 2024 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 068CC1E526; Sat, 12 Oct 2024 14:16:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728742569; cv=none; b=dfOaZEWkf+/rhamcifhPp7Gyu4/BoaHpcVBgZg2QQ64hiI2nl7GzkEBvQRMGg058s7uVWakFSm5NMuHbXHRCnQl3FvGZgL1gOaQbgTpu5xqMrxozYzmTXPljxBNhrWrPQcNOtOcTFFKIPkch/QzB9S6HYxSLnXlunjWgXjwEaS4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728742569; c=relaxed/simple; bh=q4lzSb4mhyElHXqrkJUtsN1mesy0JXYPWsfWQs++QBc=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=NssQ6E56Z7QUAdSrcNUE507TAWDPzhjo1IUBMkkBvvOEi5lIi7W068qZ9sQRBOoBzn8XuVXITUJq9ifA+PALznA+U71sS60DmehR16u9B0higizCX/mC/vjoEypDHhHvufgz1w0wkpZGGnVusJVgxFOf55rqVSJINxCUgJOwAuw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=kzj5zkXH; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=2zwbb5l5; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="kzj5zkXH"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="2zwbb5l5" Date: Sat, 12 Oct 2024 14:15:58 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1728742559; 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: in-reply-to:in-reply-to:references:references; bh=DSJUsJmMXuNxAW3lPFWmBxeMILn5o2oWAWv+n5b7Cc4=; b=kzj5zkXHkN2HPUz3uiSRzulK2gc77hMWwigBp5f6BZUotkUSJU3mxfXblwBxRTknhWTxig OB50iS93GYEpYN5rS3vymMa1rPx9QsjCJ+HF3Rr4ccw5jEipM0xh+PtMoBwdcPM6qikTGs i1jt6CGCXzlLJWmXyain6S/EQ7MCPZ+3srHiPiGVnsQb/PMvx+B89ZC1vlEzPGRG2afARF 9rRdREVxessgBiavuG3Km9T5ZYWID+ttePmgjkVCQ6H2qGWcR3Yhu+9k0nBwXhNKmyti2a xakPzRZFlq/JxWUAuyVC/b8NjDOXPKALwcucnD7KHKE6d4MovA5dnZSCLd696A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1728742559; 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: in-reply-to:in-reply-to:references:references; bh=DSJUsJmMXuNxAW3lPFWmBxeMILn5o2oWAWv+n5b7Cc4=; b=2zwbb5l5PNfAWGstPWj63rc5fjl3FwERjjQcMrdKs0E7bXhGAcq83mT9OpWdWwtnF9fKxT Wk22Kho8mieWlgDQ== 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: sched/urgent] sched: Fix external p->on_rq users Cc: Sean Christopherson , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20241010091843.GK33184@noisy.programming.kicks-ass.net> References: <20241010091843.GK33184@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <172874255804.1442.16221172414886128944.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the sched/urgent branch of tip: Commit-ID: 1cc2f68c016ad3ac8b3a0495797dd61e19a10025 Gitweb: https://git.kernel.org/tip/1cc2f68c016ad3ac8b3a0495797dd61e1= 9a10025 Author: Peter Zijlstra AuthorDate: Thu, 10 Oct 2024 11:38:10 +02:00 Committer: Peter Zijlstra CommitterDate: Fri, 11 Oct 2024 10:49:33 +02:00 sched: Fix external p->on_rq users Sean noted that ever since commit 152e11f6df29 ("sched/fair: Implement delayed dequeue") KVM's preemption notifiers have started mis-classifying preemption vs blocking. Notably p->on_rq is no longer sufficient to determine if a task is runnable or blocked -- the aforementioned commit introduces tasks that remain on the runqueue even through they will not run again, and should be considered blocked for many cases. Add the task_is_runnable() helper to classify things and audit all external users of the p->on_rq state. Also add a few comments. Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue") Reported-by: Sean Christopherson Tested-by: Sean Christopherson Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20241010091843.GK33184@noisy.programming.ki= cks-ass.net --- include/linux/sched.h | 5 +++++ kernel/events/core.c | 2 +- kernel/freezer.c | 7 ++++++- kernel/rcu/tasks.h | 9 +++++++++ kernel/sched/core.c | 12 +++++++++--- kernel/time/tick-sched.c | 5 +++++ kernel/trace/trace_selftest.c | 2 +- virt/kvm/kvm_main.c | 2 +- 8 files changed, 37 insertions(+), 7 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index e6ee425..8a9517e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2133,6 +2133,11 @@ static inline void set_task_cpu(struct task_struct *= p, unsigned int cpu) =20 #endif /* CONFIG_SMP */ =20 +static inline bool task_is_runnable(struct task_struct *p) +{ + return p->on_rq && !p->se.sched_delayed; +} + extern bool sched_task_on_rq(struct task_struct *p); extern unsigned long get_wchan(struct task_struct *p); extern struct task_struct *cpu_curr_snapshot(int cpu); diff --git a/kernel/events/core.c b/kernel/events/core.c index e3589c4..cdd0976 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9251,7 +9251,7 @@ static void perf_event_switch(struct task_struct *tas= k, }, }; =20 - if (!sched_in && task->on_rq) { + if (!sched_in && task_is_runnable(task)) { switch_event.event_id.header.misc |=3D PERF_RECORD_MISC_SWITCH_OUT_PREEMPT; } diff --git a/kernel/freezer.c b/kernel/freezer.c index 44bbd7d..8d530d0 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -109,7 +109,12 @@ static int __set_task_frozen(struct task_struct *p, vo= id *arg) { unsigned int state =3D READ_ONCE(p->__state); =20 - if (p->on_rq) + /* + * Allow freezing the sched_delayed tasks; they will not execute until + * ttwu() fixes them up, so it is safe to swap their state now, instead + * of waiting for them to get fully dequeued. + */ + if (task_is_runnable(p)) return 0; =20 if (p !=3D current && task_curr(p)) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 6333f4c..4d7ee95 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -986,6 +986,15 @@ static bool rcu_tasks_is_holdout(struct task_struct *t) return false; =20 /* + * t->on_rq && !t->se.sched_delayed *could* be considered sleeping but + * since it is a spurious state (it will transition into the + * traditional blocked state or get woken up without outside + * dependencies), not considering it such should only affect timing. + * + * Be conservative for now and not include it. + */ + + /* * Idle tasks (or idle injection) within the idle loop are RCU-tasks * quiescent states. But CPU boot code performed by the idle task * isn't a quiescent state. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 71232f8..7db711b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -548,6 +548,11 @@ sched_core_dequeue(struct rq *rq, struct task_struct *= p, int flags) { } * ON_RQ_MIGRATING state is used for migration without holding both * rq->locks. It indicates task_cpu() is not stable, see task_rq_lock(). * + * Additionally it is possible to be ->on_rq but still be considered not + * runnable when p->se.sched_delayed is true. These tasks are on the run= queue + * but will be dequeued as soon as they get picked again. See the + * task_is_runnable() helper. + * * p->on_cpu <- { 0, 1 }: * * is set by prepare_task() and cleared by finish_task() such that it wi= ll be @@ -4317,9 +4322,10 @@ static bool __task_needs_rq_lock(struct task_struct = *p) * @arg: Argument to function. * * Fix the task in it's current state by avoiding wakeups and or rq operat= ions - * and call @func(@arg) on it. This function can use ->on_rq and task_cur= r() - * to work out what the state is, if required. Given that @func can be in= voked - * with a runqueue lock held, it had better be quite lightweight. + * and call @func(@arg) on it. This function can use task_is_runnable() a= nd + * task_curr() to work out what the state is, if required. Given that @fu= nc + * can be invoked with a runqueue lock held, it had better be quite + * lightweight. * * Returns: * Whatever @func returns diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 753a184..59efa14 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -435,6 +435,11 @@ static void tick_nohz_kick_task(struct task_struct *ts= k) * tick_nohz_task_switch() * LOAD p->tick_dep_mask */ + // XXX given a task picks up the dependency on schedule(), should we + // only care about tasks that are currently on the CPU instead of all + // that are on the runqueue? + // + // That is, does this want to be: task_on_cpu() / task_curr()? if (!sched_task_on_rq(tsk)) return; =20 diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c index c4ad7cd..1469dd8 100644 --- a/kernel/trace/trace_selftest.c +++ b/kernel/trace/trace_selftest.c @@ -1485,7 +1485,7 @@ trace_selftest_startup_wakeup(struct tracer *trace, s= truct trace_array *tr) /* reset the max latency */ tr->max_latency =3D 0; =20 - while (p->on_rq) { + while (task_is_runnable(p)) { /* * Sleep to make sure the -deadline thread is asleep too. * On virtual machines we can't rely on timings, diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 05cbb25..0c666f1 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -6387,7 +6387,7 @@ static void kvm_sched_out(struct preempt_notifier *pn, =20 WRITE_ONCE(vcpu->scheduled_out, true); =20 - if (current->on_rq && vcpu->wants_to_run) { + if (task_is_runnable(current) && vcpu->wants_to_run) { WRITE_ONCE(vcpu->preempted, true); WRITE_ONCE(vcpu->ready, true); }