From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELsCW17Oq5zdgtAKudDc75TcAjfKRMviB+aeNRaqDwcZg9zbzPO+77nIlMR4/VbOHEAAccUq ARC-Seal: i=1; a=rsa-sha256; t=1521483936; cv=none; d=google.com; s=arc-20160816; b=hBdN+zlB7YUdmTowo1jfu1r4ucP/mXH2Jge5JB+j+Eu7j3CoU5+1EG+OXYrFCBVbAf kCFAJuzWFt8GmS8AYBJ0Q/PWf5C5RR63PN2pqU+qC+iuOQXsCSSFhTSJ2iaFxrG5bpzt Oq/8bhlVGLqqO2udyeDgSAQRKhgiVRBcgnE3yBByPJo53k5ilhLP4xZTvCAWqrHu3KHn 0QXEt6e2filmWCnD5K5dE9n/fh1Og1wotWUv7t1q2Yva884MqZjYGrB2SFIZzZ646OmM 9nMAfUMAKJuRRWmH5lcDwHMSMJmp5Q14DEzmCnvwC602TjXHn/o0IOIpuaRe3yxMjuV9 bDYg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=KanUTORzTvImLxCM+axveSXsTfREu8aGbmhpZPD74zg=; b=vw4YbdfGNhlECf+Sg6v163k1u9sWbmW6O6Sg7scKkbdwy8jw04JKkoHaAJzzNEpJCw /VcsidCGY35vjrrzcGS5LJb4snS7Fo8+t52LFPPPGQQvzVq7hwZcUw6EEhrXJ2RorLxk iGxDIcmfWsiGohMQjlMQ6QONJKiLt8QAvG1nZLGWDFD6lpAGqxvdL08fLoXlM40ZU20e gaOLPJliXqVgPwYRqtOJZFPhUqoOVy5yVNWFnofZ+9g/36Ud+ZRep27XRv2vhM3JfKxp hQWXy6UyoQlMt1VXSB//RMrzdhtwfguT+APIPmBVkc98kGk55JX/iguKc2zrUjYB6t9l E4GQ== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Paul E. McKenney" , Ingo Molnar , Peter Zijlstra , Sasha Levin Subject: [PATCH 4.9 170/241] sched: Stop switched_to_rt() from sending IPIs to offline CPUs Date: Mon, 19 Mar 2018 19:07:15 +0100 Message-Id: <20180319180758.198717661@linuxfoundation.org> X-Mailer: git-send-email 2.16.2 In-Reply-To: <20180319180751.172155436@linuxfoundation.org> References: <20180319180751.172155436@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1595390899532847799?= X-GMAIL-MSGID: =?utf-8?q?1595391539993404002?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: "Paul E. McKenney" [ Upstream commit 2fe2582649aa2355f79acddb86bd4d6c5363eb63 ] The rcutorture test suite occasionally provokes a splat due to invoking rt_mutex_lock() which needs to boost the priority of a task currently sitting on a runqueue that belongs to an offline CPU: WARNING: CPU: 0 PID: 12 at /home/paulmck/public_git/linux-rcu/arch/x86/kernel/smp.c:128 native_smp_send_reschedule+0x37/0x40 Modules linked in: CPU: 0 PID: 12 Comm: rcub/7 Not tainted 4.14.0-rc4+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 task: ffff9ed3de5f8cc0 task.stack: ffffbbf80012c000 RIP: 0010:native_smp_send_reschedule+0x37/0x40 RSP: 0018:ffffbbf80012fd10 EFLAGS: 00010082 RAX: 000000000000002f RBX: ffff9ed3dd9cb300 RCX: 0000000000000004 RDX: 0000000080000004 RSI: 0000000000000086 RDI: 00000000ffffffff RBP: ffffbbf80012fd10 R08: 000000000009da7a R09: 0000000000007b9d R10: 0000000000000001 R11: ffffffffbb57c2cd R12: 000000000000000d R13: ffff9ed3de5f8cc0 R14: 0000000000000061 R15: ffff9ed3ded59200 FS: 0000000000000000(0000) GS:ffff9ed3dea00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000080686f0 CR3: 000000001b9e0000 CR4: 00000000000006f0 Call Trace: resched_curr+0x61/0xd0 switched_to_rt+0x8f/0xa0 rt_mutex_setprio+0x25c/0x410 task_blocks_on_rt_mutex+0x1b3/0x1f0 rt_mutex_slowlock+0xa9/0x1e0 rt_mutex_lock+0x29/0x30 rcu_boost_kthread+0x127/0x3c0 kthread+0x104/0x140 ? rcu_report_unblock_qs_rnp+0x90/0x90 ? kthread_create_on_node+0x40/0x40 ret_from_fork+0x22/0x30 Code: f0 00 0f 92 c0 84 c0 74 14 48 8b 05 34 74 c5 00 be fd 00 00 00 ff 90 a0 00 00 00 5d c3 89 fe 48 c7 c7 a0 c6 fc b9 e8 d5 b5 06 00 <0f> ff 5d c3 0f 1f 44 00 00 8b 05 a2 d1 13 02 85 c0 75 38 55 48 But the target task's priority has already been adjusted, so the only purpose of switched_to_rt() invoking resched_curr() is to wake up the CPU running some task that needs to be preempted by the boosted task. But the CPU is offline, which presumably means that the task must be migrated to some other CPU, and that this other CPU will undertake any needed preemption at the time of migration. Because the runqueue lock is held when resched_curr() is invoked, we know that the boosted task cannot go anywhere, so it is not necessary to invoke resched_curr() in this particular case. This commit therefore makes switched_to_rt() refrain from invoking resched_curr() when the target CPU is offline. Signed-off-by: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- kernel/sched/rt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2206,7 +2206,7 @@ static void switched_to_rt(struct rq *rq if (tsk_nr_cpus_allowed(p) > 1 && rq->rt.overloaded) queue_push_tasks(rq); #endif /* CONFIG_SMP */ - if (p->prio < rq->curr->prio) + if (p->prio < rq->curr->prio && cpu_online(cpu_of(rq))) resched_curr(rq); } }