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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 30 May 2019 16:17:13 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22035.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x4UFHC8930736452 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 30 May 2019 15:17:12 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 44A26B2075; Thu, 30 May 2019 15:17:12 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2F4DDB206E; Thu, 30 May 2019 15:17:12 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.216]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 30 May 2019 15:17:12 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id BC50916C5D9F; Thu, 30 May 2019 08:17:13 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 10/21] rcutorture: Give the scheduler a chance on PREEMPT && NO_HZ_FULL kernels Date: Thu, 30 May 2019 08:17:01 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190530151650.GA422@linux.ibm.com> References: <20190530151650.GA422@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19053015-0072-0000-0000-000004354F4A X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011185; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000286; SDB=6.01210791; UDB=6.00636161; IPR=6.00991825; MB=3.00027120; MTD=3.00000008; XFM=3.00000015; UTC=2019-05-30 15:17:17 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19053015-0073-0000-0000-00004C6B6B5C Message-Id: <20190530151712.1612-10-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-05-30_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=38 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905300108 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In !PREEMPT kernels, cond_resched() is a no-op. In NO_HZ_FULL kernels, in-kernel execution (such as that of rcutorture's kthreads) might extend indefinitely without the scheduler gaining the aid of a scheduling-clock interrupt. This combination can make the interaction of an rcutorture forward-progress test and a CPU-hotplug stop_machine operation make less forward progress than one might like. Additionally, Sebastian Siewior notes that NO_HZ_FULL kernels have a scheduler check upon return to userspace execution, which suggests that in-kernel emulation of tight userspace loops containing system calls doing call_rcu() might also need explicit checks in the PREEMPT && NO_HZ_FULL case. This commit therefore introduces a rcu_torture_fwd_prog_cond_resched() function that explicitly invokes schedule() in such kernels whenever need_resched() returns true, while retaining use of cond_resched() for kernels that are either !PREEMPT or !NO_HZ_FULL. Signed-off-by: Paul E. McKenney --- kernel/rcu/rcutorture.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 6a4558532eac..ef6f6dedf4c4 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -1667,6 +1667,17 @@ static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp) spin_unlock_irqrestore(&rcu_fwd_lock, flags); } +// Give the scheduler a chance, even on nohz_full CPUs. +static void rcu_torture_fwd_prog_cond_resched(void) +{ + if (IS_ENABLED(CONFIG_PREEMPT) && IS_ENABLED(CONFIG_NO_HZ_FULL)) { + if (need_resched()) + schedule(); + } else { + cond_resched(); + } +} + /* * Free all callbacks on the rcu_fwd_cb_head list, either because the * test is over or because we hit an OOM event. @@ -1690,7 +1701,7 @@ static unsigned long rcu_torture_fwd_prog_cbfree(void) spin_unlock_irqrestore(&rcu_fwd_lock, flags); kfree(rfcp); freed++; - cond_resched(); + rcu_torture_fwd_prog_cond_resched(); } return freed; } @@ -1734,7 +1745,7 @@ static void rcu_torture_fwd_prog_nr(int *tested, int *tested_tries) udelay(10); cur_ops->readunlock(idx); if (!fwd_progress_need_resched || need_resched()) - cond_resched(); + rcu_torture_fwd_prog_cond_resched(); } (*tested_tries)++; if (!time_before(jiffies, stopat) && @@ -1817,7 +1828,7 @@ static void rcu_torture_fwd_prog_cr(void) rfcp->rfc_gps = 0; } cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr); - cond_resched(); + rcu_torture_fwd_prog_cond_resched(); } stoppedat = jiffies; n_launders_cb_snap = READ_ONCE(n_launders_cb); -- 2.17.1