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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, Liu Song , Liu Song , "Paul E . McKenney" Subject: [PATCH tip/core/rcu 05/18] rcu: Set rcutree.kthread_prio sysfs access to read-only Date: Tue, 26 Mar 2019 16:13:01 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190326231253.GA18343@linux.ibm.com> References: <20190326231253.GA18343@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19032623-0052-0000-0000-000003A18729 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010820; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000282; SDB=6.01180133; UDB=6.00617572; IPR=6.00960848; MB=3.00026169; MTD=3.00000008; XFM=3.00000015; UTC=2019-03-26 23:13:20 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19032623-0053-0000-0000-00006048D814 Message-Id: <20190326231314.19518-5-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-03-26_15:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=29 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-1903260156 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Liu Song The rcutree.kthread_prio kernel-boot parameter is used to set the priority for boost (rcub), per-CPU (rcuc), and grace-period (rcu_preempt or rcu_sched) kthreads. It is also used by rcutorture to check whether it is possible to meaningfully test RCU priority boosting. However, all of these cases will either ignore or be confused by any post-boot changes to rcutree.kthread_prio. Note that the user really can change the priorities of all of these kthreads using chrt, given sufficient privileges. Therefore, the read-write nature of sysfs access to rcutree.kthread_prio is thus at best an attractive nuisance. This commit therefore changes sysfs access to rcutree.kthread_prio to be read-only. Signed-off-by: Liu Song Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 2f78a115d34c..296131450414 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -149,7 +149,7 @@ static void sync_sched_exp_online_cleanup(int cpu); /* rcuc/rcub kthread realtime priority */ static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0; -module_param(kthread_prio, int, 0644); +module_param(kthread_prio, int, 0444); /* Delay in jiffies for grace-period initialization delays, debug only. */ -- 2.17.1