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McKenney" To: linux-kernel@vger.kernel.org Cc: 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 2/4] srcu: Prevent __call_srcu() counter wrap with read-side critical section Date: Sun, 11 Nov 2018 12:08:55 -0800 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20181111200834.GA10983@linux.ibm.com> References: <20181111200834.GA10983@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18111120-0060-0000-0000-000002D0FDC2 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010028; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000270; SDB=6.01116027; UDB=6.00578737; IPR=6.00896127; MB=3.00024114; MTD=3.00000008; XFM=3.00000015; UTC=2018-11-11 20:09:02 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18111120-0061-0000-0000-0000472A0F8B Message-Id: <20181111200857.11711-2-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-11-11_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 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=8.0.1-1807170000 definitions=main-1811110192 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Ever since cdf7abc4610a ("srcu: Allow use of Tiny/Tree SRCU from both process and interrupt context"), it has been permissible to use SRCU read-side critical sections in interrupt context. This allows __call_srcu() to use SRCU read-side critical sections to prevent a new SRCU grace period from ending before the call to either srcu_funnel_gp_start() or srcu_funnel_exp_start completes, thus preventing SRCU grace-period counter overflow during that time. Note that this does not permit removal of the counter-wrap checks in srcu_gp_end(). These check are necessary to handle the case where a given CPU does not interact at all with SRCU for an extended time period. This commit therefore adds an SRCU read-side critical section to __call_srcu() in order to prevent grace period counter wrap during the funnel-locking process. Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index a8846ed7f352..60f3236beaf7 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -858,6 +858,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, rcu_callback_t func, bool do_norm) { unsigned long flags; + int idx; bool needexp = false; bool needgp = false; unsigned long s; @@ -871,6 +872,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, return; } rhp->func = func; + idx = srcu_read_lock(sp); local_irq_save(flags); sdp = this_cpu_ptr(sp->sda); spin_lock_rcu_node(sdp); @@ -892,6 +894,7 @@ void __call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, srcu_funnel_gp_start(sp, sdp, s, do_norm); else if (needexp) srcu_funnel_exp_start(sp, sdp->mynode, s); + srcu_read_unlock(sp, idx); } /** -- 2.17.1