From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755871AbaJ1WAS (ORCPT ); Tue, 28 Oct 2014 18:00:18 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:43315 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754614AbaJ1V5d (ORCPT ); Tue, 28 Oct 2014 17:57:33 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.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, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 10/10] cpu: Avoid puts_pending overflow Date: Tue, 28 Oct 2014 14:53:37 -0700 Message-Id: <1414533217-24910-10-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1414533217-24910-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20141028215140.GA23970@linux.vnet.ibm.com> <1414533217-24910-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14102821-0033-0000-0000-000000E3EBB7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" A long string of get_online_cpus() with each followed by a put_online_cpu() that fails to acquire cpu_hotplug.lock can result in overflow of the cpu_hotplug.puts_pending counter. Although this is perhaps improbably, a system with absolutely no CPU-hotplug operations will have an arbitrarily long time in which this overflow could occur. This commit therefore adds overflow checks to get_online_cpus() and try_get_online_cpus(). Signed-off-by: Paul E. McKenney --- kernel/cpu.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/kernel/cpu.c b/kernel/cpu.c index 90a3d017b90c..5d220234b3ca 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -86,6 +86,16 @@ static struct { #define cpuhp_lock_acquire() lock_map_acquire(&cpu_hotplug.dep_map) #define cpuhp_lock_release() lock_map_release(&cpu_hotplug.dep_map) +static void apply_puts_pending(int max) +{ + int delta; + + if (atomic_read(&cpu_hotplug.puts_pending) >= max) { + delta = atomic_xchg(&cpu_hotplug.puts_pending, 0); + cpu_hotplug.refcount -= delta; + } +} + void get_online_cpus(void) { might_sleep(); @@ -93,6 +103,7 @@ void get_online_cpus(void) return; cpuhp_lock_acquire_read(); mutex_lock(&cpu_hotplug.lock); + apply_puts_pending(65536); cpu_hotplug.refcount++; mutex_unlock(&cpu_hotplug.lock); } @@ -105,6 +116,7 @@ bool try_get_online_cpus(void) if (!mutex_trylock(&cpu_hotplug.lock)) return false; cpuhp_lock_acquire_tryread(); + apply_puts_pending(65536); cpu_hotplug.refcount++; mutex_unlock(&cpu_hotplug.lock); return true; @@ -161,12 +173,7 @@ void cpu_hotplug_begin(void) cpuhp_lock_acquire(); for (;;) { mutex_lock(&cpu_hotplug.lock); - if (atomic_read(&cpu_hotplug.puts_pending)) { - int delta; - - delta = atomic_xchg(&cpu_hotplug.puts_pending, 0); - cpu_hotplug.refcount -= delta; - } + apply_puts_pending(1); if (likely(!cpu_hotplug.refcount)) break; __set_current_state(TASK_UNINTERRUPTIBLE); -- 1.8.1.5