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From: Alex Belits <abelits@marvell.com>
To: "frederic@kernel.org" <frederic@kernel.org>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>
Cc: "mingo@kernel.org" <mingo@kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Prasun Kapoor <pkapoor@marvell.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
	"linux-mm@vger.kernel.org" <linux-mm@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: [PATCH 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize
Date: Wed, 4 Mar 2020 16:14:28 +0000
Message-ID: <426ee885b89985f6bf348d64909eeb6a2cd83162.camel@marvell.com> (raw)
In-Reply-To: <4473787e1b6bc3cc226067e8d122092a678b63de.camel@marvell.com>

From: Yuri Norov <ynorov@marvell.com>

CPUs running isolated tasks are in userspace, so they don't have to
perform ring buffer updates immediately. If ring_buffer_resize()
schedules the update on those CPUs, isolation is broken. To prevent
that, updates for CPUs running isolated tasks are performed locally,
like for offline CPUs.

A race condition between this update and isolation breaking is avoided
at the cost of disabling per_cpu buffer writing for the time of update
when it coincides with isolation breaking.

Signed-off-by: Alex Belits <abelits@marvell.com>
---
 kernel/trace/ring_buffer.c | 61 ++++++++++++++++++++++++++++++++++----
 1 file changed, 55 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 61f0e92ace99..6c7479b6411d 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -21,6 +21,7 @@
 #include <linux/delay.h>
 #include <linux/slab.h>
 #include <linux/init.h>
+#include <linux/isolation.h>
 #include <linux/hash.h>
 #include <linux/list.h>
 #include <linux/cpu.h>
@@ -1701,6 +1702,37 @@ static void update_pages_handler(struct work_struct *work)
 	complete(&cpu_buffer->update_done);
 }
 
+static bool update_if_isolated(struct ring_buffer_per_cpu *cpu_buffer,
+			       int cpu)
+{
+	bool rv = false;
+
+	if (task_isolation_on_cpu(cpu)) {
+		/*
+		 * CPU is running isolated task. Since it may lose
+		 * isolation and re-enter kernel simultaneously with
+		 * this update, disable recording until it's done.
+		 */
+		atomic_inc(&cpu_buffer->record_disabled);
+		/* Make sure, update is done, and isolation state is current */
+		smp_mb();
+		if (task_isolation_on_cpu(cpu)) {
+			/*
+			 * If CPU is still running isolated task, we
+			 * can be sure that breaking isolation will
+			 * happen while recording is disabled, and CPU
+			 * will not touch this buffer until the update
+			 * is done.
+			 */
+			rb_update_pages(cpu_buffer);
+			cpu_buffer->nr_pages_to_update = 0;
+			rv = true;
+		}
+		atomic_dec(&cpu_buffer->record_disabled);
+	}
+	return rv;
+}
+
 /**
  * ring_buffer_resize - resize the ring buffer
  * @buffer: the buffer to resize.
@@ -1784,13 +1816,22 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
 			if (!cpu_buffer->nr_pages_to_update)
 				continue;
 
-			/* Can't run something on an offline CPU. */
+			/*
+			 * Can't run something on an offline CPU.
+			 *
+			 * CPUs running isolated tasks don't have to
+			 * update ring buffers until they exit
+			 * isolation because they are in
+			 * userspace. Use the procedure that prevents
+			 * race condition with isolation breaking.
+			 */
 			if (!cpu_online(cpu)) {
 				rb_update_pages(cpu_buffer);
 				cpu_buffer->nr_pages_to_update = 0;
 			} else {
-				schedule_work_on(cpu,
-						&cpu_buffer->update_pages_work);
+				if (!update_if_isolated(cpu_buffer, cpu))
+					schedule_work_on(cpu,
+					&cpu_buffer->update_pages_work);
 			}
 		}
 
@@ -1829,13 +1870,22 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
 
 		get_online_cpus();
 
-		/* Can't run something on an offline CPU. */
+		/*
+		 * Can't run something on an offline CPU.
+		 *
+		 * CPUs running isolated tasks don't have to update
+		 * ring buffers until they exit isolation because they
+		 * are in userspace. Use the procedure that prevents
+		 * race condition with isolation breaking.
+		 */
 		if (!cpu_online(cpu_id))
 			rb_update_pages(cpu_buffer);
 		else {
-			schedule_work_on(cpu_id,
+			if (!update_if_isolated(cpu_buffer, cpu_id))
+				schedule_work_on(cpu_id,
 					 &cpu_buffer->update_pages_work);
-			wait_for_completion(&cpu_buffer->update_done);
+				wait_for_completion(&cpu_buffer->update_done);
+			}
 		}
 
 		cpu_buffer->nr_pages_to_update = 0;
-- 
2.20.1


  parent reply index

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-04 16:01 [PATCH 00/12] "Task_isolation" mode Alex Belits
2020-03-04 16:03 ` [PATCH 01/12] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-03-04 16:04 ` [PATCH 02/12] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-03-04 16:07 ` [PATCH 03/12] task_isolation: userspace hard isolation from kernel Alex Belits
2020-03-05 18:33   ` Frederic Weisbecker
2020-03-08  5:32     ` [EXT] " Alex Belits
2020-04-28 14:12     ` Marcelo Tosatti
2020-03-06 15:26   ` Frederic Weisbecker
2020-03-08  6:06     ` [EXT] " Alex Belits
2020-03-06 16:00   ` Frederic Weisbecker
2020-03-08  7:16     ` [EXT] " Alex Belits
2020-03-04 16:08 ` [PATCH 04/12] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-03-04 16:09 ` [PATCH 05/12] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-03-04 16:10 ` [PATCH 06/12] task_isolation: arch/arm64: " Alex Belits
2020-03-04 16:31   ` Mark Rutland
2020-03-08  4:48     ` [EXT] " Alex Belits
2020-03-04 16:11 ` [PATCH 07/12] task_isolation: arch/arm: " Alex Belits
2020-03-04 16:12 ` [PATCH 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-03-06 16:03   ` Frederic Weisbecker
2020-03-08  7:28     ` [EXT] " Alex Belits
2020-03-09  2:38       ` Frederic Weisbecker
2020-03-04 16:13 ` [PATCH 09/12] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-03-04 16:14 ` Alex Belits [this message]
2020-03-04 16:15 ` [PATCH 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-03-06 15:34   ` Frederic Weisbecker
2020-03-08  6:48     ` [EXT] " Alex Belits
2020-03-09  2:28       ` Frederic Weisbecker
2020-03-04 16:16 ` [PATCH 12/12] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits
2020-03-08  3:42 ` [PATCH v2 00/12] "Task_isolation" mode Alex Belits
2020-03-08  3:44   ` [PATCH v2 01/12] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-03-08  3:46   ` [PATCH v2 02/12] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-03-08  3:47   ` [PATCH v2 03/12] task_isolation: userspace hard isolation from kernel Alex Belits
     [not found]     ` <20200307214254.7a8f6c22@hermes.lan>
2020-03-08  7:33       ` [EXT] " Alex Belits
2020-03-27  8:42     ` Marta Rybczynska
2020-04-06  4:31     ` Kevyn-Alexandre Paré
2020-04-06  4:43     ` Kevyn-Alexandre Paré
2020-03-08  3:48   ` [PATCH v2 04/12] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-03-08  3:49   ` [PATCH v2 05/12] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-03-08  3:50   ` [PATCH v2 06/12] task_isolation: arch/arm64: " Alex Belits
2020-03-09 16:59     ` Mark Rutland
2020-03-08  3:52   ` [PATCH v2 07/12] task_isolation: arch/arm: " Alex Belits
2020-03-08  3:53   ` [PATCH v2 08/12] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-03-08  3:54   ` [PATCH v2 09/12] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-03-08  3:55   ` [PATCH v2 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
2020-04-06  4:27     ` Kevyn-Alexandre Paré
2020-03-08  3:56   ` [PATCH v2 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-03-08  3:57   ` [PATCH v2 12/12] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits
2020-04-09 15:09   ` [PATCH v3 00/13] "Task_isolation" mode Alex Belits
2020-04-09 15:15     ` [PATCH 01/13] task_isolation: vmstat: add quiet_vmstat_sync function Alex Belits
2020-04-09 15:16     ` [PATCH 02/13] task_isolation: vmstat: add vmstat_idle function Alex Belits
2020-04-09 15:17     ` [PATCH v3 03/13] task_isolation: add instruction synchronization memory barrier Alex Belits
2020-04-15 12:44       ` Mark Rutland
2020-04-19  5:02         ` [EXT] " Alex Belits
2020-04-20 12:23           ` Will Deacon
2020-04-20 12:36             ` Mark Rutland
2020-04-20 13:55               ` Will Deacon
2020-04-21  7:41                 ` Will Deacon
2020-04-20 12:45           ` Mark Rutland
2020-04-09 15:20     ` [PATCH v3 04/13] task_isolation: userspace hard isolation from kernel Alex Belits
2020-04-09 18:00       ` Andy Lutomirski
2020-04-19  5:07         ` Alex Belits
2020-04-09 15:21     ` [PATCH 05/13] task_isolation: Add task isolation hooks to arch-independent code Alex Belits
2020-04-09 15:22     ` [PATCH 06/13] task_isolation: arch/x86: enable task isolation functionality Alex Belits
2020-04-09 15:23     ` [PATCH v3 07/13] task_isolation: arch/arm64: " Alex Belits
2020-04-22 12:08       ` Catalin Marinas
2020-04-09 15:24     ` [PATCH v3 08/13] task_isolation: arch/arm: " Alex Belits
2020-04-09 15:25     ` [PATCH v3 09/13] task_isolation: don't interrupt CPUs with tick_nohz_full_kick_cpu() Alex Belits
2020-04-09 15:26     ` [PATCH v3 10/13] task_isolation: net: don't flush backlog on CPUs running isolated tasks Alex Belits
2020-04-09 15:27     ` [PATCH v3 11/13] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
2020-04-09 15:27     ` [PATCH v3 12/13] task_isolation: kick_all_cpus_sync: don't kick isolated cpus Alex Belits
2020-04-09 15:28     ` [PATCH v3 13/13] task_isolation: CONFIG_TASK_ISOLATION prevents distribution of jobs to non-housekeeping CPUs Alex Belits

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