From: "Kevyn-Alexandre Paré" <kapare@posteo.net>
To: Alex Belits <abelits@marvell.com>
Cc: "frederic@kernel.org" <frederic@kernel.org>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
"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>,
"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"davem@davemloft.net" <davem@davemloft.net>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"will@kernel.org" <will@kernel.org>
Subject: Re: [PATCH v2 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize
Date: Mon, 6 Apr 2020 00:27:09 -0400 [thread overview]
Message-ID: <20200406042709.e4isjrvrrwsusjc4@x1> (raw)
In-Reply-To: <5add46d3bfbdac3fb42dcef6b6e4ea0e39abe11f.camel@marvell.com>
On Sun, Mar 08, 2020 at 03:55:24AM +0000, Alex Belits wrote:
> 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: Yuri Norov <ynorov@marvell.com>
> [abelits@marvell.com: updated to prevent race with isolation breaking]
> Signed-off-by: Alex Belits <abelits@marvell.com>
> ---
> kernel/trace/ring_buffer.c | 62 ++++++++++++++++++++++++++++++++++----
> 1 file changed, 56 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 61f0e92ace99..593effe40183 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;
gcc output:
kernel/trace/ring_buffer.c: In function 'ring_buffer_resize':
kernel/trace/ring_buffer.c:1884:4: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
if (!update_if_isolated(cpu_buffer, cpu_id))
^~
kernel/trace/ring_buffer.c:1887:5: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
wait_for_completion(&cpu_buffer->update_done);
^~~~~~~~~~~~~~~~~~~
kernel/trace/ring_buffer.c:1858:4: error: label 'out' used but not defined
goto out;
^~~~
kernel/trace/ring_buffer.c:1868:4: error: label 'out_err' used but not defined
goto out_err;
^~~~
My fix:
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 593effe40183..8b458400ac31 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1881,9 +1881,8 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
if (!cpu_online(cpu_id))
rb_update_pages(cpu_buffer);
else {
- if (!update_if_isolated(cpu_buffer, cpu_id))
- schedule_work_on(cpu_id,
- &cpu_buffer->update_pages_work);
+ 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);
}
}
thx,
-- Kevyn-Alexandre Paré
next prev parent reply other threads:[~2020-04-06 4:27 UTC|newest]
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 ` [PATCH 10/12] task_isolation: ringbuffer: don't interrupt CPUs running isolated tasks on buffer resize Alex Belits
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 [this message]
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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