BPF Archive on lore.kernel.org
 help / color / Atom feed
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	bpf <bpf@vger.kernel.org>, netdev <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Clark Williams <williams@redhat.com>,
	rostedt <rostedt@goodmis.org>, Juri Lelli <juri.lelli@redhat.com>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [RFC patch 14/19] bpf: Use migrate_disable() in hashtab code
Date: Wed, 19 Feb 2020 10:17:28 -0500 (EST)
Message-ID: <1127123648.641.1582125448879.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20200218233641.i7fyf36zxocgucap@ast-mbp>

----- On Feb 18, 2020, at 6:36 PM, Alexei Starovoitov alexei.starovoitov@gmail.com wrote:

[...]

> If I can use migrate_disable() without RT it will help my work on sleepable
> BPF programs. I would only have to worry about rcu_read_lock() since
> preempt_disable() is nicely addressed.

Hi Alexei,

You may want to consider using SRCU rather than RCU if you need to sleep while
holding a RCU read-side lock.

This is the synchronization approach I consider for adding the ability to take page
faults when doing syscall tracing.

Then you'll be able to replace preempt_disable() by combining SRCU and
migrate_disable():

AFAIU eBPF currently uses preempt_disable() for two reasons:

- Ensure the thread is not migrated,
  -> can be replaced by migrate_disable() in RT
- Provide RCU existence guarantee through sched-RCU
  -> can be replaced by SRCU, which allows sleeping and taking page faults.

I wonder if it would be acceptable to take a page fault while migration is
disabled though ?

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

  parent reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14 13:39 [RFC patch 00/19] bpf: Make BPF and PREEMPT_RT co-exist Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 01/19] sched: Provide migrate_disable/enable() inlines Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 02/19] sched: Provide cant_migrate() Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 03/19] bpf: Update locking comment in hashtab code Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 04/19] bpf/tracing: Remove redundant preempt_disable() in __bpf_trace_run() Thomas Gleixner
2020-02-19 16:54   ` Steven Rostedt
2020-02-19 17:26     ` Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 05/19] perf/bpf: Remove preempt disable around BPF invocation Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 06/19] bpf: Dont iterate over possible CPUs with interrupts disabled Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 07/19] bpf: Provide BPF_PROG_RUN_PIN_ON_CPU() macro Thomas Gleixner
2020-02-14 18:50   ` Mathieu Desnoyers
2020-02-14 19:36     ` Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 08/19] bpf: Replace cant_sleep() with cant_migrate() Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 09/19] bpf: Use BPF_PROG_RUN_PIN_ON_CPU() at simple call sites Thomas Gleixner
2020-02-19  1:39   ` Vinicius Costa Gomes
2020-02-19  9:00     ` Thomas Gleixner
2020-02-19 16:38       ` Alexei Starovoitov
2020-02-21  0:20       ` Kees Cook
2020-02-21 14:00         ` Thomas Gleixner
2020-02-21 14:05           ` Peter Zijlstra
2020-02-21 22:15           ` Kees Cook
2020-02-14 13:39 ` [RFC patch 10/19] trace/bpf: Use migrate disable in trace_call_bpf() Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 11/19] bpf/tests: Use migrate disable instead of preempt disable Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 12/19] bpf: Use migrate_disable/enabe() in trampoline code Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 13/19] bpf: Use migrate_disable/enable in array macros and cgroup/lirc code Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 14/19] bpf: Use migrate_disable() in hashtab code Thomas Gleixner
2020-02-14 19:11   ` Mathieu Desnoyers
2020-02-14 19:56     ` Thomas Gleixner
2020-02-18 23:36       ` Alexei Starovoitov
2020-02-19  0:49         ` Thomas Gleixner
2020-02-19  1:23           ` Alexei Starovoitov
2020-02-19 15:17         ` Mathieu Desnoyers [this message]
2020-02-20  4:19           ` Alexei Starovoitov
2020-02-14 13:39 ` [RFC patch 15/19] bpf: Use migrate_disable() in sys_bpf() Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 16/19] bpf: Factor out hashtab bucket lock operations Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 17/19] bpf: Prepare hashtab locking for PREEMPT_RT Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 18/19] bpf, lpm: Make locking RT friendly Thomas Gleixner
2020-02-14 13:39 ` [RFC patch 19/19] bpf/stackmap: Dont trylock mmap_sem with PREEMPT_RT and interrupts disabled Thomas Gleixner
2020-02-14 17:53 ` [RFC patch 00/19] bpf: Make BPF and PREEMPT_RT co-exist David Miller
2020-02-14 18:36   ` Thomas Gleixner
2020-02-17 12:59     ` [PATCH] bpf: Enforce map preallocation for all instrumentation programs Thomas Gleixner
2020-02-15 20:09 ` [RFC patch 00/19] bpf: Make BPF and PREEMPT_RT co-exist Jakub Kicinski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1127123648.641.1582125448879.JavaMail.zimbra@efficios.com \
    --to=mathieu.desnoyers@efficios.com \
    --cc=alexei.starovoitov@gmail.com \
    --cc=ast@kernel.org \
    --cc=bigeasy@linutronix.de \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=davem@davemloft.net \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=tglx@linutronix.de \
    --cc=williams@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org
	public-inbox-index bpf

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git