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) [thread overview]
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
next prev parent reply other threads:[~2020-02-19 15:17 UTC|newest]
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
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