From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: David Miller <davem@davemloft.net>,
bpf@vger.kernel.org, netdev@vger.kernel.org,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Sebastian Sewior <bigeasy@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Clark Williams <williams@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Juri Lelli <juri.lelli@redhat.com>,
Ingo Molnar <mingo@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Vinicius Costa Gomes <vinicius.gomes@intel.com>,
Jakub Kicinski <kuba@kernel.org>
Subject: [patch V2 15/20] bpf: Provide recursion prevention helpers
Date: Thu, 20 Feb 2020 21:45:32 +0100 [thread overview]
Message-ID: <20200220204618.815084606@linutronix.de> (raw)
In-Reply-To: 20200220204517.863202864@linutronix.de
The places which need to prevent the execution of trace type BPF programs
to prevent deadlocks on the hash bucket lock do this open coded.
Provide two inline functions, bpf_disable/enable_instrumentation() to
replace these open coded protection constructs.
Use migrate_disable/enable() instead of preempt_disable/enable() right away
so this works on RT enabled kernels. On a !RT kernel migrate_disable /
enable() are mapped to preempt_disable/enable().
These helpers use this_cpu_inc/dec() instead of __this_cpu_inc/dec() on an
RT enabled kernel because migrate disabled regions are preemptible and
preemption might hit in the middle of a RMW operation which can lead to
inconsistent state.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: New patch. Use this_cpu_inc/dec() as pointed out by Mathieu.
---
include/linux/bpf.h | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -961,6 +961,36 @@ int bpf_prog_array_copy(struct bpf_prog_
#ifdef CONFIG_BPF_SYSCALL
DECLARE_PER_CPU(int, bpf_prog_active);
+/*
+ * Block execution of BPF programs attached to instrumentation (perf,
+ * kprobes, tracepoints) to prevent deadlocks on map operations as any of
+ * these events can happen inside a region which holds a map bucket lock
+ * and can deadlock on it.
+ *
+ * Use the preemption safe inc/dec variants on RT because migrate disable
+ * is preemptible on RT and preemption in the middle of the RMW operation
+ * might lead to inconsistent state. Use the raw variants for non RT
+ * kernels as migrate_disable() maps to preempt_disable() so the slightly
+ * more expensive save operation can be avoided.
+ */
+static inline void bpf_disable_instrumentation(void)
+{
+ migrate_disable();
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ this_cpu_inc(bpf_prog_active);
+ else
+ __this_cpu_inc(bpf_prog_active);
+}
+
+static inline void bpf_enable_instrumentation(void)
+{
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ this_cpu_dec(bpf_prog_active);
+ else
+ __this_cpu_dec(bpf_prog_active);
+ migrate_enable();
+}
+
extern const struct file_operations bpf_map_fops;
extern const struct file_operations bpf_prog_fops;
next prev parent reply other threads:[~2020-02-20 20:58 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 20:45 [patch V2 00/20] bpf: Make BPF and PREEMPT_RT co-exist Thomas Gleixner
2020-02-20 20:45 ` [patch V2 01/20] bpf: Enforce preallocation for all instrumentation programs Thomas Gleixner
2020-02-22 4:29 ` Alexei Starovoitov
2020-02-22 8:40 ` Thomas Gleixner
2020-02-23 22:40 ` Alexei Starovoitov
2020-02-22 16:44 ` kbuild test robot
2020-02-20 20:45 ` [patch V2 02/20] bpf: Update locking comment in hashtab code Thomas Gleixner
2020-02-20 20:45 ` [patch V2 03/20] bpf/tracing: Remove redundant preempt_disable() in __bpf_trace_run() Thomas Gleixner
2020-02-20 20:45 ` [patch V2 04/20] perf/bpf: Remove preempt disable around BPF invocation Thomas Gleixner
2020-02-20 20:45 ` [patch V2 05/20] bpf: Remove recursion prevention from rcu free callback Thomas Gleixner
2020-02-20 20:45 ` [patch V2 06/20] bpf: Dont iterate over possible CPUs with interrupts disabled Thomas Gleixner
2020-02-20 20:45 ` [patch V2 07/20] bpf: Provide bpf_prog_run_pin_on_cpu() helper Thomas Gleixner
2020-02-20 20:45 ` [patch V2 08/20] bpf: Replace cant_sleep() with cant_migrate() Thomas Gleixner
2020-02-20 20:45 ` [patch V2 09/20] bpf: Use bpf_prog_run_pin_on_cpu() at simple call sites Thomas Gleixner
2020-02-20 20:45 ` [patch V2 10/20] trace/bpf: Use migrate disable in trace_call_bpf() Thomas Gleixner
2020-02-20 20:45 ` [patch V2 11/20] bpf/tests: Use migrate disable instead of preempt disable Thomas Gleixner
2020-02-20 20:45 ` [patch V2 12/20] bpf: Use migrate_disable/enabe() in trampoline code Thomas Gleixner
2020-02-20 20:45 ` [patch V2 13/20] bpf: Use migrate_disable/enable in array macros and cgroup/lirc code Thomas Gleixner
2020-02-20 20:45 ` [patch V2 14/20] bpf: Use migrate_disable() in hashtab code Thomas Gleixner
2020-02-20 20:45 ` Thomas Gleixner [this message]
2020-02-20 20:45 ` [patch V2 16/20] bpf: Replace open coded recursion prevention Thomas Gleixner
2020-02-20 20:45 ` [patch V2 17/20] bpf: Factor out hashtab bucket lock operations Thomas Gleixner
2020-02-20 20:45 ` [patch V2 18/20] bpf: Prepare hashtab locking for PREEMPT_RT Thomas Gleixner
2020-02-20 20:45 ` [patch V2 19/20] bpf, lpm: Make locking RT friendly Thomas Gleixner
2020-02-20 20:45 ` [patch V2 20/20] bpf/stackmap: Dont trylock mmap_sem with PREEMPT_RT and interrupts disabled Thomas Gleixner
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=20200220204618.815084606@linutronix.de \
--to=tglx@linutronix.de \
--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=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=netdev@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=vinicius.gomes@intel.com \
--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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).