linux-kernel - [patch V3 06/22] bpf/trace: Remove redundant preempt_disable from trace_call

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Message-Id: <20200224145643.059995527@linutronix.de>
Date:   Mon, 24 Feb 2020 15:01:37 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     David Miller <davem@...emloft.net>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Sebastian Sewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Clark Williams <williams@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: [patch V3 06/22] bpf/trace: Remove redundant preempt_disable from trace_call_bpf()

Similar to __bpf_trace_run this is redundant because __bpf_trace_run() is
invoked from a trace point via __DO_TRACE() which already disables
preemption _before_ invoking any of the functions which are attached to a
trace point.

Remove it and add a cant_sleep() check.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
V3: New patch. Replaces the previous one which converted this to migrate_disable() 
---
 kernel/trace/bpf_trace.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -83,7 +83,7 @@ unsigned int trace_call_bpf(struct trace
 	if (in_nmi()) /* not supported yet */
 		return 1;
 
-	preempt_disable();
+	cant_sleep();
 
 	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) {
 		/*
@@ -115,7 +115,6 @@ unsigned int trace_call_bpf(struct trace
 
  out:
 	__this_cpu_dec(bpf_prog_active);
-	preempt_enable();
 
 	return ret;
 }