linux-kernel - [RFC PATCH -tip 9/9] tracing: kprobes: Fix to not enabling preemption

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Date:   Fri,  9 Mar 2018 21:39:45 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Cc:     x86@...nel.org, Masami Hiramatsu <mhiramat@...nel.org>,
        Yang Bo <yangbo@...pin.com>, Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Laura Abbott <labbott@...hat.com>, Josef Bacik <jbacik@...com>,
        Alexei Starovoitov <ast@...nel.org>
Subject: [RFC PATCH -tip 9/9] tracing: kprobes: Fix to not enabling preemption

Since kprobes pre_handler doesn't need to recover preemption
even if it modifies regs->ip anymore, this fixes to remove
the preempt_enable_no_resched() from pre_handler.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/trace/trace_kprobe.c |    3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 5ce9b8cf7be3..6c894e2be8d6 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1221,12 +1221,9 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
 		 * We need to check and see if we modified the pc of the
 		 * pt_regs, and if so clear the kprobe and return 1 so that we
 		 * don't do the single stepping.
-		 * The ftrace kprobe handler leaves it up to us to re-enable
-		 * preemption here before returning if we've modified the ip.
 		 */
 		if (orig_ip != instruction_pointer(regs)) {
 			reset_current_kprobe();
-			preempt_enable_no_resched();
 			return 1;
 		}
 		if (!ret)