linux-kernel - [tip:perf/core] Revert "kprobes: Warn if optprobe handler tries to change execution path"

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Date:   Wed, 18 Oct 2017 09:22:40 -0700
From:   "tip-bot for Naveen N. Rao" <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, mingo@...nel.org,
        peterz@...radead.org, hpa@...or.com, mpe@...erman.id.au,
        tglx@...utronix.de, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org, ananth@...ux.vnet.ibm.com,
        naveen.n.rao@...ux.vnet.ibm.com
Subject: [tip:perf/core] Revert "kprobes: Warn if optprobe handler tries to
 change execution path"

Commit-ID:  4f3a871443669c6b4d458a60ac8d8ca5eedc3f97
Gitweb:     https://git.kernel.org/tip/4f3a871443669c6b4d458a60ac8d8ca5eedc3f97
Author:     Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
AuthorDate: Tue, 17 Oct 2017 13:48:34 +0530
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 18 Oct 2017 15:21:35 +0200

Revert "kprobes: Warn if optprobe handler tries to change execution path"

This reverts commit:

  e863d539614641 ("kprobes: Warn if optprobe handler tries to change execution path")

On PowerPC, we place a probe at kretprobe_trampoline to catch function
returns and with CONFIG_OPTPROBES=y, this probe gets optimized. This
works for us due to the way we handle the optprobe as described in
commit:

  762df10bad6954 ("powerpc/kprobes: Optimize kprobe in kretprobe_trampoline()")

With the above commit, we end up with a warning. As such, revert this change.

Reported-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20171017081834.3629-1-naveen.n.rao@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/kprobes.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 2d28377..15fba7f 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -387,10 +387,7 @@ void opt_pre_handler(struct kprobe *p, struct pt_regs *regs)
 	list_for_each_entry_rcu(kp, &p->list, list) {
 		if (kp->pre_handler && likely(!kprobe_disabled(kp))) {
 			set_kprobe_instance(kp);
-			if (kp->pre_handler(kp, regs)) {
-				if (WARN_ON_ONCE(1))
-					pr_err("Optprobe ignores instruction pointer changing.(%pF)\n", p->addr);
-			}
+			kp->pre_handler(kp, regs);
 		}
 		reset_kprobe_instance();
 	}