linux-kernel - [RFC 4/4] kprobe: remove preempt_disable() from check_kprobe_address

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Date:	Fri, 31 Jul 2015 19:08:08 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	tglx@...utronix.de,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [RFC 4/4] kprobe: remove preempt_disable() from check_kprobe_address_safe()

It should be safe to remove preempt_disable() here. It was introduced in
commit a189d0350f387 ("kprobes: disable preempt for module_text_address()
and kernel_text_address()") to protect against module removal. This is
however wrong (now) because the RCU list which is used requires a RCU
readlock. The comment in __module_text_address() has been updated and the
caller, too.
I *think* this preempt_disable() may go now.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 kernel/kprobes.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index a2d4e5164d7d..92d50ea83564 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1438,7 +1438,6 @@ static int check_kprobe_address_safe(struct kprobe *p,
 	if (ret)
 		return ret;
 	jump_label_lock();
-	preempt_disable();
 
 	/* Ensure it is not in reserved area nor out of text */
 	if (!kernel_text_address((unsigned long) p->addr) ||
@@ -1475,7 +1474,6 @@ static int check_kprobe_address_safe(struct kprobe *p,
 out_rcu_unlock:
 	rcu_read_unlock();
 out:
-	preempt_enable();
 	jump_label_unlock();
 
 	return ret;
-- 
2.4.6

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