linux-kernel - [PATCH]Fix the order of atomic operations in restore_previous

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Date:	Fri, 18 Jan 2008 11:20:46 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	tony.luck@...el.com, Shaohua Li <shaohua.li@...el.com>
CC:	ia64 <linux-ia64@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: [PATCH]Fix the order of atomic operations in restore_previous_kprobes
 on ia64

From: Masami Hiramatsu <mhiramat@...hat.com>

Fix the order of atomic operations to prevent overwriting prev_kprobe[0].
To pop values from stack, we must decrement stack index right AFTER
reading values.

Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
---
Details of this issue was reported to
http://sources.redhat.com/bugzilla/show_bug.cgi?id=2071

   arch/ia64/kernel/kprobes.c |    7 ++++---
   1 file changed, 4 insertions(+), 3 deletions(-)

Index: 2.6.24-rc8/arch/ia64/kernel/kprobes.c
===================================================================
--- 2.6.24-rc8.orig/arch/ia64/kernel/kprobes.c	2008-01-17 21:14:01.000000000 -0500
+++ 2.6.24-rc8/arch/ia64/kernel/kprobes.c	2008-01-17 21:14:01.000000000 -0500
@@ -381,9 +381,10 @@
   static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
   {
   	unsigned int i;
-	i = atomic_sub_return(1, &kcb->prev_kprobe_index);
-	__get_cpu_var(current_kprobe) = kcb->prev_kprobe[i].kp;
-	kcb->kprobe_status = kcb->prev_kprobe[i].status;
+	i = atomic_read(&kcb->prev_kprobe_index);
+	__get_cpu_var(current_kprobe) = kcb->prev_kprobe[i-1].kp;
+	kcb->kprobe_status = kcb->prev_kprobe[i-1].status;
+	atomic_sub(1, &kcb->prev_kprobe_index);
   }

   static void __kprobes set_current_kprobe(struct kprobe *p,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com, masami.hiramatsu.pt@...achi.com


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