[V2][PATCH 2/5] oprofile: Fix crash when unloading module (hr timer mode)

[Robert Richter <robert.richter@amd.com>]

Oprofile may crash in a KVM guest while unlaoding modules. This
happens if oprofile_arch_init() fails and oprofile switches to the hr
timer mode as a fallback. In this case oprofile_arch_exit() is called,
but it never was initialized properly which causes the crash. This
patch fixes this.

oprofile: using timer interrupt.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
IP: [<ffffffff8123c226>] unregister_syscore_ops+0x41/0x58
PGD 41da3f067 PUD 41d80e067 PMD 0
Oops: 0002 [#1] PREEMPT SMP
CPU 5
Modules linked in: oprofile(-)

Pid: 2382, comm: modprobe Not tainted 3.1.0-rc7-00018-g709a39d #18 Advanced Micro Device Anaheim/Anaheim
RIP: 0010:[<ffffffff8123c226>]  [<ffffffff8123c226>] unregister_syscore_ops+0x41/0x58
RSP: 0018:ffff88041de1de98  EFLAGS: 00010296
RAX: 0000000000000000 RBX: ffffffffa00060e0 RCX: dead000000200200
RDX: 0000000000000000 RSI: dead000000100100 RDI: ffffffff8178c620
RBP: ffff88041de1dea8 R08: 0000000000000001 R09: 0000000000000082
R10: 0000000000000000 R11: ffff88041de1dde8 R12: 0000000000000080
R13: fffffffffffffff5 R14: 0000000000000001 R15: 0000000000610210
FS:  00007f9ae5bef700(0000) GS:ffff88042fd40000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000008 CR3: 000000041ca44000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process modprobe (pid: 2382, threadinfo ffff88041de1c000, task ffff88042db6d040)
Stack:
 ffff88041de1deb8 ffffffffa0006770 ffff88041de1deb8 ffffffffa000251e
 ffff88041de1dec8 ffffffffa00022c2 ffff88041de1ded8 ffffffffa0004993
 ffff88041de1df78 ffffffff81073115 656c69666f72706f 0000000000610200
Call Trace:
 [<ffffffffa000251e>] op_nmi_exit+0x15/0x17 [oprofile]
 [<ffffffffa00022c2>] oprofile_arch_exit+0xe/0x10 [oprofile]
 [<ffffffffa0004993>] oprofile_exit+0x13/0x15 [oprofile]
 [<ffffffff81073115>] sys_delete_module+0x1c3/0x22f
 [<ffffffff811bf09e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff8148070b>] system_call_fastpath+0x16/0x1b
Code: 20 c6 78 81 e8 c5 cc 23 00 48 8b 13 48 8b 43 08 48 be 00 01 10 00 00 00 ad de 48 b9 00 02 20 00 00 00 ad de 48 c7 c7 20 c6 78 81
 89 42 08 48 89 10 48 89 33 48 89 4b 08 e8 a6 c0 23 00 5a 5b
RIP  [<ffffffff8123c226>] unregister_syscore_ops+0x41/0x58
 RSP <ffff88041de1de98>
CR2: 0000000000000008
---[ end trace 06d4e95b6aa3b437 ]---

CC: stable@kernel.org # 2.6.37+
Signed-off-by: Robert Richter <robert.richter@amd.com>
---
 drivers/oprofile/oprof.c     |   29 ++++++++++++++++++++++++-----
 drivers/oprofile/timer_int.c |    1 +
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/drivers/oprofile/oprof.c b/drivers/oprofile/oprof.c
index dccd863..f8c752e 100644
--- a/drivers/oprofile/oprof.c
+++ b/drivers/oprofile/oprof.c
@@ -239,26 +239,45 @@ int oprofile_set_ulong(unsigned long *addr, unsigned long val)
 	return err;
 }
 
+static int timer_mode;
+
 static int __init oprofile_init(void)
 {
 	int err;
 
+	/* always init architecture to setup backtrace support */
 	err = oprofile_arch_init(&oprofile_ops);
-	if (err < 0 || timer) {
-		printk(KERN_INFO "oprofile: using timer interrupt.\n");
+
+	timer_mode = err || timer;	/* fall back to timer mode on errors */
+	if (timer_mode) {
+		if (!err)
+			oprofile_arch_exit();
 		err = oprofile_timer_init(&oprofile_ops);
 		if (err)
 			return err;
 	}
-	return oprofilefs_register();
+
+	err = oprofilefs_register();
+	if (!err)
+		return 0;
+
+	/* failed */
+	if (timer_mode)
+		oprofile_timer_exit();
+	else
+		oprofile_arch_exit();
+
+	return err;
 }
 
 
 static void __exit oprofile_exit(void)
 {
-	oprofile_timer_exit();
 	oprofilefs_unregister();
-	oprofile_arch_exit();
+	if (timer_mode)
+		oprofile_timer_exit();
+	else
+		oprofile_arch_exit();
 }
 
 
diff --git a/drivers/oprofile/timer_int.c b/drivers/oprofile/timer_int.c
index 3ef4462..878fba1 100644
--- a/drivers/oprofile/timer_int.c
+++ b/drivers/oprofile/timer_int.c
@@ -110,6 +110,7 @@ int oprofile_timer_init(struct oprofile_operations *ops)
 	ops->start = oprofile_hrtimer_start;
 	ops->stop = oprofile_hrtimer_stop;
 	ops->cpu_type = "timer";
+	printk(KERN_INFO "oprofile: using timer interrupt.\n");
 	return 0;
 }
 
-- 
1.7.7