linux-kernel - Re: [lkp-robot] [watchdog/softlockup] 4808e7a5dc: BUG:KASAN:null-ptr-deref_in

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Date:   Wed, 13 Jun 2018 10:27:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kernel test robot <xiaolong.ye@...el.com>
Cc:     mingo@...nel.org, oleg@...hat.com, gkohli@...eaurora.org,
        tglx@...utronix.de, mpe@...erman.id.au, bigeasy@...utronix.de,
        linux-kernel@...r.kernel.org, will.deacon@....com,
        dzickus@...hat.com, lkp@...org
Subject: Re: [lkp-robot] [watchdog/softlockup]  4808e7a5dc:
 BUG:KASAN:null-ptr-deref_in_h

On Wed, Jun 13, 2018 at 01:08:38PM +0800, kernel test robot wrote:
> [    0.037000] BUG: KASAN: null-ptr-deref in hrtimer_active+0x70/0xa0
> [    0.037000] Read of size 4 at addr 0000000000000010 by task swapper/1
> [    0.037000] 
> [    0.037000] CPU: 0 PID: 1 Comm: swapper Tainted: G                T 4.17.0-11348-g4808e7a #1
> [    0.037000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> [    0.037000] Call Trace:
> [    0.037000]  ? kasan_report+0xe3/0x360
> [    0.037000]  ? hrtimer_active+0x70/0xa0
> [    0.037000]  ? hrtimer_try_to_cancel+0x17/0x210
> [    0.037000]  ? hrtimer_cancel+0x15/0x20
> [    0.037000]  ? softlockup_stop_fn+0x11/0x20
> [    0.037000]  ? lockup_detector_reconfigure+0x25/0xa0
> [    0.037000]  ? lockup_detector_init+0x51/0x5d
> [    0.037000]  ? kernel_init_freeable+0xa9/0x243
> [    0.037000]  ? rest_init+0xd0/0xd0
> [    0.037000]  ? kernel_init+0xf/0x120
> [    0.037000]  ? rest_init+0xd0/0xd0
> [    0.037000]  ? ret_from_fork+0x24/0x30

ARGH, I thought I fixed that one..

I think that'll cure things, but let me do a KASAN build myself.

--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -587,8 +587,8 @@ static __init void lockup_detector_setup
 		return;
 
 	mutex_lock(&watchdog_mutex);
-	softlockup_initialized = true;
 	lockup_detector_reconfigure();
+	softlockup_initialized = true;
 	mutex_unlock(&watchdog_mutex);
 }