linux-kernel - [watchdog] 952c8813073: BUG: unable to handle kernel NULL pointer dereference at (null)

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Date:	Sat, 9 May 2015 20:50:54 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: [watchdog] 952c8813073: BUG: unable to handle kernel NULL pointer
 dereference at (null)

Hi Chris,

FYI, we noticed the below changes on

git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
commit 952c8813073ed240a610f8b44ecea9bdd60b62b4 ("watchdog: add watchdog_cpumask sysctl to assist nohz")


+------------------------------------------+------------+------------+
|                                          | ef15be37bb | 952c881307 |
+------------------------------------------+------------+------------+
| boot_successes                           | 10         | 0          |
| boot_failures                            | 0          | 22         |
| BUG:unable_to_handle_kernel              | 0          | 22         |
| Oops                                     | 0          | 22         |
| RIP:find_first_bit                       | 0          | 22         |
| Kernel_panic-not_syncing:Fatal_exception | 0          | 22         |
| backtrace:lockup_detector_init           | 0          | 22         |
| backtrace:kernel_init_freeable           | 0          | 22         |
+------------------------------------------+------------+------------+


[    0.073036] smpboot: CPU0: Intel QEMU Virtual CPU version 2.1.2 (fam: 06, model: 06, stepping: 03)
[    0.075023] Performance Events: Broken PMU hardware detected, using software events only.
[    0.077002] Failed to access perfctr msr (MSR c1 is 0)
[    0.079378] BUG: unable to handle kernel NULL pointer dereference at           (null)
[    0.080000] IP: [<ffffffff81432289>] find_first_bit+0x9/0x60
[    0.080000] PGD 0 
[    0.080000] Oops: 0000 [#1] SMP 
[    0.080000] Modules linked in:
[    0.080000] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.1.0-rc2-next-20150506 #1
[    0.080000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[    0.080000] task: ffff88013aba0000 ti: ffff88013aba8000 task.ti: ffff88013aba8000
[    0.080000] RIP: 0010:[<ffffffff81432289>]  [<ffffffff81432289>] find_first_bit+0x9/0x60
[    0.080000] RSP: 0000:ffff88013ababe68  EFLAGS: 00010202
[    0.080000] RAX: 00000000ee6b2800 RBX: 0000000000000004 RCX: 0000000000000018
[    0.080000] RDX: ffffffff821d7294 RSI: 0000000000000004 RDI: 0000000000000000
[    0.080000] RBP: ffff88013ababe68 R08: 0000000000000005 R09: 000000000000001f
[    0.080000] R10: 0000000039d63d7d R11: 000000000000001a R12: 0000000000000000
[    0.080000] R13: 00000000000027e0 R14: 0000000000000000 R15: 0000000000000000
[    0.080000] FS:  0000000000000000(0000) GS:ffff88013fc00000(0000) knlGS:0000000000000000
[    0.080000] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[    0.080000] CR2: 0000000000000000 CR3: 0000000001cb7000 CR4: 00000000000006f0
[    0.080000] Stack:
[    0.080000]  ffff88013ababe88 ffffffff81e8fee6 ffffffff821d7294 ffffffff81ff84a0
[    0.080000]  ffff88013ababf38 ffffffff81e690b8 0000000000000001 0000000000000000
[    0.080000]  0000000000000000 0000000000000000 0000000000000000 0000000000000000
[    0.080000] Call Trace:
[    0.080000]  [<ffffffff81e8fee6>] lockup_detector_init+0x33/0x79
[    0.080000]  [<ffffffff81e690b8>] kernel_init_freeable+0x128/0x248
[    0.080000]  [<ffffffff818bc4c0>] ? rest_init+0x90/0x90
[    0.080000]  [<ffffffff818bc4ce>] kernel_init+0xe/0xf0
[    0.080000]  [<ffffffff818d1aa2>] ret_from_fork+0x42/0x70
[    0.080000]  [<ffffffff818bc4c0>] ? rest_init+0x90/0x90
[    0.080000] Code: 66 90 48 83 c4 28 48 89 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 55 48 85 f6 48 89 e5 74 4b <48> 8b 0f 48 83 c7 08 ba 40 00 00 00 48 85 c9 74 19 eb 21 0f 1f 
[    0.080000] RIP  [<ffffffff81432289>] find_first_bit+0x9/0x60
[    0.080000]  RSP <ffff88013ababe68>
[    0.080000] CR2: 0000000000000000
[    0.080000] ---[ end trace afede291f6be7dba ]---
[    0.080000] Kernel panic - not syncing: Fatal exception

Thanks,
Fengguang Wu

View attachment "config-4.1.0-rc2-00070-g952c881" of type "text/plain" (129745 bytes)

View attachment ".dmesg" of type "text/plain" (33024 bytes)