# help: dracut null pointer exception

## fpemud

when I use genkernel, the boot process is normal.

but when I switch to dracut, sometimes the PC can boot and sometimes can not, and there's alwasys exceptions in the dmesg.

I switch on the dracut debug switch, but I found all the exceptions are before the first dracut debug output.

How to attach file in this forum  :Exclamation:   :Question: 

Here's the first exception:

```
IOMMU: Prepare 0-16MiB unity mapping for LPC

IOMMU: Setting identity map for device 0000:00:1f.0 [0x0 - 0xffffff]

PCI-DMA: Intel(R) Virtualization Technology for Directed I/O

Simple Boot Flag at 0x51 set to 0x1

BUG: unable to handle kernel NULL pointer dereference at           (null)

IP: [<ffffffff81058a2c>] futex_wake+0x76/0x103

PGD 74814067 PUD 74818067 PMD 0 

Oops: 0000 [#1] PREEMPT SMP 

CPU 1 

Modules linked in:

Pid: 367, comm: udevadm Not tainted 3.2.12-gentoo #2 ASUSTeK Computer Inc.         UL30VT              /UL30VT    

RIP: 0010:[<ffffffff81058a2c>]  [<ffffffff81058a2c>] futex_wake+0x76/0x103

RSP: 0018:ffff88007480fd78  EFLAGS: 00010297

RAX: ffffffff814f81c8 RBX: ffffffff814f81c0 RCX: 000000007c10d3bd

RDX: 0000000000000000 RSI: 00000000a2dd87bf RDI: ffffffffffffffe8

RBP: ffff88007480fdd8 R08: 00000000364cbeb0 R09: 0000000000000000

R10: 00000000004024f8 R11: 0000000000000202 R12: 00000000ffffffff

R13: 0000000000000001 R14: 0000000000000000 R15: 000000005ccc8740

FS:  00007f7d5ccc8740(0000) GS:ffff880079b00000(0000) knlGS:0000000000000000

CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b

CR2: 0000000000000000 CR3: 00000000758c6000 CR4: 00000000000406e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400

Process udevadm (pid: 367, threadinfo ffff88007480e000, task ffff880075886450)

Stack:

 000000000000000e ffffffff814f81c8 00007fffc178d000 ffff880074810000

 000000000000051c ffff8800743264e0 ffff880074810000 0000000000000000

 0000000001f25bc2 00007fffc178d51c 0000000000000000 000000005ccc8740

Call Trace:

 [<ffffffff8105a34c>] do_futex+0xa7/0x944

 [<ffffffff810a97b2>] ? handle_mm_fault+0x21c/0x231

 [<ffffffff810ebfe1>] ? mntput+0x21/0x23

 [<ffffffff810c37fd>] ? kmem_cache_free+0x88/0x8d

 [<ffffffff8105ad13>] sys_futex+0x12a/0x13b

 [<ffffffff812dd4fb>] system_call_fastpath+0x16/0x1b

Code: 89 c6 0f 85 9e 00 00 00 48 89 df e8 db f6 ff ff 48 89 c3 48 89 c7 e8 14 3e 28 00 48 8b 7b 08 48 8d 43 08 48 89 45 a8 48 83 ef 18 <4c> 8b 7f 18 49 83 ef 18 eb 4e 48 83 ff c8 74 3d 48 8b 45 b0 48 

RIP  [<ffffffff81058a2c>] futex_wake+0x76/0x103

 RSP <ffff88007480fd78>

CR2: 0000000000000000

BUG: unable to handle kernel 

---[ end trace fe4ebffb2b8ff187 ]---

```

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## gr0sshirn

I am fighting against the same problem. Did you found a solution?

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## thumper

I tried genkernel with the same config I've been using with dracut and seem to have a similar problem, but the oops looks different.

```
[    0.699974] Trying to unpack rootfs image as initramfs...

[    1.109639] Freeing initrd memory: 29920K (ffff8800362b8000 - ffff880037ff0000)

[    1.110364] BUG: unable to handle kernel NULL pointer dereference at           (null)

[    1.110461] IP: [<ffffffff810c2cd7>] futex_wake+0x77/0x130

[    1.110528] PGD 235fb4067 PUD 235fa7067 PMD 0 

[    1.110648] Oops: 0000 [#1] SMP 

[    1.110739] Modules linked in:

[    1.110802] CPU: 0 PID: 45 Comm: modprobe Not tainted 3.11.3-gentoo #3

[    1.110837] Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./970A-D3P, BIOS F5 08/06/2013

[    1.110874] task: ffff880235d1aee0 ti: ffff880235fa4000 task.ti: ffff880235fa4000

[    1.110910] RIP: 0010:[<ffffffff810c2cd7>]  [<ffffffff810c2cd7>] futex_wake+0x77/0x130

[    1.110977] RSP: 0018:ffff880235fa5da8  EFLAGS: 00010246

[    1.111011] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 000000009e944f0f

[    1.111044] RDX: 0000000000000000 RSI: 00000000e2671e7f RDI: ffffffff81ef2b50

[    1.111078] RBP: ffff880235fa5e08 R08: 00000000cedd2fdc R09: 0000000000000000

[    1.111112] R10: 00007fe85a6ebb20 R11: 0000000000000202 R12: 0000000000000000

[    1.111146] R13: ffffffff81ef2b50 R14: 00000000ffffffff R15: ffffffff81ef2b58

[    1.111180] FS:  00007fe85a6e7700(0000) GS:ffff88023fc00000(0000) knlGS:0000000000000000

[    1.111216] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033

[    1.111249] CR2: 0000000000000000 CR3: 000000022f4da000 CR4: 00000000000007f0

[    1.111283] Stack:

[    1.111354]  ffff880235fa5df8 000000015a6eb000 ffff880200000001 00007fff7a8e9000

[    1.111509]  ffff880235f98e00 00000000000005d8 ffff880235fa5ea8 0000000000000001

[    1.111661]  0000000000000001 0000000000000000 00007fff7a8e95d8 0000000000000000

[    1.111813] Call Trace:

[    1.111847]  [<ffffffff810c4f21>] do_futex+0x101/0xa70

[    1.111883]  [<ffffffff8101b3d3>] ? native_sched_clock+0x13/0x80

[    1.111917]  [<ffffffff8110544c>] ? acct_account_cputime+0x1c/0x20

[    1.111953]  [<ffffffff810988e6>] ? account_user_time+0xa6/0xc0

[    1.111988]  [<ffffffff810c5928>] SyS_futex+0x98/0x1a0

[    1.112022]  [<ffffffff810206a5>] ? syscall_trace_enter+0x25/0x240

[    1.112058]  [<ffffffff8165e06f>] tracesys+0xe1/0xe6

[    1.112091] Code: a0 fc ff ff 85 c0 41 89 c4 0f 85 b0 00 00 00 48 8d 7d b8 e8 bc fb ff ff 49 89 c5 48 89 c7 e8 61 25 59 00 49 8b 45 08 4d 8d 7d 08 <48> 8b 18 48 8d 78 e8 48 83 eb 18 49 39 c7 75 20 eb 67 0f 1f 80 

[    1.114100] RIP  [<ffffffff810c2cd7>] futex_wake+0x77/0x130

[    1.114163]  RSP <ffff880235fa5da8>

[    1.114195] CR2: 0000000000000000

[    1.114238] ---[ end trace 54044e6ca93e3ad4 ]---

[    1.114690] AMD-Vi: Found IOMMU at 0000:00:00.2 cap 0x40
```

So I too and interested in finding the root cause of the problem.

George

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## gr0sshirn

https://bugzilla.kernel.org/show_bug.cgi?id=65661

https://bugs.gentoo.org/show_bug.cgi?id=462928

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## gr0sshirn

Changing from (e)udev to systemd solves the problem!  :Smile: 

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