linux-kernel - i915_do_wait_request BUG: unable to handle kernel NULL pointer dereference at (null)

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Message-ID: <u2nc4e36d111004230324x7e19b794ifbf1ae3cc157ab2e@mail.gmail.com>
Date:	Fri, 23 Apr 2010 12:24:25 +0200
From:	Zdenek Kabelac <zdenek.kabelac@...il.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	eric@...olt.net, Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: i915_do_wait_request BUG: unable to handle kernel NULL pointer 
	dereference at (null)

Hi

Just tried to boot current vanilla upstream kernel - and got pretty ugly  oops.
Here is serial console catch after X-startup:


BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffffa035de81>] i915_do_wait_request+0x101/0x4f0 [i915]
PGD 139649067 PUD 133b5a067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
last sysfs file: /sys/devices/virtual/backlight/acpi_video0/actual_brightness
CPU 0
Modules linked in: xt_tcpudp bridge stp llc autofs4 sunrpc ipv6
ipt_REJECT xt_physdev xt_state ]

Pid: 2725, comm: X Not tainted 2.6.34-rc5-00131-g4424503 #63 6464CTO/6464CTO
RIP: 0010:[<ffffffffa035de81>] [<ffffffffa035de81>]
i915_do_wait_request+0x101/0x4f0 [i915]
RSP: 0018:ffff880139923a88 EFLAGS: 00010246
RAX: ffffffffa0383e5e RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000002 RDI: ffff88013965a000
RBP: ffff880139923af8 R08: 0000000000000002 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88013965a000
R13: 0000000000000002 R14: ffff8801364b4000 R15: 0000000000071184
FS: 00007f76aac81840(0000) GS:ffff880002600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000133bdd000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process X (pid: 2725, threadinfo ffff880139922000, task ffff88013991c640)
Stack:
ffff8801364b5218 ffff880132482250 ffff880139923ab8 ffff880135292540
<0> 0000000000000002 ffff88013965a000 0000000000071188 0000000000071184
<0> ffff880139923af8 ffff880135292540 ffff880135292780 ffff88013965a000
Call Trace:
[<ffffffffa035fb7f>] i915_gem_object_set_to_display_plane+0xbf/0x130 [i915]
[<ffffffffa036ef28>] intel_pipe_set_base+0x118/0x4b0 [i915]
[<ffffffffa034a69c>] drm_crtc_helper_set_config+0x75c/0x8f0 [drm_kms_helper]
[<ffffffffa0327e1f>] drm_mode_setcrtc+0x2af/0x3b0 [drm]
[<ffffffffa03199ca>] drm_ioctl+0x33a/0x4a0 [drm]
[<ffffffffa0327b70>] ? drm_mode_setcrtc+0x0/0x3b0 [drm]
[<ffffffff8113d05d>] vfs_ioctl+0x3d/0xf0
[<ffffffff8113d624>] do_vfs_ioctl+0x84/0x5b0
[<ffffffff8112e255>] ? fget_light+0x75/0x290
[<ffffffff8100310c>] ? sysret_check+0x27/0x62
[<ffffffff8113dbd1>] sys_ioctl+0x81/0xa0
[<ffffffff810030db>] system_call_fastpath+0x16/0x1b
Code: 86 fb ff ff 89 d8 4c 8b 65 e0 48 8b 5d d8 4c 8b 6d e8 4c 8b 75
f0 4c 8b 7d f8 c9 c3 66 0f
RIP [<ffffffffa035de81>] i915_do_wait_request+0x101/0x4f0 [i915]
RSP <ffff880139923a88>
CR2: 0000000000000000
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffffa035cb27>] i915_get_gem_seqno+0x37/0x40 [i915]



Looks like problematic commit is e552eb7038a36d9b18860f525aa02875e313fe16
Which changes i915_get_gem_seqno()   to access (dev_priv->seqno_page)[0]


	if (IS_I965G(dev))
		return ((volatile u32 *)(dev_priv->seqno_page))[0];
00000000000013e8 <i915_do_wait_request+0xf8> mov    0x88(%r14),%rcx
	BUG_ON(seqno == 0);

	if (atomic_read(&dev_priv->mm.wedged))
		return -EIO;

	if (!i915_seqno_passed(i915_get_gem_seqno(dev), seqno)) {
00000000000013ef <i915_do_wait_request+0xff> xor    %ebx,%ebx
i915_get_gem_seqno(struct drm_device *dev)
{
	drm_i915_private_t *dev_priv = dev->dev_private;

	if (IS_I965G(dev))
		return ((volatile u32 *)(dev_priv->seqno_page))[0];
00000000000013f1 <i915_do_wait_request+0x101> mov    (%rcx),%ecx
	BUG_ON(seqno == 0);

	if (atomic_read(&dev_priv->mm.wedged))
		return -EIO;

	if (!i915_seqno_passed(i915_get_gem_seqno(dev), seqno)) {

my hw: T61, 4GB,  x86_64

Bye

Zdenek
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