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    Subject[PATCH 154/270] drm/i915: remove useless BUG_ON which caused a regression in 3.5.
    Date
    3.5.7u1 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Willy Tarreau <w@1wt.eu>

    commit c77d7162a7ae451c2e895d7ef7fbeb0906107472 upstream.

    starting an old X server causes a kernel BUG since commit 1b50247a8d:

    ------------[ cut here ]------------
    kernel BUG at drivers/gpu/drm/i915/i915_gem.c:3661!
    invalid opcode: 0000 [#1] SMP
    Modules linked in: snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss uvcvideo
    +videobuf2_core videodev videobuf2_vmalloc videobuf2_memops uhci_hcd ath9k mac80211 snd_hda_codec_realtek ath9k_common microcode
    +ath9k_hw psmouse serio_raw sg ath cfg80211 atl1c lpc_ich mfd_core ehci_hcd snd_hda_intel snd_hda_codec snd_hwdep snd_pcm rtc_cmos
    +snd_timer snd evdev eeepc_laptop snd_page_alloc sparse_keymap

    Pid: 2866, comm: X Not tainted 3.5.6-rc1-eeepc #1 ASUSTeK Computer INC. 1005HA/1005HA
    EIP: 0060:[<c12dc291>] EFLAGS: 00013297 CPU: 0
    EIP is at i915_gem_entervt_ioctl+0xf1/0x110
    EAX: f5941df4 EBX: f5940000 ECX: 00000000 EDX: 00020000
    ESI: f5835400 EDI: 00000000 EBP: f51d7e38 ESP: f51d7e20
    DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
    CR0: 8005003b CR2: b760e0a0 CR3: 351b6000 CR4: 000007d0
    DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
    DR6: ffff0ff0 DR7: 00000400
    Process X (pid: 2866, ti=f51d6000 task=f61af8d0 task.ti=f51d6000)
    Stack:
    00000001 00000000 f5835414 f51d7e84 f5835400 f54f85c0 f51d7f10 c12b530b
    00000001 c151b139 c14751b6 c152e030 00000b32 00006459 00000059 0000e200
    00000001 00000000 00006459 c159ddd0 c12dc1a0 ffffffea 00000000 00000000
    Call Trace:
    [<c12b530b>] drm_ioctl+0x2eb/0x440
    [<c12dc1a0>] ? i915_gem_init+0xe0/0xe0
    [<c1052b2b>] ? enqueue_hrtimer+0x1b/0x50
    [<c1053321>] ? __hrtimer_start_range_ns+0x161/0x330
    [<c10530b3>] ? lock_hrtimer_base+0x23/0x50
    [<c1053163>] ? hrtimer_try_to_cancel+0x33/0x70
    [<c12b5020>] ? drm_version+0x90/0x90
    [<c10ca171>] vfs_ioctl+0x31/0x50
    [<c10ca2e4>] do_vfs_ioctl+0x64/0x510
    [<c10535de>] ? hrtimer_nanosleep+0x8e/0x100
    [<c1052c20>] ? update_rmtp+0x80/0x80
    [<c10ca7c9>] sys_ioctl+0x39/0x60
    [<c1433949>] syscall_call+0x7/0xb
    Code: 83 c4 0c 5b 5e 5f 5d c3 c7 44 24 04 2c 05 53 c1 c7 04 24 6f ef 47 c1 e8 6e e0 fd ff c7 83 38 1e 00 00 00 00 00 00 e9 3f ff ff
    +ff <0f> 0b eb fe 0f 0b eb fe 8d b4 26 00 00 00 00 0f 0b eb fe 8d b6
    EIP: [<c12dc291>] i915_gem_entervt_ioctl+0xf1/0x110 SS:ESP 0068:f51d7e20
    ---[ end trace dd332ec083cbd513 ]---

    The crash happens here in i915_gem_entervt_ioctl() :

    3659 BUG_ON(!list_empty(&dev_priv->mm.active_list));
    3660 BUG_ON(!list_empty(&dev_priv->mm.flushing_list));
    -> 3661 BUG_ON(!list_empty(&dev_priv->mm.inactive_list));
    3662 mutex_unlock(&dev->struct_mutex);

    Quoting Chris :
    "That BUG_ON there is silly and can simply be removed. The check is to
    verify that no batches were submitted to the kernel whilst the UMS/GEM
    client was suspended - to which the BUG_ONs are a crude approximation.
    Furthermore, the checks are too late, since it means we attempted to
    program the hardware whilst it was in an invalid state, the BUG_ONs are
    the least of your concerns at that point."

    Note that this regression has been introduced in

    commit 1b50247a8ddde4af5aaa0e6bc125615372ce6c16
    Author: Chris Wilson <chris@chris-wilson.co.uk>
    Date: Tue Apr 24 15:47:30 2012 +0100

    drm/i915: Remove the list of pinned inactive objects

    Cc: Chris Wilson <chris@chris-wilson.co.uk>
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    [danvet: Added note about the regressing commit and cc: stable.]
    Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    [herton: adjusted context]
    Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
    ---
    drivers/gpu/drm/i915/i915_gem.c | 1 -
    1 file changed, 1 deletion(-)

    diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
    index 35926ad..fc6683a 100644
    --- a/drivers/gpu/drm/i915/i915_gem.c
    +++ b/drivers/gpu/drm/i915/i915_gem.c
    @@ -3658,7 +3658,6 @@ i915_gem_entervt_ioctl(struct drm_device *dev, void *data,

    BUG_ON(!list_empty(&dev_priv->mm.active_list));
    BUG_ON(!list_empty(&dev_priv->mm.flushing_list));
    - BUG_ON(!list_empty(&dev_priv->mm.inactive_list));
    mutex_unlock(&dev->struct_mutex);

    ret = drm_irq_install(dev);
    --
    1.7.9.5


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