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    Subject[137/264] fb: avoid possible deadlock caused by fb_set_suspend
    3.1-stable review patch.  If anyone has any objections, please let me know.


    From: Herton Ronaldo Krzesinski <>

    commit 9e769ff3f585db8f978f9113be83d36c7e3965dd upstream.

    A lock ordering issue can cause deadlocks: in framebuffer/console code,
    all needed struct fb_info locks are taken before acquire_console_sem(),
    in places which need to take console semaphore.

    But fb_set_suspend is always called with console semaphore held, and
    inside it we call lock_fb_info which gets the fb_info lock, inverse
    locking order of what the rest of the code does. This causes a real
    deadlock issue, when we write to state fb sysfs attribute (which calls
    fb_set_suspend) while a framebuffer is being unregistered by
    remove_conflicting_framebuffers, as can be shown by following show
    blocked state trace on a test program which loads i915 and runs another
    forked processes writing to state attribute:

    Test process with semaphore held and trying to get fb_info lock:
    fb-test2 D 0000000000000000 0 237 228 0x00000000
    ffff8800774f3d68 0000000000000082 00000000000135c0 00000000000135c0
    ffff880000000000 ffff8800774f3fd8 ffff8800774f3fd8 ffff880076ee4530
    00000000000135c0 ffff8800774f3fd8 ffff8800774f2000 00000000000135c0
    Call Trace:
    [<ffffffff8141287a>] __mutex_lock_slowpath+0x11a/0x1e0
    [<ffffffff814142f2>] ? _raw_spin_lock_irq+0x22/0x40
    [<ffffffff814123d3>] mutex_lock+0x23/0x50
    [<ffffffff8125dfc5>] lock_fb_info+0x25/0x60
    [<ffffffff8125e3f0>] fb_set_suspend+0x20/0x80
    [<ffffffff81263e2f>] store_fbstate+0x4f/0x70
    [<ffffffff812e7f70>] dev_attr_store+0x20/0x30
    [<ffffffff811c46b4>] sysfs_write_file+0xd4/0x160
    [<ffffffff81155a26>] vfs_write+0xc6/0x190
    [<ffffffff81155d51>] sys_write+0x51/0x90
    [<ffffffff8100c012>] system_call_fastpath+0x16/0x1b
    modprobe process stalled because has the fb_info lock (got inside
    unregister_framebuffer) but waiting for the semaphore held by the
    test process which is waiting to get the fb_info lock:
    modprobe D 0000000000000000 0 230 218 0x00000000
    ffff880077a4d618 0000000000000082 0000000000000001 0000000000000001
    ffff880000000000 ffff880077a4dfd8 ffff880077a4dfd8 ffff8800775a2e20
    00000000000135c0 ffff880077a4dfd8 ffff880077a4c000 00000000000135c0
    Call Trace:
    [<ffffffff81411fe5>] schedule_timeout+0x215/0x310
    [<ffffffff81058051>] ? get_parent_ip+0x11/0x50
    [<ffffffff814130dd>] __down+0x6d/0xb0
    [<ffffffff81089f71>] down+0x41/0x50
    [<ffffffff810629ac>] acquire_console_sem+0x2c/0x50
    [<ffffffff812ca53d>] unbind_con_driver+0xad/0x2d0
    [<ffffffff8126f5f7>] fbcon_event_notify+0x457/0x890
    [<ffffffff814144ff>] ? _raw_spin_unlock_irqrestore+0x1f/0x50
    [<ffffffff81058051>] ? get_parent_ip+0x11/0x50
    [<ffffffff8141836d>] notifier_call_chain+0x4d/0x70
    [<ffffffff8108a3b8>] __blocking_notifier_call_chain+0x58/0x80
    [<ffffffff8108a3f6>] blocking_notifier_call_chain+0x16/0x20
    [<ffffffff8125dabb>] fb_notifier_call_chain+0x1b/0x20
    [<ffffffff8125e6ac>] unregister_framebuffer+0x7c/0x130
    [<ffffffff8125e8b3>] remove_conflicting_framebuffers+0x153/0x180
    [<ffffffff8125eef3>] register_framebuffer+0x93/0x2c0
    [<ffffffffa0331112>] drm_fb_helper_single_fb_probe+0x252/0x2f0 [drm_kms_helper]
    [<ffffffffa03314a3>] drm_fb_helper_initial_config+0x2f3/0x6d0 [drm_kms_helper]
    [<ffffffffa03318dd>] ? drm_fb_helper_single_add_all_connectors+0x5d/0x1c0 [drm_kms_helper]
    [<ffffffffa037b588>] intel_fbdev_init+0xa8/0x160 [i915]
    [<ffffffffa0343d74>] i915_driver_load+0x854/0x12b0 [i915]
    [<ffffffffa02f0e7e>] drm_get_pci_dev+0x19e/0x360 [drm]
    [<ffffffff8141821d>] ? sub_preempt_count+0x9d/0xd0
    [<ffffffffa0386f91>] i915_pci_probe+0x15/0x17 [i915]
    [<ffffffff8124481f>] local_pci_probe+0x5f/0xd0
    [<ffffffff81244f89>] pci_device_probe+0x119/0x120
    [<ffffffff812eccaa>] ? driver_sysfs_add+0x7a/0xb0
    [<ffffffff812ed003>] driver_probe_device+0xa3/0x290
    [<ffffffff812ed1f0>] ? __driver_attach+0x0/0xb0
    [<ffffffff812ed29b>] __driver_attach+0xab/0xb0
    [<ffffffff812ed1f0>] ? __driver_attach+0x0/0xb0
    [<ffffffff812ebd3e>] bus_for_each_dev+0x5e/0x90
    [<ffffffff812ecc2e>] driver_attach+0x1e/0x20
    [<ffffffff812ec6f2>] bus_add_driver+0xe2/0x320
    [<ffffffffa03aa000>] ? i915_init+0x0/0x96 [i915]
    [<ffffffff812ed536>] driver_register+0x76/0x140
    [<ffffffffa03aa000>] ? i915_init+0x0/0x96 [i915]
    [<ffffffff81245216>] __pci_register_driver+0x56/0xd0
    [<ffffffffa02f1264>] drm_pci_init+0xe4/0xf0 [drm]
    [<ffffffffa03aa000>] ? i915_init+0x0/0x96 [i915]
    [<ffffffffa02e84a8>] drm_init+0x58/0x70 [drm]
    [<ffffffffa03aa094>] i915_init+0x94/0x96 [i915]
    [<ffffffff81002194>] do_one_initcall+0x44/0x190
    [<ffffffff810a066b>] sys_init_module+0xcb/0x210
    [<ffffffff8100c012>] system_call_fastpath+0x16/0x1b

    fb-test2 which reproduces above is available on bug #26232.
    To solve this issue, avoid calling lock_fb_info inside fb_set_suspend,
    and move it out to where needed (callers of fb_set_suspend must call
    lock_fb_info before if needed). So far, the only place which needs to
    call lock_fb_info is store_fbstate, all other places which calls
    fb_set_suspend are suspend/resume hooks that should not need the lock as
    they should be run only when processes are already frozen in

    Signed-off-by: Herton Ronaldo Krzesinski <>
    Signed-off-by: Florian Tobias Schandinat <>
    Signed-off-by: Greg Kroah-Hartman <>

    drivers/video/fbmem.c | 3 ---
    drivers/video/fbsysfs.c | 3 +++
    2 files changed, 3 insertions(+), 3 deletions(-)

    --- a/drivers/video/fbmem.c
    +++ b/drivers/video/fbmem.c
    @@ -1738,8 +1738,6 @@ void fb_set_suspend(struct fb_info *info
    struct fb_event event;

    - if (!lock_fb_info(info))
    - return; = info;
    if (state) {
    fb_notifier_call_chain(FB_EVENT_SUSPEND, &event);
    @@ -1748,7 +1746,6 @@ void fb_set_suspend(struct fb_info *info
    info->state = FBINFO_STATE_RUNNING;
    fb_notifier_call_chain(FB_EVENT_RESUME, &event);
    - unlock_fb_info(info);

    --- a/drivers/video/fbsysfs.c
    +++ b/drivers/video/fbsysfs.c
    @@ -399,9 +399,12 @@ static ssize_t store_fbstate(struct devi

    state = simple_strtoul(buf, &last, 0);

    + if (!lock_fb_info(fb_info))
    + return -ENODEV;
    fb_set_suspend(fb_info, (int)state);
    + unlock_fb_info(fb_info);

    return count;

     \ /
      Last update: 2011-11-10 05:19    [W:0.028 / U:6.240 seconds]
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