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Subject[2.6.30]fbdev: possible circular locking dependency in fb_mmap
Hi,

I get this warning in vanilla 2.6.30. Reverting the patch below removes
the warning.

Regards,
Jarek P.

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.30f #39
-------------------------------------------------------
Xorg/2446 is trying to acquire lock:
(&fb_info->lock){+.+.+.}, at: [<c02181c7>] fb_mmap+0x97/0x170

but task is already holding lock:
(&mm->mmap_sem){++++++}, at: [<c0106ede>] sys_mmap2+0x8e/0xc0

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&mm->mmap_sem){++++++}:
[<c0148606>] __lock_acquire+0xf26/0x17a0
[<c0148ede>] lock_acquire+0x5e/0x80
[<c016f72b>] might_fault+0x8b/0xb0
[<c01f8a36>] copy_to_user+0x36/0x120
[<c0194f54>] filldir64+0xa4/0xf0
[<c01cbbc9>] sysfs_readdir+0x129/0x220
[<c01951e6>] vfs_readdir+0x86/0xa0
[<c0195269>] sys_getdents64+0x69/0xc0
[<c0102f49>] syscall_call+0x7/0xb
[<ffffffff>] 0xffffffff

-> #2 (sysfs_mutex){+.+.+.}:
[<c0148606>] __lock_acquire+0xf26/0x17a0
[<c0148ede>] lock_acquire+0x5e/0x80
[<c0303877>] mutex_lock_nested+0x57/0x300
[<c01cbfcc>] sysfs_addrm_start+0x2c/0xb0
[<c01cc580>] create_dir+0x40/0x90
[<c01cc5fb>] sysfs_create_dir+0x2b/0x50
[<c01f1ff2>] kobject_add_internal+0xc2/0x1b0
[<c01f21e1>] kobject_add_varg+0x31/0x50
[<c01f225c>] kobject_add+0x2c/0x60
[<c02699ba>] device_add+0xca/0x560
[<c0269e62>] device_register+0x12/0x20
[<c0269f12>] device_create_vargs+0xa2/0xb0
[<c0269f48>] device_create+0x28/0x30
[<c026448d>] register_con_driver+0x14d/0x190
[<c02678db>] take_over_console+0x1b/0x430
[<c0221fbc>] fbcon_takeover+0x5c/0xb0
[<c0225f3e>] fbcon_event_notify+0x7de/0x810
[<c013bfad>] notifier_call_chain+0x2d/0x70
[<c013c344>] __blocking_notifier_call_chain+0x44/0x60
[<c013c37a>] blocking_notifier_call_chain+0x1a/0x20
[<c0217ac1>] fb_notifier_call_chain+0x11/0x20
[<c0218b23>] register_framebuffer+0x173/0x230
[<c041edc2>] vesafb_probe+0x542/0x783
[<c026cbbc>] platform_drv_probe+0xc/0x10
[<c026bcf4>] driver_probe_device+0x74/0x190
[<c026bef1>] __device_attach+0x41/0x50
[<c026b35b>] bus_for_each_drv+0x5b/0x80
[<c026bf9b>] device_attach+0x6b/0x70
[<c026b167>] bus_attach_device+0x47/0x70
[<c0269c20>] device_add+0x330/0x560
[<c026d58d>] platform_device_add+0x15d/0x1a0
[<c041f09d>] vesafb_init+0x9a/0x1ec
[<c010111a>] do_one_initcall+0x2a/0x160
[<c04044f5>] kernel_init+0x8d/0xe1
[<c010372b>] kernel_thread_helper+0x7/0x1c
[<ffffffff>] 0xffffffff

-> #1 ((fb_notifier_list).rwsem){.+.+.+}:
[<c0148606>] __lock_acquire+0xf26/0x17a0
[<c0148ede>] lock_acquire+0x5e/0x80
[<c0304231>] down_read+0x41/0x60
[<c013c32a>] __blocking_notifier_call_chain+0x2a/0x60
[<c013c37a>] blocking_notifier_call_chain+0x1a/0x20
[<c0217ac1>] fb_notifier_call_chain+0x11/0x20
[<c0218b23>] register_framebuffer+0x173/0x230
[<c041edc2>] vesafb_probe+0x542/0x783
[<c026cbbc>] platform_drv_probe+0xc/0x10
[<c026bcf4>] driver_probe_device+0x74/0x190
[<c026bef1>] __device_attach+0x41/0x50
[<c026b35b>] bus_for_each_drv+0x5b/0x80
[<c026bf9b>] device_attach+0x6b/0x70
[<c026b167>] bus_attach_device+0x47/0x70
[<c0269c20>] device_add+0x330/0x560
[<c026d58d>] platform_device_add+0x15d/0x1a0
[<c041f09d>] vesafb_init+0x9a/0x1ec
[<c010111a>] do_one_initcall+0x2a/0x160
[<c04044f5>] kernel_init+0x8d/0xe1
[<c010372b>] kernel_thread_helper+0x7/0x1c
[<ffffffff>] 0xffffffff

-> #0 (&fb_info->lock){+.+.+.}:
[<c0148945>] __lock_acquire+0x1265/0x17a0
[<c0148ede>] lock_acquire+0x5e/0x80
[<c0303877>] mutex_lock_nested+0x57/0x300
[<c02181c7>] fb_mmap+0x97/0x170
[<c01768d6>] mmap_region+0x2d6/0x450
[<c0176c1a>] do_mmap_pgoff+0x1ca/0x2f0
[<c0106efd>] sys_mmap2+0xad/0xc0
[<c0102ec8>] sysenter_do_call+0x12/0x36
[<ffffffff>] 0xffffffff

other info that might help us debug this:

1 lock held by Xorg/2446:
#0: (&mm->mmap_sem){++++++}, at: [<c0106ede>] sys_mmap2+0x8e/0xc0

stack backtrace:
Pid: 2446, comm: Xorg Not tainted 2.6.30f #39
Call Trace:
[<c0302400>] ? printk+0x18/0x20
[<c01471e3>] print_circular_bug_tail+0xc3/0xd0
[<c0146f0b>] ? print_circular_bug_entry+0x4b/0x50
[<c0148945>] __lock_acquire+0x1265/0x17a0
[<c015e0ab>] ? __generic_file_aio_write_nolock+0x23b/0x590
[<c014699c>] ? trace_hardirqs_on_caller+0x11c/0x160
[<c0148ede>] lock_acquire+0x5e/0x80
[<c02181c7>] ? fb_mmap+0x97/0x170
[<c02181c7>] ? fb_mmap+0x97/0x170
[<c0303877>] mutex_lock_nested+0x57/0x300
[<c02181c7>] ? fb_mmap+0x97/0x170
[<c01832d5>] ? kmem_cache_alloc+0xb5/0x100
[<c014699c>] ? trace_hardirqs_on_caller+0x11c/0x160
[<c02181c7>] fb_mmap+0x97/0x170
[<c01768d6>] mmap_region+0x2d6/0x450
[<c0176c1a>] do_mmap_pgoff+0x1ca/0x2f0
[<c0106efd>] sys_mmap2+0xad/0xc0
[<c0102ec8>] sysenter_do_call+0x12/0x36

------------------>

commit 513adb58685615b0b1d47a3f0d40f5352beff189
Author: Andrea Righi <righi.andrea@gmail.com>
Date: Mon Apr 13 14:39:39 2009 -0700

fbdev: fix info->lock deadlock in fbcon_event_notify()

fb_notifier_call_chain() is called with info->lock held, i.e. in
do_fb_ioctl() => FBIOPUT_VSCREENINFO => fb_set_var() and the some
notifier callbacks, like fbcon_event_notify(), try to re-acquire
info->lock again.

Remove the lock/unlock_fb_info() in all the framebuffer notifier
callbacks' and be sure to always call fb_notifier_call_chain() with
info->lock held.



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